FOLLOW UP: I'd like to use this pinned comment to expand on some of the details that I glossed over/missed in the video. A lot of these details are contributed by thoughtful commenters, which I really appreciate! 1. Please keep in mind that the video is talking about the reciprocating group as one mass and ignoring the interaction between the different components. I wanted this video to be applicable to gas operated firearms as a whole. Here are some of my thoughts about the quirks of the AR platform if you're interested: The buffer doesn't contribute kinetic energy for unlocking, bolt pickup, and overcoming any friction/forces that resist solely the bolt carrier during the rearward stroke (e.g: hammer spring force). However, it does help everything in the forward stroke. A few commenters mentioned lightening the bolt carrier but increasing the buffer weight as a method to soften the felt recoil. This works because even though the overall reciprocating mass is the same, a larger portion of that mass is now in the form of the movable buffer weights, which spreads out the impulse of the reciprocating mass over a larger amount of time. The flip side is that the lightened bolt carrier now has lower kinetic energy to overcome the previously mentioned resistances during the rearward stroke. 2. Is it reasonable to assume that both reciprocating masses takes the same amount of time to come to a stop after bottoming out (5:23)? This amount of time is dependent on a few things like the stiffness of the buffer material, the butt pad, and how stiff the shooter is holding the gun. Additionally, the impulse transferred to the gun when the reciprocating mass bottoms out is also dependent on the rebound velocity after it bounce off the rear of the receiver (after removing the contribution of the recoil spring). I could not find a way to account for all of that, so I made an over-simplistic, catch-all assumption that the impulse time is the same, and did not include the time after v=0 into the impulse time. This is for the sake of being able to compare the impact force, which I think is more intuitive to understand. The more accurate thing to do would be to just stop at comparing the impulses of of the reciprocating mass striking the receiver, where the impulse could be understood as the capacity to apply a force over a length of time. 3. Another over-simplistic assumption that I made is that the gas system provides the same amount of kinetic energy to the reciprocating group regardless of mass (1:45). The amount of KE provided by the gas system is the mechanical work done by the propellant gas on the reciprocating mass. This can be calculated by taking the integral of the force applied to the working surface of the gas piston over the distance of travel during which the piston is pressurized. (Note: in the AR-15, the "working surface of the gas piston" is the rear surface of the gas chamber inside the bolt carrier). In the video, I compared a gun with standard gas and standard mass to a gun with standard gas and low mass, so I assumed that the gas system has enough pressure to apply roughly the same force during the entire pressurized stroke of the piston. However, if you use an overly heavy reciprocating mass for a given gas system, an interesting thing starts to happen. The pressure inside the gas chamber drops over time as the bullet goes pass the gas port and exits the muzzle. An overly heavy reciprocating mass will accelerate very slowly, which means the gas pressure can drop significantly during the pressurized stroke. Therefore the force-distance curve of the piston will drop, the area under the curve will drop, meaning the kinetic energy provided to the reciprocating mass by the gas system will reduce. TL,DR: In real life, if the reciprocating mass is too heavy for a given gas system, you can reduce the amount of kinetic energy provided by said gas system, and the gun might short stroke. 4. Another obvious, but implicit assumption I made in the video is that in both guns, the reciprocating mass bottoms out on the back of the receiver. This is true for most military weapons. If you tune the gun so that the reciprocating group does not bottom out, then it categorically changes the recoil behaviour, and the math I used no longer applies. What would still apply is that an overly lightweight reciprocating group would still decelerate faster, and you would still have a harder time balancing a slow enough initial velocity for extraction, and fast enough to complete the cycle. If you want to know more about cases where the reciprocating group does not bottom out, then patent US4475438A is a good read. It's Jim Sullivan's patent on the constant recoil system. And it's more complicated than just making the reciprocating mass not bottom out. 5. A viewer brought up an interesting detail about the AR platform. During the extraction phase, after the bolt has unlocked, the extractor momentarily lifts off the rim of the fired casing. It is the residual chamber pressure after unlocking that presses the case into the bolt face, allowing the extractor to fall back down and grab the case rim again for ejection. A few tests showing this phenomenon were detailed in a May 2003 US Army TACOM presentation, titled "Understanding Extractor Lift in the M16 Family of Weapons". Supposedly, the implication of this is that the initial BCG velocity is important because if it's too fast, the BCG recedes faster than the residual chamber pressure can press the case into the bolt face, leading to failures to extract.
US ordnance (the government) found that, to have a reliable selfloading firearm, you need a Bolt carrier:Bolt mass ratio of about 3:1 or greater. the greater, theoretically the more reliable. SCAR17 is at 8.8:1. M1 is at 1.75, M14 is at 1.45. This is very low, but the M14 doesn't lose much relative to the M1 for that loss. It's more that they would gain a lot of energy retention from getting to 3. AR15 has 4.68 for a full auto normal Colt BCG. K1 has 5.88 AKM is at 5.4
Thank you for an outstanding video and follow-up clarifications! While I agree there is more to Constant Recoil than simply keeping the bolt from bottoming out, that is a huge benefit unto itself. Many commenters on videos about Constant Recoil claim that it would be useless or have no effect in semiautomatics. That's like saying that switching out your dirtbike's long-travel springs for scooter suspension would be equally controllable or comfortable on a rocky trail. The effects of inadequate free recoil travel are readily apparent in subcompact pistols. Not only is recoil worse, but the springs are much stiffer (offer more resistance during the critical ejection portion of the recoil stroke) to avoid it being MUCH worse.
"Is it reasonable to assume that both reciprocating masses takes the same amount of time to come to a stop after bottoming out". No, a more reasonable assumption is that the effective spring constant will be the same, which means the heavier mass will apply force for longer (but still more force). As you say though, just compare impulses. More importantly though, the BCG slamming into both ends isn't the only impulse -- there's also the impulse directly transmitted to the receiver through the locking lugs. Pump action shotguns don't have *any* recoiling mass when fired, while semi-autos do and this makes them softer shooting. This is because the direct impulse is lessened, and then spread out over time with the recoil spring. "Another over-simplistic assumption that I made is that the gas system provides the same amount of kinetic energy to the reciprocating group regardless of mass". This is another incorrect assumption. It's more of a fixed impulse, and heavier BCG will have less energy for that same imparted momentum. This is why decreasing the mass makes it overgassed unless you turn the gas down to compensate. Other than that though, I think it all checks out
A viewer recommended a channel called "Konstantin Konev" to me. Dude's an actual firearms engineer, worked for LMT. His channel is an absolute treasure trove of firearms knowledge. The only thing is that it's all in Russian lol
@@ipanzerschrecku4732to be fair full auto isn't even really used in the military unless you are just burning ammo after a range. Soldiers are taught to prioritize accurate semi auto fire to increase accuracy and conserve ammo.
@@nemisous83 Frankly it sounds to me that you have absolutely no idea what mode of fire "a military" uses or have any clue what you're talking about. You're just regurgitating something you've heard somewhere taking it completely out of context and you're just the guy that chimes in with something stupid without making much sense.
@@nemisous83also full auto fire power is very effective in gaining fire superiority and suppressing the enemy hense why a modern day infantry squad is built around a GPMG where the individual rifleman can substitute fire and movement. You literally have no clue but you felt the need to chime in with a know it better attitude built on pure ignorance regurgitating something you've heard somewhere about a very specific scenario for a tiny tiny little group in the military of special forces soldiers and even then it's garbage because those very same groups use extreme amount of firepower to get out of trouble if need be using massive amounts of full auto fire if ambushed for example.
Years ago, I was really, REALLY into high performance paintball guns. One thing that we learned was that low reciprocating mass was preferred, but as the mass lowered the cycle speed would almost invariably increase. Adjustable gas regulators could tune in the gas pressure and a solenoid valve would handle volume. With these two parameters, we could better control bolt dwell time. Often though, thr smoothest shooting guns had the lightest bolts, and the LOWEST FRICTION design. Friction was the hardest thing to overcome when trying to achieve a smooth shot cycle. Something to think about in your next AR build.
It'd be interesting if we start seeing "low friction" BCGs and uppers with less/smoother contact surfaces to reduce felt recoil.... or are these already a thing for competition?
@@calebnation6155 same here, grease for the sliding parts and oil for the rotating parts. Most people don't grease their cam pins but I think it's very important to prevent wear in the cam pin channel as well as to help dampen the forces on the cam pin during cycling.
I believe the gun should fit the time-place-occasion, if it's supposed to work in many different conditions, eliminating variables with a heavier BC is a good idea, but if its a competiton gun that doesn't fire full auto and only semi, i think there is a decent trade off to be had with a lighter BC
For non-match guns, I like to run the heaviest buffer I can get away with for just that reason. Also keep in mind the heavier, mil spec carriers will lost a lot longer than lightweight units.
I think one difference is that the amount of kinetic energy added from the acceleration off the gas piston would be less for the lighter one. The length of the gas piston is fixed, and would spend less time accelerating on it due to accelerating faster and traveling that fixed distance sooner.
Great video. One point to contextualize Sullivan's comments in Ian's interview that he would rather increase the mass: his point of view centers around full-auto firing. As you point out, there is an impulse when the reciprocating components bottom out (often referred to as secondary recoil) as well as an impulse when the reciprocating components go into battery (tertiary recoil). Primary recoil of course is caused by the bullet being accelerated downrange. From the perspective of the shooter when firing full auto, tertiary recoil from the preceding round occurs contemporaneously with primary recoil from the successive round. As these impulses are in opposite directions, they can nearly cancel out in a well-tuned system if that is one of your design goals, as it is in some of Sullivan's designs that came after the AR15. Reducing the mass of the reciprocating components drops the momentum they have when entering battery as you point out, and thus reduces the tertiary recoil impulse that would cancel out the next primary recoil impulse. This is why Sullivan thinks it's crazy to reduce the mass: it's counter to his design goal of "constant recoil" under full-auto fire. Of course, if you have primary and tertiary recoil working in harmony you haven't necessarily done anything about secondary recoil. Sullivan's modification to the AR15 design also incorporates a carrier designed for a longer stroke, with more wiggle room in the travel distance between bottoming out and being able to strip a round from the magazine. This allows his system to be tuned to never bottom out or at least not do so heavily, where the reciprocating components are halted in their rearward motion primarily via friction and spring pressure over a longer duration. In this situation, the push the shooter feels is simply the pressure the reciprocating components apply via the spring and friction, which does oscillate but with a much smaller delta than a system where the moving parts come to a sudden stop. With secondary recoil minimized, the weight of the reciprocating components is no longer an issue there and they can be made heavier to help the tertiary recoil cancel out primary recoil in full-auto, which is exactly what Sullivan has done. The system can now be said to be in a state of "constant recoil" for marketing purposes. Sullivan's AR15 design modification for "constant recoil" was commercialized in the form of the Surefire OBC.
Thank you for pointing out the importance of the ratio of bolt weight to reciprocating mass (bolt carrier + buffer). Early in the development of the AR-10 the bolt carrier and buffer were a single part. A reduced weight buffer would be a lot cheaper than a reduced weight bolt carrier.
Bro I had been doing so much digging on the internet for stuff like this! To theorize a perfectly tuned “felt-recoil free” service rifle, I even resorted to retaking online physics lessons. Thank you so much for putting out this video!
Please make more content like this I thought I would be bored but I came out smarter and more informed on not just the pros and cons of weights of BCGS but a little bit of trivia on another weapon system
Great video. It would be nice to see a video with calculations for a "properly optimized" system used for 3G guns. Should be very helpful to understand how much "round stripping" and "bolt bounce" are affected and if it is really an issue. Anecdotally, the following values work flawlessly on many guns, various calibers/loads and environmentals: 1. GAS port restriction: 40% (estimation) 2. BCG weight reduction: 30% (-4Oz) 3. Buffer weight reduction (reciprocating part only): 80% (-2.4Oz) 4. Recoil spring strength reduction: 10%
Good video. I think you pretty much covered all angles of this issue. It's all about maintaining adequate spring work and momentum on feed within the range of mechanically optimal velocity and magazine safety time.
Sick video. Awesome job. Please post more content like this. Maybe something on spring forces and how they interact would be great or about gas pressure, etc.
If you look at the A5 system, it is designed to allow for more weight and a higher sprung carrier as it gives the carrier more "oomph" to trudge through any debri and get you solid bolt closing. Makes sense. Not to mention, you can run into bolt bounce issues with improper tuning.
The largest advantage of the A5 system and its copies isn't its ability to have more buffer mass, it's the biasing of the buffer weights and the use of a longer recoil spring for the same stroke (no, despite what you learned in high school Hooke's law is not a complete descriptor of spring behavior)
Fantastic video. I think this is very helpful for explaining the “tuning” process of an AR, by altering Gas, Mass, and Spring. I think more videos diving into the other variables to find ways to either minimize recoil, maximize reliability, or increase the operating envelope, would be very valuable.
Great video and it helps explain why I ordered that lightweight BCG for my subsonic 300BLK build since the F is inherently lower to begin with so I don't get the negative effects of lower m. [Update: And it works!]
If you add a stronger recoil spring to counter the increased velocity, then adjust the gas for reliability, you can increase reliability over the lighter bolt carrier by itself. You are essentially trading bolt mass for bolt velocity to maintain reliability.
This content is amazing. You definitely earned my subscription. Out of curiosity, would having a stronger spring plus more gas coming from the gas block help solve this issue? I don't know too much about guns so there might be some problems with what I'm thinking.
Part of this is the ratio of weight of the carrier to bolt , IF you look at one of the design changes made to the AKM to AK74 , you will see a lighter weight AK74 bolt ( the stem is reduced diameter ) , this gives the AK74 higher carrier to bolt weight ratio , to give the bolt more force in chambering/locking , my the higher mass ratio .
Great examples of this Bravo. I run a 2A Armament titanium bolt carrier that has a gas adjustable feature on the bolt carrier itself. I run it with a Geissele super 42 buffer spring and an H3 buffer. Once I dialed the gas in its absolutely flawless and insane smooth. Just my 2 cents worth.
A milspec BCG is about 11.6 oz and a standard CAR buffer is about 3.0 oz for a total 14.6 oz or so. I did similar with my WWSD build, getting a Faxon Gunner lighweight BCG (8.5 oz) and H2 buffer (4.6 oz) for about 13.1 oz total recip mass, shifting the COG a little rearward. Reliability has been great, seems like less friction from having less surface area.
love everything your saying and i also have seen all the interviews/videos and such my irl gun is a m16a1 with muzzle break and 9oz bcg and its 100% recoiless i actually want to design my own bcg that is ultra light
Great vid. A not insignificant difference with changing reciprocating mass is time in battery. Obviously most of us can’t calculate the difference but it can be quantified through performance and it should be considered.
As someone who has built two AR's with titanium BCG and lightweight buffers, an adjustable gas block is 100% needed. My picks are either the Riflespeed or Superlative Arms. I haven't used the Riflespeed but it seems very easy to adjust, although it seems to have less adjustment and no bleed-off like the ones from superlative arms. Reliability is really only an issue if I run lower pressure .223 rounds, but with that said 1-3 clicks to open the gas block fixes that. Also these AR's are ran suppressed, the Superlative Arms bleed off really shines here as most excess gas is bleed off at the gas block and not at the BCG, so less gas in your face.
Fair assertions. To simplify the math all down to one sentence: Newton's laws of motion tell us all we need to know (particularly the 2nd and 3rd laws). Speaking on the lightened bolt carrier subject, I have a WWSD2020 I personally tweaked to be as light to carry, and as light recoiling as possible - within acceptable parameters. It comes with JP's silent captured spring, which has adjustable springs - I put the heaviest one in there. I changed the bolt carrier out for a low mass BCG from Brownells. I put on a Superlative adj. gas block with the correct gas journal. Then I tweaked the gas a handful of clicks above cycling flawlessly with low power .223 ammo. What I sacrificed in reliability, I gained in performance and weight savings. As a civilian, that's an acceptable trade.
Привет, классное видео , кое что новое я услышал про вес затворных рам ,могу отметить что решение с газ регулятором достаточно сомнительное , есть смысл ставить газовый поршень (кучность слегка упадёт) . Hello, cool video, I heard something new about the weight of bolt carriers, I can note that the solution with a gas regulator is quite dubious, it makes sense to install a gas piston (the accuracy will drop slightly).👍👍
When I ran lighter BCGs in my carbine style AR10s, I knew it would increase the velocity of the BCG, which in turn would cause additional wear on the hammer, buffer spring, buffer and eventually the BCG itself. So when using one, I've always used them in conjunction with a slightly stronger buffer spring and a hydraulic oil piston buffer to nullify the negative effects.
Great video! I'm curious to see what you think of the Foxtrot Mike FM-15 bufferless uppers. These also use a modified shortened carrier, but from what I've heard are far more reliable than the ARIC Bufferless BCG.
Good video. Though, I’ve got to rein in my expectations on “nerdy”. I was expecting stress analysis and fatigue life on different bolt carrier groups comparing different materials.
Great nerd talk. Another thing to add, militaries also have full auto. Which makes bolt carrier bounce and high cyclic rates a bigger issue and also favors heaver setups. And the DT Wolverine, so basically MDR generation 3, seems to have some magazine locking issues. Time to wait for the gen 3.1 hot fix in a month or two from now.
The "problem"/best point of this video is the "fair" comparison. For high level competitive shooters, they do not just make a single change, like a lighter BCG; that is just one of MANY major upgrades they make. This is a problem, as it doesn't reflect the complex nature of the total modifications made; however, it is the best point in that thinking you can just change out a lighter BCG and your gun is going to be just as reliable is not realistic. To expand on that, high level shooters also do TONS of testing and tweaking parameters to tune their equipment precisely; they don't just buy upgrade parts and slap them in, as most people think they can. Ammo is a VERY important factor; competitive shooters require much more precise ammo than most people, and are tuning the rifle to generally just 1 load, which is the only load they shoot out of the gun ever. Factory guns are designed to work with any ammo that falls within SAAMI specs, instead of only one load. Reduced recoil spring pressure is great, so long as you clean the gun after every match, keep it clean during the match, and if it's dusty out then you open it up and wipe it out between stages! Competition race guns are amazing and blazing fast; however, they require much more maintenance, are not quick or easy to set up and tune, and are not reliable with a wide variety of factory ammo.
Great vid! BCG mass and carrier to bolt head mass ratio are often regarded as some of the more important factors when it comes to reliability. I have a few questions on the topic of recoil tho, given a certain BCG mass. Over the years of watching gun videos on youtube I have heard comments saying that "snappy" recoil is better for semi, and constant recoil doesn't do much for semi. On the other hand, I've heard ppl say the 556 MDR and the RDB have low recoil due to their longer than usual (but not quite constant recoil level) recoild stroke. Which one in your opinion is true?
I think it's mostly coming down to personal preference. It goes back to the impulse equation at 4:55. Assuming the initial BCG momentum is the same, if you have a slower recoil cycle like the MDR and RDB, the time increases and the force reduces. Opposite is true for a faster recoil cycle. When I shot low powered .223 in my X95, the BCG velocity is slower, and it feels like a gentle push. If I switch to hotter 5.56 then it's a quicker but harsher snap. I can see the pros and cons of both cases. A gentler push doesn't knock my sights off target as much, but the recoil cycle is slower and my sights are off target for longer. A quick snaps knocks my sights off a bit more but it also goes back on target faster.
I'm gonna say it depends a bit. I've had more trouble tracking sights with some snappy recoil, but "pushy" for lack of a better term, you can keep a better sight picture and just push it back on target. I'd say it all comes down to how much total recoil you're going to see, whether getting it over with fast vs spreading it out is going to be a better strategy. In 5.56? Quick snap is probably going to be better, because total recoil is really low. .308? Might want to spread that recoil out a bit. A snappy 12 gauge? No thanks. I have a 3" barrel .44 Mag. It's the extreme of "snappy" recoil. The gun is just suddenly in a different place. It'd be a lot more controllable as a longer push.
The amount of velocity/energy that the rebound of the reciprocating mass gives to the return to battery stroke is non-trivial. It's based purely on velocity; faster cyclic rate (rearward velocity during spring compression) increases the amount of energy returned via the rebound off of the far end of the receiver extension. Also, just run an FA carrier and use the Vltor A5 system. 👍
I did make my math a bit oversimplistic when I only looked at the length of time between the bcg bottoming out and coming to a point of zero velocity. I didn't know the equation for rebound velocity (or if there is an equation), so I just swept that under the rug for the sake of having a clean impulse equation with the same end point lol
@@cabbage6015 I think you did a superb job and would love to see you dive even deeper in future videos. I would have made the same decision you did. Keep it up!! 👍☺️
Ive owned every MDR generation and am very familiar with its changes and drawbacks. Youre right about the light carrier problem, but another issue that plays into this whole tuning dynamic with gas operated rifles is the location of the gas port and the geometry of the bolt carrier cam path. Desert Tech chose to rectify the rim ripping issue, present only in the 308 rifles, by increasing the size of the extractor along with modifying the gas plug. Moving the gas system further from the chamber, or by lengthening the cam path helps reduce the ammount of energy needed to cycle the weapon as well by allowing chamber pressures to drop to lower levels at the time of extraction. Imo changing the reciprocating mass should be one of the last variables you address when tuning a rifle, whether that be for duty or competition.
Subscribed, because we need more of this. I think more reciprocating mass should be moveable buffer as opposed to solid. Per my understanding/guess, the moveable buffer mass essentially does the positive things that solid mass does, but requiring less mass. Maybe the initial part is a little worse - the unlock has less mass, of course, but you should get a little delay/slowing at the end of the travel due to the moveable mass, and then of course, it should also help the forward motion back into battery. I’ve wanted to test a heavy buffer and lightweight carrier for a long time, ideally ending up a few oz lighter than a standard system, but haven’t had time. What are your thoughts? Why am I wrong?
I think it's a good idea generally. Moveable buffer weights spread out the impulse of the reciprocating group striking the rear of the receiver extension, because instead of one large mass impacting at once, it's multiple smaller masses impacting throughout a larger length of time. It works to kill bolt carrier bounce too, but I guess that's not too important in semi auto. If the total mass is the same as a solid reciprocating group, it will store the same kinetic energy to overcome springs and frictions, so yes it retains most of the benefits of the same solid mass. There's just one quirk which is the buffer mass does not help the unlock and pickup of the bolt, only the carrier mass does, but unless one doesn't go overboard in reducing carrier mass it should be fine. The only thing I might not agree with you is when you said moveable buffer mass does the positive things that solid mass does, but requiring less mass? I could be wrong tho
@@cabbage6015thank you - I meant *some* of the positives, such as improved delay at end of travel, allowing for the magazine spring to push up the next round, and then acting like a dead blow when feeding that round. Obviously they (free or semi free moving mass, and solid mass) behave differently. The only thing I worry about is the initial unlock and velocity rearward, although that should be able to be addressed with adjusting the gas system. Thanks for your input, hope you end up having more thoughts on the subject at some point. A video on hydraulic buffers would be incredibly interesting. Cheers
The recipe for a reliable ar-15 with low mass BCG is to install adjustable gas block while retaining the stock buffer spring. You tune the gas block so it ejects the brass perpendicularly from ejection port and the spring rides the bolt back in with enough energy to close the bolt.
Would you ever be interested in making a video about how muzzle brakes and compensators affect shotguns differently than rifles/pistols/etc.? The physics behind it are neat if you want something to dive into.
I wanted the lightest rifle possible and achieved a weight of 4.2 lbs without carbon fiber. The bolt carrier is skeletonized steel (Faxon), the buffer is a hollow plastic piece that weighs about a gram, and the recoil spring is reduced 10%. All of this necessitated an adjustable gas block of course, and it is set at 50%. The rifle also has an integrated muzzle brake. There's almost no recoil if you're shooting White Box, but the Tula steel cased stuff does introduce a bit of it as it is hotter. Despite minimal gas, the extractor does try to rip the rims off the cases it seems, although the damage to the cases is minimal. The reciprocating mass is just too light and the BCG needs the velocity to fully cycle. Another issue I suspect is occurring is bouncing at lockup. The reduced mass and spring weight may allow the BCG to bounce back slightly when going into battery, although I've had no malfunctions with this setup (except when I used way too much oil). I could fix both the bouncing and rim-grabbing issues by filling the hollow plastic buffer halfway with lead shot. This would give a deadblow hammer effect at both ends of movement and add a little mass back into the system.
It's important to point out that the LAW ARIC showed in the gun used by MAC was correctly installed, you can tell because the guide rods are too far forward when installed in the gun, they should be further to the rear of the cutout. This means the cup was not properly seated which will greatly increase the friction when it trys to cycle, leading to the issues seen in his video.
The amount of ke absorbed by the spring isn't the same, because the time it has to act is different. I would recommend looking at it in terms of momentum anyway. At any given amount of compression there will be a certain force but the amount of time spent at any given force is longer for the high mass variant. This can be derived intuitively by remembering that if the mass is too heavy in your AR, it will short stroke and never bottom out. Therefore, a mass that never reaches the end cannot have the same ke at the end point as a mass that does. Mathematically when you bring out the impulse formula you're very close to being correct, you just should have applied it to the earlier part of the video. ∆p=∫f∆t and so an integral with the same force curve but stretched over a longer t will be a much larger area under the curve. On the forward stroke you're correct though because the spring will be able to increase the p of the bcg more so a lightweight bcg will have less forward recoil, but more rearward recoil. The rest of the video is spot on. Overall I like the video a lot. I don't mean to be too hard on you, it's a good video and I'm definitely subscribing.
I really appreciate your comment, but I'd have to respectfully disagree. The elastic potential energy stored by a spring is given by E = (1/2)k(∆x)^2. It only depends on the change in length and spring constant, not time. No matter how long the mass is staying at a certain point of spring compression, the energy absorbed is the same. What you mentioned about ∆p=∫f∆t relates to the impulse transferred from the spring to the bcg as it retracts, and yes that impulse does increase if the time is stretched out longer, but that's impulse and not kinetic energy. The reason my calculation did not account for the case where an overly heavy bcg would short stroke is because of another assumption that I've made, which is the gas system provides the same amount of kinetic energy to both guns (1:45). Irl, the energy provided by the gas system can be calculated with the mechanical work formula, which in this case would be an integral over distance of the force applied to the rear wall of the internal gas chamber inside the AR-15 bcg (or force applied to the front surface of the gas piston on external piston guns). That force is dependent on the gas pressure, which drops over time as the bullet goes past the gas port and exits the muzzle. If the bcg is overly heavy, it would accelerate slower (F = ma), and thus the force over distance graph would drop more, the area under the force-distance curve will reduce, meaning less kinetic energy is provided to the bcg. My assumption that the gas system provides the same kinetic energy in both cases does not hold up in reality if the bcg mass increases past a certain amount, and I missed that when scripting this video for sure. I've also failed to mention a few other assumptions, such as the the bcg will bottom out in both cases, which might not happen irl and will drastically alter the recoil sensation. Overall I do think myself that the math I've used is oversimplistic. And no worries, I didn't take your criticism personally. Again I really appreciate you taking the time to comment, and I really love having in-depth discussions like this about my videos after I post them. I'm glad that you mentioning the case of an overly heavy bcg pointed out a mistake in my assumption about the amount of kinetic energy initially provided. Really love what you're doing on your channel btw. I wish I can get a chance to tinker with firearm designs like that, but alas, the gubermint just banned the possession of firearms CAD files up here in Canada 😅
@@cabbage6015 Oops, I definitely got that ke part wrong, I started thinking about momentum and then wrote about ke. You’re correct that the amount of KE stored in the spring is determined by the constant and displacement alone. The thing is, recoil isn’t a function of kinetic energy; it’s a function of momentum. The momentum of a system is conserved, so the bullet and gas going in one direction (with a certain amount of momentum) will be offset by an equal and opposite amount of momentum in the opposite (rearward) direction no matter what the recoil system or weights are. What we feel as recoil is this momentum being transferred from the gun to us, but there is no way to change the total amount of momentum transferred due to conservation of momentum. Even though the total area under the curve is unchangeable, the shape of the curve is and “Felt recoil” is more so the peak impulse, which we can change. While the bolt is locked, the momentum is largely transferring to the frame of the gun alone (in a bolt action this is all that happens) but as soon as the bolt is in motion it picks up the remainder of the momentum and it’s motion rearward is slowed because the spring is transferring momentum from the bcg to the non moving reciprocating portions of the gun. A heavier bolt will be locked longer, thereby frontloading the momentum transfer, but it will also give the spring more time to exert force, and the integral of force over time is change in momentum therefore it’s bleeding off more momentum which is why a heavier bolt is less likely to bottom out. If the bolt bottoms out, it will dump the remainder of the momentum and this will typically be the peak impulse. The forward stroke also isn’t a function of KE, it’s a function of momentum where the spring acting longer is able to transfer more momentum into the bolt before it closes and causes the front of the gun to dip. So the peak impulse is less with a heavier bolt, and the curve overall should be flatter and longer, but the forward momentum and dip of the gun will be more due to increased time to close the bolt.
I agree to conservation of momentum part, which is why I worded my conclusion as the heavier reciprocating group disrupts the sight picture more as is impacts the back and front of the gun, and not that it gives the gun a higher rearward momentum after the firing cycle is completed, because that would be wrong. From what I understand from Jim Sullivan's constant recoil patent, in a gas operated gun where the reciprocating group bottoms out, there are 6 ways the rigid frame of the gun receives momentum throughout 1 complete firing cycle: (1) The rearward impulse transferred to the rigid frame through the locked bolt as the bullet goes down the barrel (2) The forward impulse transferred to the rigid frame by the gas pressure applied to the front wall of the gas chamber (3) The rearward impulse transferred to the rigid frame through the recoil spring as the reciprocating group moves back (4) The rearward impulse transferred to the rigid frame as the reciprocating group bottoms out on the back of the receiver (5) The rearward impulse transferred to the rigid frame through the recoil spring as the reciprocating group is pushed forward (6) The forward impulse transferred to the rigid frame when the reciprocating group strikes the front of the receiver And yes, all 6 of these impulses combined will give the gun a momentum opposite in direction and equal in magnitude of the bullet and gasses leaving the front of the gun, as you said. Among these impulses, Imo (4) and (6) are sharp spikes that disrupts the sight picture way after the shot is first ignited, and are influenced by the reciprocating mass, which was why I wanted to focus on them for the video. I think your derivation of the rearward momentum as the BCG bottoms out is mistaken because the your impulse (1) is smaller than the impulse of the bullet, and if I understood you correctly, what you were saying is that (1) + (3) + (4) will equal the bullet impulse. You were missing (2), (5) and (6). According to Jim Sullivan, (1) should be equal to the negative of the bullet impulse. (2) is the impulse given by the gas to the front wall of the gas cylinder, and should be equal in magnitude but opposite to the direction of the impulse given to the reciprocating mass. (Later on the momentum provided to the reciprocating mass by this process will come back to influence the rigid frame as impulses (3), (4), (5), and (6)). As you said, a heavier BCG would accelerate slower, so the time that the gas pressure applies force on both the gas chamber and the BCG should be longer, leading to a higher impulse on both parts. Basically a heavier BCG should have higher momentum at the beginning of the rearward stroke. Whether or not it will still have higher momentum when it bottoms out will depend on the time it spends under the force of the recoil & hammer spring (compared to the time a lighter BCG would spend). To eliminate time as a variable, I used energy calculations since they're independent of time. And while as you said, energy calculations cannot be used to describe what is the force applied to the rigid frame of the gun while the BCG gets from the front to the rear of the receiver and vice versa, they should be valid to get us to the end points, by allowing us to derive the velocity at the end point in terms of mass, and sub that into the momentum equation. Ultimately, that was what I did.
I think the difference on recoil is even more pronounced with handguns. Shooting a P320 full size slide along with a P320 X-Five slide with its factory lightening cuts, all on the same frame, the difference is really evident. It's a lot easier to track the sights through recoil on the X-Five. But that pistol really didn't like it when I tried adding a compensator. The regular full size just took it and ran...
Physics student here, 5:12 . Sometimes when you need to calculate the integral of a changing/dynamic force. It could be way easier to use conservation of energy formulas ( as they don't depend on time)
I'd love if you could do a friction comparison of the different options, perhaps by comparing clean vs dirty bolt velocities with standard milspec, lightweight, and possibly different coating types. I think that'd play a bigger role, perhaps pushing users towards a heavier buffer and cutdown BCG for better reliability than milspec. Or if the friction really doesn't matter, in which case the cheaper lighter buffer and milspec BCG are better.
I recall competition shooters complain about occasionally outrunning the bolt on semi-auto, pressing the trigger too early and having the hammer ride on the back of the bolt causing a light strike. You are lowering rate of fire with lightweight bolt if you balance the gas system. Another issue is using 556 as part of NATO alliance: the 556 has a range of pressures allowable as well as bullet masses. Your rifle has to run with excess bolt energy most of the time to use them all reasonably well and Ukraine has shown that some rifles are picky about the country of origin of their 556.
10:38 Reminds me of when I tried to pull start my snowmobile engine without the clutch (basically the engine’s flywheel/part of the CVT belt drive, the clutch easily doubles the engines rotating mass). It was impossible to overcome the compression stroke without the additional mass of the clutch helping overcome the compression stroke with inertia.
This is an interesting way to make AK rifles(especially 7.62) lighter shooting but to make it truly function requires tuning the size of the gas port, the strength of the spring, and various other things.
You're missing the foward force that happens when the BCG is launched backwards. Which somwhat cancles out the recoil from lauching the bullet A heavy BCG can be very smooth shooting if it can decelerate with long traveling distance. Like that of the Ultimax 100. But most rifles don't have very long receivers to accommodate this. So with a nomral length of travel, a lighter BCG would have less momentum when it hits the end of the receiver
Yup. The recoil behavior of a gas operated gun involves the rearward impulse from the bullet when the bolt is still locked, the forward impulse on the front wall of the gas system, the rearward impulse transferred through the recoil spring when the bcg moves back, the rearward impulse of the bcg striking the back of the receiver, the rearward impulse transferred through the recoil spring when the bcg is pushed forward, and the forward impulse of the bcg striking the front of the receiver. But I was not ready to do all that math at once and compare them as a function of reciprocating mass, so I just swept most of them under the rug lol
The recoil impulse is the same.. When used in a constant recoil system, it spreads the force over a longer period of time instead of all of a sudden when it impacts the rear..Constant recoil was first seen by Sullivan and Stoner in the German STG44 (MP44)..@@cabbage6015
What many people don't understand is a heavier buffer's effect on dwell time (bolt unlocking) is insignificant..This was proven years ago by Colt and recently by SilencerCo' testing with a high speed camera and computer..A heavier buffer does have an effect on carrier velocity..The extractor will lift completely off the case rim (after) the bolt un-locks..It is the residual pressure that holds the case against the bolt face that allows the extractor to lower back down to perform the extraction process.. The hotter the chamber becomes the hotter the brass case becomes and the longer it will take for the case to relax (objuration) to occur..This is why carrier velocity is so important to reliability..A heavier or lighter recoil spring can have the same effect as increase in the operating mass..
I think it's nonsense what you're saying about dwell time because I've never heard anyone talk about BCG mass as a primary factor in dwell time. Some people might have a wrong idea what dwell time is but that's not the point.
Interesting. I think I read somewhere (probably Sturgeon's House) that the residual chamber pressure after the bolt unlocks contributes a fair bit to the bcg's kinetic energy going rearward, and also makes the extractor lift up like you said? I wonder if this behaviour is unique to AR-15/AR-10 pattern rifles where there is little to no dwell time built into the geometry of the bolt carrier's cam track, as opposed to AK pattern guns where there's like 10mm of bolt carrier travel before the bolt starts to unlock?
The dwell time is from when the bullet passes the barrel gas port to the time it leaves the barrel..It is the straight part of the cam track that effects the residual pressure..LMT increased the straight part of the cam track to allow more time for case (objuration) and it work perfectly in the M4 platform..The reason the military did not adopt it was because it would not work reliably with the rifle length gas systems and it would have required supply to carry two different types of carriers..The extractor lift study can be found at AR15 repository..The test was done by the military TATCOM (Understanding extraction lift in the M16 family of weapons)...@@cabbage6015
@@hairydogstail I think in your first comment you mix up dwell time with lock time. But explain dwell time well in the reply. I've found through my own amateur experimentation that buffer mass does effect lock time, it's only logical that it does. However what's actually key is the ratio between the mass of the carrier and the mass of the buffer. The higher the buffer mass in relation carrier mass the more effect it will have. The reason for this is that even on a standard cam track there's still a time when the carrier is moving back without rotating the bolt. The movement of the buffer mass slows that initial movement.
I wonder if this has anything to do with the ratio between the mass of the bolt itself vs the mass of the carrier. Because altering bolt carrier mass while not altering the bolt mass will result in reduced rearward kinetic energy after the bolt is picked up after the unlock process. Iirc the fw army ordnance manual talks about a ratio of 3:1 for ideal carrier to bolt mass ratio. So there might be something there ig. Lighter carriers also require stiffer springs as seen in the foxtrot mike bufferless carrier uppers, which makes charging more difficult. Maybe a reason they went with the forward charging mechanism. Just a few thoughts ig.
The only issue I had with the enigma was taking it off. My work around to leaving a gun in my vehicle was to carry another holster. I carry a custom IWB holster and move my pistol to that if I need to leave it in my vehicle. If I need to take off the enigma in public, I don’t need to worry since I placed it in another holster. My leg strap has never disconnected on me. It’s defiantly operator error.
Never forget, if an informative video seems too long or boring, turn on captions and put the playback speed at 2x, you consume more video in less time :D
This may be a tedious or insufficient request but could you possibly make your following videos louder by chance? I'm a little hard of hearing but love the content. Also larger letters would he an absolute delight as well. If it's too much then ignore me entirely, my feelings won't be hurt but I will cry in the shower after that
One other major factor with mdr issues you hear of is caused when used with 25 round pmags in 308 there is an early release and uncontrolled feed when coming from the right feed position on all the variants of that mag from full cap down to 10 rounds once it’s down to 10 remaining the feed from the right position works perfectly the left feed position has no issues at all for the entire mag
I think an explanation for why the energy is the same in the two configurations is warranted: The lighter Bolt Carrier System has the same force(F) from the gas cylinder(because piston cross sectional area and gas pressure are the same), but its lighter weight make it accelerate(a) twice as fast, but since the stroke distance(s) is the same the force from the piston is therefore acting for a shorter period of time, hence the final speed is not twice, and energy is therefore the same. (a=F/m), (2*a*s=v^2)
Peter Kokalis used to make a big deal about the Bolt carrier to Bolt mass ratio. I presume he'd read the US Army Weapons Command’s 1968 “Technical Notes: Small Arms Weapons Design” and gleaned that from it.
Peter Kokalis was the go to guy back in the day..Many of his discoveries were lost with modern firearm writers such as the AKM's 5 piece (so called rate reducer)..It is not a rate reducer but an anti-bounce device..
@@hairydogstail I always enjoyed his writing. It really sparked my interest in small arms technology. That bolt to bolt carrier weight ratio seems to have been forgotten or cast by the wayside too.
Right near the start I question the assumption of equal kinetic energy imparted; I would be curious to know how different the result may be if equal momentum is assumed. Equal moment impulse may be the more accurate assumption, or at least something part way between fixing energy or fixing momentum. This is because the initial gas charge is based only on barrel pressure and time from the bullet passing the port to exiting the barrel, and that kinetic energy transfer comes from force and distance while momentum comes from force and time. The restriction of the gas tube is likely substantial in the analysis, and the time of bullet in the fast end of the barrel (port to muzzle) is likely much less then the one directional travel time of even the lightest bolt carrier. This of course depends on the dynamics of the initiating gas pulse, specifically how it dissipates both the static and dynamic gas pressure from a shot.(and assuming semi-auto so the time between cycles prevents direct pressure wave interactions. (Residual heat in the parts effecting conductivity and part clearances would be the only interaction of one shot on the next). As far I know no common designs use a checkvalve so there would be more loss of pressure back out of the gas port with a heavy slower mass. How much backflow likely involves timing of pressure waves not unlike tuned header pipes or expansion chambers(2 stroke) on a piston engine. If backflow loss is substantial then equal momentum is almost certainly a better assumtion than equal kinetic energy. I have not calculated the relative cooling effect on the gas charge due to expansion vs conduction to the gas tube, piston, and cylinder. If conductive cooling is proportionally significant than the slower heavy bolt will also have more pressure loss from a given amount of hot gas and again tilts toward equal momentum.
12:53 The WLVRN is definitely a promising design, but that inconsistent ejection pattern (provided the ammunition was quality controlled) looks like a bit of an issue. There are so many possible causes that saying anything is most definitely being an armchair-gunsmith, but seeing as they had issues with it on the MDR, I'd be interested to see if they properly upgraded the ejector spring to compensate for the change in BCG momentum when going with the heavier BCG; at least when a loaded magazine is exerting a force upward on the BCG (as the first rounds eject forward, and progress rearwards as the magazine nears empty). Definitely looked like something was going on there.
I see this "debate" go on in forums, whenever it comes to "tuning" their rifles. I will admit, i enjoy tuning and optimizing myself but i always try to prioritize reliability first and foremost. What are your opinions on messing with spring strength meanwhile then? We often see lots of mentioning regarding the BCG and buffer masses as they are the reciprocating bits of the AR, but there really has been an increasing proportion of folks going into stronger springs to take the role of or compliment these buffer weights now. I am seeing some folks preferring to make up for the lack of a buffer weight with a stronger spring instead (so instead of perhaps a carbine spring with an H3 buffer, i would see them using a 15% XP "blue" spring or even a 25% XP "red" spring with an H2 buffer or lighter now rather). Assuming a full mass BCG still of course.
I haven’t thought about that too much but it seems like a good idea since you’re not reducing the energy provided to the bcg by the gas system. A stiffer spring will absorb more kinetic energy during the rearward stroke, so the bcg will bottom out with less force, but the flip side is that it will give more kinetic energy to the forward stroke so the bcg will hit the barrel extension harder. But I guess a heavier buffer would do that as well, and it doesn’t have the added reliability benefit of a stiffer spring. Another thing is that the extra kinetic energy forward may or may not lead to more bolt carrier bounce, but that’s probably a non-issue in semi auto
Spring will not make up for buffer mass, they have a different roll. I can see a place for a heavier spring with full mass systems, but not with low mass systems.
In this example from the original commenter, velocity of the bolt carrier will increase (your thoughts on forces can be equalized if the reduction in mass and increase in velocity end up at the same force). The only concern I see if this approach is taken to far is the magazine may not be able to present a new round in time or the extractor may not new strong enough to not “bounce” at the wrong frequency and slip off the case head.
The only way that you can possibly help the light carrier problem’s (that is failure to feed or failure to chamber rounds all the way) is to add a *bigger* buffer weight and with longer weight travel (meaning a longer buffer). But that would only bring you back to square one by adding more weight again.
What doesn't make sense to me then is that you will generally notice a fairly obvious decrease in felt recoil when using a HEAVIER buffer. You can try it for yourself. Take any off-the-shelf AR-15, they will normally be over-gassed with a standard carbine buffer (~3 oz) to ensure reliability in cycling all types of ammunition. Swap the buffer for an H1 (~3.8 oz) or H2 (~4.6 oz) buffer, and you will normally see a noticeable decrease in felt recoil. The weight of the buffer will be the only factor that has changed. Why is that? It seems contradictory to what you explained here. Not trying to say you are wrong or anything, just curious and would like to understand more.
And what top 3 facts about them which the broad masses of the people don't know? And do delayed blowback (lever or roller) systems have future and benefits over piston operated and short recoil systems?
Can you make a video on the A5 buffer system? I always go with A5 just because people say it's better than carbine, but I really don't understand why a rifle spring is better.
I very much suspect that the standards of springs and cartridge rims in ars were made without the assumption that bolt carriers will get this much lighter and that is likely the cause of the mentioned issues.
Well, not exactly. Springs need to be tuned-just like gas or a BCG. Too strong a spring, you’ll either fail to extract or your BCG will slam into the front of your gun. Too weak a spring, and you’ll run into the same issues the video mentioned-bolt slamming into the buffer tube, stripped extractor, etc. Ig in the context of making a reliable AR15, a strong spring is good. Competition shooters tend to lighten their springs.
@@noahchong9130 yeah obviously I don’t endorse just throwing the strongest spring in there right off the bay. But tuning it with whatever is the right strength. Just like how we don’t go straight to h4 buffers
6:26 Im pretty sure the force should be the same in both. You said it yourself, the cylce rate is faster with a lighter bcg and so immediately its obvious that time cannot be the same for both in the momentum eqn . I think the fact the Bcg is traveling back and snapping back forward again is what is causing the “lighter recoil” feeling. “Recoil” isnt just the first half of momentum, its the equal and opposite forward momentum as well
FOLLOW UP:
I'd like to use this pinned comment to expand on some of the details that I glossed over/missed in the video. A lot of these details are contributed by thoughtful commenters, which I really appreciate!
1. Please keep in mind that the video is talking about the reciprocating group as one mass and ignoring the interaction between the different components. I wanted this video to be applicable to gas operated firearms as a whole. Here are some of my thoughts about the quirks of the AR platform if you're interested: The buffer doesn't contribute kinetic energy for unlocking, bolt pickup, and overcoming any friction/forces that resist solely the bolt carrier during the rearward stroke (e.g: hammer spring force). However, it does help everything in the forward stroke. A few commenters mentioned lightening the bolt carrier but increasing the buffer weight as a method to soften the felt recoil. This works because even though the overall reciprocating mass is the same, a larger portion of that mass is now in the form of the movable buffer weights, which spreads out the impulse of the reciprocating mass over a larger amount of time. The flip side is that the lightened bolt carrier now has lower kinetic energy to overcome the previously mentioned resistances during the rearward stroke.
2. Is it reasonable to assume that both reciprocating masses takes the same amount of time to come to a stop after bottoming out (5:23)? This amount of time is dependent on a few things like the stiffness of the buffer material, the butt pad, and how stiff the shooter is holding the gun. Additionally, the impulse transferred to the gun when the reciprocating mass bottoms out is also dependent on the rebound velocity after it bounce off the rear of the receiver (after removing the contribution of the recoil spring). I could not find a way to account for all of that, so I made an over-simplistic, catch-all assumption that the impulse time is the same, and did not include the time after v=0 into the impulse time. This is for the sake of being able to compare the impact force, which I think is more intuitive to understand. The more accurate thing to do would be to just stop at comparing the impulses of of the reciprocating mass striking the receiver, where the impulse could be understood as the capacity to apply a force over a length of time.
3. Another over-simplistic assumption that I made is that the gas system provides the same amount of kinetic energy to the reciprocating group regardless of mass (1:45). The amount of KE provided by the gas system is the mechanical work done by the propellant gas on the reciprocating mass. This can be calculated by taking the integral of the force applied to the working surface of the gas piston over the distance of travel during which the piston is pressurized. (Note: in the AR-15, the "working surface of the gas piston" is the rear surface of the gas chamber inside the bolt carrier). In the video, I compared a gun with standard gas and standard mass to a gun with standard gas and low mass, so I assumed that the gas system has enough pressure to apply roughly the same force during the entire pressurized stroke of the piston. However, if you use an overly heavy reciprocating mass for a given gas system, an interesting thing starts to happen. The pressure inside the gas chamber drops over time as the bullet goes pass the gas port and exits the muzzle. An overly heavy reciprocating mass will accelerate very slowly, which means the gas pressure can drop significantly during the pressurized stroke. Therefore the force-distance curve of the piston will drop, the area under the curve will drop, meaning the kinetic energy provided to the reciprocating mass by the gas system will reduce. TL,DR: In real life, if the reciprocating mass is too heavy for a given gas system, you can reduce the amount of kinetic energy provided by said gas system, and the gun might short stroke.
4. Another obvious, but implicit assumption I made in the video is that in both guns, the reciprocating mass bottoms out on the back of the receiver. This is true for most military weapons. If you tune the gun so that the reciprocating group does not bottom out, then it categorically changes the recoil behaviour, and the math I used no longer applies. What would still apply is that an overly lightweight reciprocating group would still decelerate faster, and you would still have a harder time balancing a slow enough initial velocity for extraction, and fast enough to complete the cycle. If you want to know more about cases where the reciprocating group does not bottom out, then patent US4475438A is a good read. It's Jim Sullivan's patent on the constant recoil system. And it's more complicated than just making the reciprocating mass not bottom out.
5. A viewer brought up an interesting detail about the AR platform. During the extraction phase, after the bolt has unlocked, the extractor momentarily lifts off the rim of the fired casing. It is the residual chamber pressure after unlocking that presses the case into the bolt face, allowing the extractor to fall back down and grab the case rim again for ejection. A few tests showing this phenomenon were detailed in a May 2003 US Army TACOM presentation, titled "Understanding Extractor Lift in the M16 Family of Weapons". Supposedly, the implication of this is that the initial BCG velocity is important because if it's too fast, the BCG recedes faster than the residual chamber pressure can press the case into the bolt face, leading to failures to extract.
Are u talking Arizona to Alaska as in temps
@@syitiger9072 yup
US ordnance (the government) found that, to have a reliable selfloading firearm, you need a Bolt carrier:Bolt mass ratio of about 3:1 or greater. the greater, theoretically the more reliable.
SCAR17 is at 8.8:1. M1 is at 1.75, M14 is at 1.45. This is very low, but the M14 doesn't lose much relative to the M1 for that loss. It's more that they would gain a lot of energy retention from getting to 3.
AR15 has 4.68 for a full auto normal Colt BCG.
K1 has 5.88
AKM is at 5.4
Thank you for an outstanding video and follow-up clarifications! While I agree there is more to Constant Recoil than simply keeping the bolt from bottoming out, that is a huge benefit unto itself. Many commenters on videos about Constant Recoil claim that it would be useless or have no effect in semiautomatics. That's like saying that switching out your dirtbike's long-travel springs for scooter suspension would be equally controllable or comfortable on a rocky trail. The effects of inadequate free recoil travel are readily apparent in subcompact pistols. Not only is recoil worse, but the springs are much stiffer (offer more resistance during the critical ejection portion of the recoil stroke) to avoid it being MUCH worse.
"Is it reasonable to assume that both reciprocating masses takes the same amount of time to come to a stop after bottoming out". No, a more reasonable assumption is that the effective spring constant will be the same, which means the heavier mass will apply force for longer (but still more force). As you say though, just compare impulses.
More importantly though, the BCG slamming into both ends isn't the only impulse -- there's also the impulse directly transmitted to the receiver through the locking lugs. Pump action shotguns don't have *any* recoiling mass when fired, while semi-autos do and this makes them softer shooting. This is because the direct impulse is lessened, and then spread out over time with the recoil spring.
"Another over-simplistic assumption that I made is that the gas system provides the same amount of kinetic energy to the reciprocating group regardless of mass". This is another incorrect assumption. It's more of a fixed impulse, and heavier BCG will have less energy for that same imparted momentum. This is why decreasing the mass makes it overgassed unless you turn the gas down to compensate.
Other than that though, I think it all checks out
For those who are truly passionate about small arms, there is no other content like this on youtube, period.
A viewer recommended a channel called "Konstantin Konev" to me. Dude's an actual firearms engineer, worked for LMT. His channel is an absolute treasure trove of firearms knowledge. The only thing is that it's all in Russian lol
@@cabbage6015 Well time to learn more than just swear words in Russian.
This is the only math lecture I've willingly sat through
Amen to that
This is one perfect example of, what is good for competition, is not always good for military use.
Do they use full auto in competition?
@@ipanzerschrecku4732to be fair full auto isn't even really used in the military unless you are just burning ammo after a range. Soldiers are taught to prioritize accurate semi auto fire to increase accuracy and conserve ammo.
Russians are pretty much always firing full auto bursts with their AK74s
Western militaries typically are firing semi auto though.
@@nemisous83 Frankly it sounds to me that you have absolutely no idea what mode of fire "a military" uses or have any clue what you're talking about. You're just regurgitating something you've heard somewhere taking it completely out of context and you're just the guy that chimes in with something stupid without making much sense.
@@nemisous83also full auto fire power is very effective in gaining fire superiority and suppressing the enemy hense why a modern day infantry squad is built around a GPMG where the individual rifleman can substitute fire and movement. You literally have no clue but you felt the need to chime in with a know it better attitude built on pure ignorance regurgitating something you've heard somewhere about a very specific scenario for a tiny tiny little group in the military of special forces soldiers and even then it's garbage because those very same groups use extreme amount of firepower to get out of trouble if need be using massive amounts of full auto fire if ambushed for example.
Years ago, I was really, REALLY into high performance paintball guns. One thing that we learned was that low reciprocating mass was preferred, but as the mass lowered the cycle speed would almost invariably increase. Adjustable gas regulators could tune in the gas pressure and a solenoid valve would handle volume. With these two parameters, we could better control bolt dwell time. Often though, thr smoothest shooting guns had the lightest bolts, and the LOWEST FRICTION design. Friction was the hardest thing to overcome when trying to achieve a smooth shot cycle. Something to think about in your next AR build.
It'd be interesting if we start seeing "low friction" BCGs and uppers with less/smoother contact surfaces to reduce felt recoil.... or are these already a thing for competition?
Already a thing, they're called "enhanced" bolt carrier groups. @@zeronamenata4757
There are "enhanced" BCGs with low friction coatings and sand cuts in the bearing surfaces.
That's why my ARs get disgusting amounts of lube & grease (yes I use both)
@@calebnation6155 same here, grease for the sliding parts and oil for the rotating parts. Most people don't grease their cam pins but I think it's very important to prevent wear in the cam pin channel as well as to help dampen the forces on the cam pin during cycling.
9:36 "The light weight BCG and it's consequences" lol
Rip uncle Theodore
Horrible example though, No buffer. So then it's on the manufacturer to make sure it's suppose to work on most AR setups.
I believe the gun should fit the time-place-occasion, if it's supposed to work in many different conditions, eliminating variables with a heavier BC is a good idea, but if its a competiton gun that doesn't fire full auto and only semi, i think there is a decent trade off to be had with a lighter BC
Agreed
For non-match guns, I like to run the heaviest buffer I can get away with for just that reason.
Also keep in mind the heavier, mil spec carriers will lost a lot longer than lightweight units.
You are the kind of person I’d like to work with in physic lab. Solving things symbolically makes me happy
very good and informative video...and i've been using the AR platform since 1987.
I'm an engineer by trade and can confirm your reasoning and math checks out, and your assumptions are reasonable. I love content like this keep it up!
I think one difference is that the amount of kinetic energy added from the acceleration off the gas piston would be less for the lighter one. The length of the gas piston is fixed, and would spend less time accelerating on it due to accelerating faster and traveling that fixed distance sooner.
Well you failed
As a senior in MechE who is also hoplophile... so happy i found this channel
In depth discussions like this are great for the community in my opinion.
Great video. One point to contextualize Sullivan's comments in Ian's interview that he would rather increase the mass: his point of view centers around full-auto firing. As you point out, there is an impulse when the reciprocating components bottom out (often referred to as secondary recoil) as well as an impulse when the reciprocating components go into battery (tertiary recoil). Primary recoil of course is caused by the bullet being accelerated downrange. From the perspective of the shooter when firing full auto, tertiary recoil from the preceding round occurs contemporaneously with primary recoil from the successive round. As these impulses are in opposite directions, they can nearly cancel out in a well-tuned system if that is one of your design goals, as it is in some of Sullivan's designs that came after the AR15. Reducing the mass of the reciprocating components drops the momentum they have when entering battery as you point out, and thus reduces the tertiary recoil impulse that would cancel out the next primary recoil impulse. This is why Sullivan thinks it's crazy to reduce the mass: it's counter to his design goal of "constant recoil" under full-auto fire. Of course, if you have primary and tertiary recoil working in harmony you haven't necessarily done anything about secondary recoil. Sullivan's modification to the AR15 design also incorporates a carrier designed for a longer stroke, with more wiggle room in the travel distance between bottoming out and being able to strip a round from the magazine. This allows his system to be tuned to never bottom out or at least not do so heavily, where the reciprocating components are halted in their rearward motion primarily via friction and spring pressure over a longer duration. In this situation, the push the shooter feels is simply the pressure the reciprocating components apply via the spring and friction, which does oscillate but with a much smaller delta than a system where the moving parts come to a sudden stop. With secondary recoil minimized, the weight of the reciprocating components is no longer an issue there and they can be made heavier to help the tertiary recoil cancel out primary recoil in full-auto, which is exactly what Sullivan has done. The system can now be said to be in a state of "constant recoil" for marketing purposes. Sullivan's AR15 design modification for "constant recoil" was commercialized in the form of the Surefire OBC.
Holy fuck you weren’t kidding about the nerdy lol
I won't pretend to understand the math if not dumbed down by him, but it's good it's there I suppose showing his method.
Once again sir, you killed it. This is one of the most informative video I've seen. Keep up the good work sir.
Thank you!
Absolutely loved the vid. Really rare to see people talk about the math and physics behind guns with detail.
Thank you for pointing out the importance of the ratio of bolt weight to reciprocating mass (bolt carrier + buffer). Early in the development of the AR-10 the bolt carrier and buffer were a single part. A reduced weight buffer would be a lot cheaper than a reduced weight bolt carrier.
Bro I had been doing so much digging on the internet for stuff like this! To theorize a perfectly tuned “felt-recoil free” service rifle, I even resorted to retaking online physics lessons.
Thank you so much for putting out this video!
Please make more content like this I thought I would be bored but I came out smarter and more informed on not just the pros and cons of weights of BCGS but a little bit of trivia on another weapon system
Great video.
It would be nice to see a video with calculations for a "properly optimized" system used for 3G guns.
Should be very helpful to understand how much "round stripping" and "bolt bounce" are affected and if it is really an issue.
Anecdotally, the following values work flawlessly on many guns, various calibers/loads and environmentals:
1. GAS port restriction: 40% (estimation)
2. BCG weight reduction: 30% (-4Oz)
3. Buffer weight reduction (reciprocating part only): 80% (-2.4Oz)
4. Recoil spring strength reduction: 10%
Good video. I think you pretty much covered all angles of this issue. It's all about maintaining adequate spring work and momentum on feed within the range of mechanically optimal velocity and magazine safety time.
me watching guntubers: fun and gigles, but i learn little.
Me watching this: here, now, this is the goat. the kind of content i was searching.
This is the kind of nerdy stuff I enjoy! Thank you!
Thank you for sperging out, this was very helpful.
Sick video. Awesome job. Please post more content like this. Maybe something on spring forces and how they interact would be great or about gas pressure, etc.
Great video, explains everything I need to know about buffer weights and such.
Thanks for the video. I don't understand every bit of it, which presents a welcome challenge.
If you look at the A5 system, it is designed to allow for more weight and a higher sprung carrier as it gives the carrier more "oomph" to trudge through any debri and get you solid bolt closing.
Makes sense. Not to mention, you can run into bolt bounce issues with improper tuning.
I've been using the A5 system for nearly 15 years. It works. 💯
The only real advantage is the amount of weights that can be used compared to the carbine system..
@@hairydogstail Incorrect.
What is incorrect??@@DBravo29er
The largest advantage of the A5 system and its copies isn't its ability to have more buffer mass, it's the biasing of the buffer weights and the use of a longer recoil spring for the same stroke (no, despite what you learned in high school Hooke's law is not a complete descriptor of spring behavior)
wow thank you so much. i had been very confused about how buffer weights affect the gas system and couldnt find a good answer. this was great!
Love this kind of video. Great nerdy deep dive into guns. Keep this up!
Fantastic video. I think this is very helpful for explaining the “tuning” process of an AR, by altering Gas, Mass, and Spring. I think more videos diving into the other variables to find ways to either minimize recoil, maximize reliability, or increase the operating envelope, would be very valuable.
Caleb from brownells noted on MAC’a Aric video that it looked like it was installed incorrectly. There’s also a break in period.
Yup. The plug was likely binding
Great video and it helps explain why I ordered that lightweight BCG for my subsonic 300BLK build since the F is inherently lower to begin with so I don't get the negative effects of lower m.
[Update: And it works!]
If you add a stronger recoil spring to counter the increased velocity, then adjust the gas for reliability, you can increase reliability over the lighter bolt carrier by itself. You are essentially trading bolt mass for bolt velocity to maintain reliability.
This content is amazing. You definitely earned my subscription.
Out of curiosity, would having a stronger spring plus more gas coming from the gas block help solve this issue? I don't know too much about guns so there might be some problems with what I'm thinking.
Part of this is the ratio of weight of the carrier to bolt , IF you look at one of the design changes made to the AKM to AK74 , you will see a lighter weight AK74 bolt ( the stem is reduced diameter ) , this gives the AK74 higher carrier to bolt weight ratio , to give the bolt more force in chambering/locking , my the higher mass ratio .
Great examples of this Bravo. I run a 2A Armament titanium bolt carrier that has a gas adjustable feature on the bolt carrier itself. I run it with a Geissele super 42 buffer spring and an H3 buffer. Once I dialed the gas in its absolutely flawless and insane smooth. Just my 2 cents worth.
A milspec BCG is about 11.6 oz and a standard CAR buffer is about 3.0 oz for a total 14.6 oz or so. I did similar with my WWSD build, getting a Faxon Gunner lighweight BCG (8.5 oz) and H2 buffer (4.6 oz) for about 13.1 oz total recip mass, shifting the COG a little rearward. Reliability has been great, seems like less friction from having less surface area.
love everything your saying and i also have seen all the interviews/videos and such my irl gun is a m16a1 with muzzle break and 9oz bcg and its 100% recoiless i actually want to design my own bcg that is ultra light
Great vid. A not insignificant difference with changing reciprocating mass is time in battery. Obviously most of us can’t calculate the difference but it can be quantified through performance and it should be considered.
As someone who has built two AR's with titanium BCG and lightweight buffers, an adjustable gas block is 100% needed. My picks are either the Riflespeed or Superlative Arms. I haven't used the Riflespeed but it seems very easy to adjust, although it seems to have less adjustment and no bleed-off like the ones from superlative arms. Reliability is really only an issue if I run lower pressure .223 rounds, but with that said 1-3 clicks to open the gas block fixes that. Also these AR's are ran suppressed, the Superlative Arms bleed off really shines here as most excess gas is bleed off at the gas block and not at the BCG, so less gas in your face.
Fair assertions.
To simplify the math all down to one sentence: Newton's laws of motion tell us all we need to know (particularly the 2nd and 3rd laws).
Speaking on the lightened bolt carrier subject, I have a WWSD2020 I personally tweaked to be as light to carry, and as light recoiling as possible - within acceptable parameters. It comes with JP's silent captured spring, which has adjustable springs - I put the heaviest one in there. I changed the bolt carrier out for a low mass BCG from Brownells. I put on a Superlative adj. gas block with the correct gas journal. Then I tweaked the gas a handful of clicks above cycling flawlessly with low power .223 ammo.
What I sacrificed in reliability, I gained in performance and weight savings. As a civilian, that's an acceptable trade.
Привет, классное видео , кое что новое я услышал про вес затворных рам ,могу отметить что решение с газ регулятором достаточно сомнительное , есть смысл ставить газовый поршень (кучность слегка упадёт) .
Hello, cool video, I heard something new about the weight of bolt carriers, I can note that the solution with a gas regulator is quite dubious, it makes sense to install a gas piston (the accuracy will drop slightly).👍👍
When I ran lighter BCGs in my carbine style AR10s, I knew it would increase the velocity of the BCG, which in turn would cause additional wear on the hammer, buffer spring, buffer and eventually the BCG itself. So when using one, I've always used them in conjunction with a slightly stronger buffer spring and a hydraulic oil piston buffer to nullify the negative effects.
Great video! I'm curious to see what you think of the Foxtrot Mike FM-15 bufferless uppers. These also use a modified shortened carrier, but from what I've heard are far more reliable than the ARIC Bufferless BCG.
Good video. Though, I’ve got to rein in my expectations on “nerdy”. I was expecting stress analysis and fatigue life on different bolt carrier groups comparing different materials.
Great nerd talk.
Another thing to add, militaries also have full auto. Which makes bolt carrier bounce and high cyclic rates a bigger issue and also favors heaver setups.
And the DT Wolverine, so basically MDR generation 3, seems to have some magazine locking issues. Time to wait for the gen 3.1 hot fix in a month or two from now.
6:36 this conclusion was satisfying to watch .
The "problem"/best point of this video is the "fair" comparison. For high level competitive shooters, they do not just make a single change, like a lighter BCG; that is just one of MANY major upgrades they make. This is a problem, as it doesn't reflect the complex nature of the total modifications made; however, it is the best point in that thinking you can just change out a lighter BCG and your gun is going to be just as reliable is not realistic. To expand on that, high level shooters also do TONS of testing and tweaking parameters to tune their equipment precisely; they don't just buy upgrade parts and slap them in, as most people think they can. Ammo is a VERY important factor; competitive shooters require much more precise ammo than most people, and are tuning the rifle to generally just 1 load, which is the only load they shoot out of the gun ever. Factory guns are designed to work with any ammo that falls within SAAMI specs, instead of only one load. Reduced recoil spring pressure is great, so long as you clean the gun after every match, keep it clean during the match, and if it's dusty out then you open it up and wipe it out between stages! Competition race guns are amazing and blazing fast; however, they require much more maintenance, are not quick or easy to set up and tune, and are not reliable with a wide variety of factory ammo.
Great vid! BCG mass and carrier to bolt head mass ratio are often regarded as some of the more important factors when it comes to reliability.
I have a few questions on the topic of recoil tho, given a certain BCG mass.
Over the years of watching gun videos on youtube I have heard comments saying that "snappy" recoil is better for semi, and constant recoil doesn't do much for semi. On the other hand, I've heard ppl say the 556 MDR and the RDB have low recoil due to their longer than usual (but not quite constant recoil level) recoild stroke. Which one in your opinion is true?
I think it's mostly coming down to personal preference. It goes back to the impulse equation at 4:55. Assuming the initial BCG momentum is the same, if you have a slower recoil cycle like the MDR and RDB, the time increases and the force reduces. Opposite is true for a faster recoil cycle.
When I shot low powered .223 in my X95, the BCG velocity is slower, and it feels like a gentle push. If I switch to hotter 5.56 then it's a quicker but harsher snap. I can see the pros and cons of both cases. A gentler push doesn't knock my sights off target as much, but the recoil cycle is slower and my sights are off target for longer. A quick snaps knocks my sights off a bit more but it also goes back on target faster.
I'm gonna say it depends a bit. I've had more trouble tracking sights with some snappy recoil, but "pushy" for lack of a better term, you can keep a better sight picture and just push it back on target. I'd say it all comes down to how much total recoil you're going to see, whether getting it over with fast vs spreading it out is going to be a better strategy.
In 5.56? Quick snap is probably going to be better, because total recoil is really low. .308? Might want to spread that recoil out a bit. A snappy 12 gauge? No thanks.
I have a 3" barrel .44 Mag. It's the extreme of "snappy" recoil. The gun is just suddenly in a different place. It'd be a lot more controllable as a longer push.
This is the type of content I look for.
The amount of velocity/energy that the rebound of the reciprocating mass gives to the return to battery stroke is non-trivial. It's based purely on velocity; faster cyclic rate (rearward velocity during spring compression) increases the amount of energy returned via the rebound off of the far end of the receiver extension.
Also, just run an FA carrier and use the Vltor A5 system. 👍
I did make my math a bit oversimplistic when I only looked at the length of time between the bcg bottoming out and coming to a point of zero velocity. I didn't know the equation for rebound velocity (or if there is an equation), so I just swept that under the rug for the sake of having a clean impulse equation with the same end point lol
@@cabbage6015 I think you did a superb job and would love to see you dive even deeper in future videos. I would have made the same decision you did. Keep it up!! 👍☺️
@@DBravo29er Thanks for the kind words!
Ive owned every MDR generation and am very familiar with its changes and drawbacks.
Youre right about the light carrier problem, but another issue that plays into this whole tuning dynamic with gas operated rifles is the location of the gas port and the geometry of the bolt carrier cam path.
Desert Tech chose to rectify the rim ripping issue, present only in the 308 rifles, by increasing the size of the extractor along with modifying the gas plug.
Moving the gas system further from the chamber, or by lengthening the cam path helps reduce the ammount of energy needed to cycle the weapon as well by allowing chamber pressures to drop to lower levels at the time of extraction.
Imo changing the reciprocating mass should be one of the last variables you address when tuning a rifle, whether that be for duty or competition.
Subscribed, because we need more of this. I think more reciprocating mass should be moveable buffer as opposed to solid. Per my understanding/guess, the moveable buffer mass essentially does the positive things that solid mass does, but requiring less mass.
Maybe the initial part is a little worse - the unlock has less mass, of course, but you should get a little delay/slowing at the end of the travel due to the moveable mass, and then of course, it should also help the forward motion back into battery.
I’ve wanted to test a heavy buffer and lightweight carrier for a long time, ideally ending up a few oz lighter than a standard system, but haven’t had time.
What are your thoughts? Why am I wrong?
I think it's a good idea generally.
Moveable buffer weights spread out the impulse of the reciprocating group striking the rear of the receiver extension, because instead of one large mass impacting at once, it's multiple smaller masses impacting throughout a larger length of time. It works to kill bolt carrier bounce too, but I guess that's not too important in semi auto. If the total mass is the same as a solid reciprocating group, it will store the same kinetic energy to overcome springs and frictions, so yes it retains most of the benefits of the same solid mass. There's just one quirk which is the buffer mass does not help the unlock and pickup of the bolt, only the carrier mass does, but unless one doesn't go overboard in reducing carrier mass it should be fine.
The only thing I might not agree with you is when you said moveable buffer mass does the positive things that solid mass does, but requiring less mass? I could be wrong tho
@@cabbage6015thank you - I meant *some* of the positives, such as improved delay at end of travel, allowing for the magazine spring to push up the next round, and then acting like a dead blow when feeding that round. Obviously they (free or semi free moving mass, and solid mass) behave differently.
The only thing I worry about is the initial unlock and velocity rearward, although that should be able to be addressed with adjusting the gas system.
Thanks for your input, hope you end up having more thoughts on the subject at some point.
A video on hydraulic buffers would be incredibly interesting. Cheers
The recipe for a reliable ar-15 with low mass BCG is to install adjustable gas block while retaining the stock buffer spring.
You tune the gas block so it ejects the brass perpendicularly from ejection port and the spring rides the bolt back in with enough energy to close the bolt.
Would you ever be interested in making a video about how muzzle brakes and compensators affect shotguns differently than rifles/pistols/etc.? The physics behind it are neat if you want something to dive into.
I wanted the lightest rifle possible and achieved a weight of 4.2 lbs without carbon fiber. The bolt carrier is skeletonized steel (Faxon), the buffer is a hollow plastic piece that weighs about a gram, and the recoil spring is reduced 10%. All of this necessitated an adjustable gas block of course, and it is set at 50%. The rifle also has an integrated muzzle brake. There's almost no recoil if you're shooting White Box, but the Tula steel cased stuff does introduce a bit of it as it is hotter. Despite minimal gas, the extractor does try to rip the rims off the cases it seems, although the damage to the cases is minimal. The reciprocating mass is just too light and the BCG needs the velocity to fully cycle. Another issue I suspect is occurring is bouncing at lockup. The reduced mass and spring weight may allow the BCG to bounce back slightly when going into battery, although I've had no malfunctions with this setup (except when I used way too much oil). I could fix both the bouncing and rim-grabbing issues by filling the hollow plastic buffer halfway with lead shot. This would give a deadblow hammer effect at both ends of movement and add a little mass back into the system.
It's important to point out that the LAW ARIC showed in the gun used by MAC was correctly installed, you can tell because the guide rods are too far forward when installed in the gun, they should be further to the rear of the cutout. This means the cup was not properly seated which will greatly increase the friction when it trys to cycle, leading to the issues seen in his video.
The amount of ke absorbed by the spring isn't the same, because the time it has to act is different. I would recommend looking at it in terms of momentum anyway.
At any given amount of compression there will be a certain force but the amount of time spent at any given force is longer for the high mass variant.
This can be derived intuitively by remembering that if the mass is too heavy in your AR, it will short stroke and never bottom out. Therefore, a mass that never reaches the end cannot have the same ke at the end point as a mass that does.
Mathematically when you bring out the impulse formula you're very close to being correct, you just should have applied it to the earlier part of the video.
∆p=∫f∆t and so an integral with the same force curve but stretched over a longer t will be a much larger area under the curve.
On the forward stroke you're correct though because the spring will be able to increase the p of the bcg more so a lightweight bcg will have less forward recoil, but more rearward recoil.
The rest of the video is spot on.
Overall I like the video a lot. I don't mean to be too hard on you, it's a good video and I'm definitely subscribing.
I really appreciate your comment, but I'd have to respectfully disagree. The elastic potential energy stored by a spring is given by E = (1/2)k(∆x)^2. It only depends on the change in length and spring constant, not time. No matter how long the mass is staying at a certain point of spring compression, the energy absorbed is the same.
What you mentioned about ∆p=∫f∆t relates to the impulse transferred from the spring to the bcg as it retracts, and yes that impulse does increase if the time is stretched out longer, but that's impulse and not kinetic energy.
The reason my calculation did not account for the case where an overly heavy bcg would short stroke is because of another assumption that I've made, which is the gas system provides the same amount of kinetic energy to both guns (1:45). Irl, the energy provided by the gas system can be calculated with the mechanical work formula, which in this case would be an integral over distance of the force applied to the rear wall of the internal gas chamber inside the AR-15 bcg (or force applied to the front surface of the gas piston on external piston guns). That force is dependent on the gas pressure, which drops over time as the bullet goes past the gas port and exits the muzzle. If the bcg is overly heavy, it would accelerate slower (F = ma), and thus the force over distance graph would drop more, the area under the force-distance curve will reduce, meaning less kinetic energy is provided to the bcg.
My assumption that the gas system provides the same kinetic energy in both cases does not hold up in reality if the bcg mass increases past a certain amount, and I missed that when scripting this video for sure. I've also failed to mention a few other assumptions, such as the the bcg will bottom out in both cases, which might not happen irl and will drastically alter the recoil sensation. Overall I do think myself that the math I've used is oversimplistic.
And no worries, I didn't take your criticism personally. Again I really appreciate you taking the time to comment, and I really love having in-depth discussions like this about my videos after I post them. I'm glad that you mentioning the case of an overly heavy bcg pointed out a mistake in my assumption about the amount of kinetic energy initially provided.
Really love what you're doing on your channel btw. I wish I can get a chance to tinker with firearm designs like that, but alas, the gubermint just banned the possession of firearms CAD files up here in Canada 😅
@@cabbage6015 Oops, I definitely got that ke part wrong, I started thinking about momentum and then wrote about ke. You’re correct that the amount of KE stored in the spring is determined by the constant and displacement alone.
The thing is, recoil isn’t a function of kinetic energy; it’s a function of momentum. The momentum of a system is conserved, so the bullet and gas going in one direction (with a certain amount of momentum) will be offset by an equal and opposite amount of momentum in the opposite (rearward) direction no matter what the recoil system or weights are. What we feel as recoil is this momentum being transferred from the gun to us, but there is no way to change the total amount of momentum transferred due to conservation of momentum. Even though the total area under the curve is unchangeable, the shape of the curve is and “Felt recoil” is more so the peak impulse, which we can change.
While the bolt is locked, the momentum is largely transferring to the frame of the gun alone (in a bolt action this is all that happens) but as soon as the bolt is in motion it picks up the remainder of the momentum and it’s motion rearward is slowed because the spring is transferring momentum from the bcg to the non moving reciprocating portions of the gun.
A heavier bolt will be locked longer, thereby frontloading the momentum transfer, but it will also give the spring more time to exert force, and the integral of force over time is change in momentum therefore it’s bleeding off more momentum which is why a heavier bolt is less likely to bottom out.
If the bolt bottoms out, it will dump the remainder of the momentum and this will typically be the peak impulse. The forward stroke also isn’t a function of KE, it’s a function of momentum where the spring acting longer is able to transfer more momentum into the bolt before it closes and causes the front of the gun to dip.
So the peak impulse is less with a heavier bolt, and the curve overall should be flatter and longer, but the forward momentum and dip of the gun will be more due to increased time to close the bolt.
I agree to conservation of momentum part, which is why I worded my conclusion as the heavier reciprocating group disrupts the sight picture more as is impacts the back and front of the gun, and not that it gives the gun a higher rearward momentum after the firing cycle is completed, because that would be wrong.
From what I understand from Jim Sullivan's constant recoil patent, in a gas operated gun where the reciprocating group bottoms out, there are 6 ways the rigid frame of the gun receives momentum throughout 1 complete firing cycle:
(1) The rearward impulse transferred to the rigid frame through the locked bolt as the bullet goes down the barrel
(2) The forward impulse transferred to the rigid frame by the gas pressure applied to the front wall of the gas chamber
(3) The rearward impulse transferred to the rigid frame through the recoil spring as the reciprocating group moves back
(4) The rearward impulse transferred to the rigid frame as the reciprocating group bottoms out on the back of the receiver
(5) The rearward impulse transferred to the rigid frame through the recoil spring as the reciprocating group is pushed forward
(6) The forward impulse transferred to the rigid frame when the reciprocating group strikes the front of the receiver
And yes, all 6 of these impulses combined will give the gun a momentum opposite in direction and equal in magnitude of the bullet and gasses leaving the front of the gun, as you said.
Among these impulses, Imo (4) and (6) are sharp spikes that disrupts the sight picture way after the shot is first ignited, and are influenced by the reciprocating mass, which was why I wanted to focus on them for the video.
I think your derivation of the rearward momentum as the BCG bottoms out is mistaken because the your impulse (1) is smaller than the impulse of the bullet, and if I understood you correctly, what you were saying is that (1) + (3) + (4) will equal the bullet impulse. You were missing (2), (5) and (6). According to Jim Sullivan, (1) should be equal to the negative of the bullet impulse. (2) is the impulse given by the gas to the front wall of the gas cylinder, and should be equal in magnitude but opposite to the direction of the impulse given to the reciprocating mass. (Later on the momentum provided to the reciprocating mass by this process will come back to influence the rigid frame as impulses (3), (4), (5), and (6)). As you said, a heavier BCG would accelerate slower, so the time that the gas pressure applies force on both the gas chamber and the BCG should be longer, leading to a higher impulse on both parts. Basically a heavier BCG should have higher momentum at the beginning of the rearward stroke. Whether or not it will still have higher momentum when it bottoms out will depend on the time it spends under the force of the recoil & hammer spring (compared to the time a lighter BCG would spend). To eliminate time as a variable, I used energy calculations since they're independent of time. And while as you said, energy calculations cannot be used to describe what is the force applied to the rigid frame of the gun while the BCG gets from the front to the rear of the receiver and vice versa, they should be valid to get us to the end points, by allowing us to derive the velocity at the end point in terms of mass, and sub that into the momentum equation. Ultimately, that was what I did.
I think the difference on recoil is even more pronounced with handguns. Shooting a P320 full size slide along with a P320 X-Five slide with its factory lightening cuts, all on the same frame, the difference is really evident. It's a lot easier to track the sights through recoil on the X-Five.
But that pistol really didn't like it when I tried adding a compensator. The regular full size just took it and ran...
Excellent video. I enjoyed every second.
Physics student here, 5:12 . Sometimes when you need to calculate the integral of a changing/dynamic force. It could be way easier to use conservation of energy formulas ( as they don't depend on time)
I'd love if you could do a friction comparison of the different options, perhaps by comparing clean vs dirty bolt velocities with standard milspec, lightweight, and possibly different coating types. I think that'd play a bigger role, perhaps pushing users towards a heavier buffer and cutdown BCG for better reliability than milspec. Or if the friction really doesn't matter, in which case the cheaper lighter buffer and milspec BCG are better.
I recall competition shooters complain about occasionally outrunning the bolt on semi-auto, pressing the trigger too early and having the hammer ride on the back of the bolt causing a light strike.
You are lowering rate of fire with lightweight bolt if you balance the gas system.
Another issue is using 556 as part of NATO alliance: the 556 has a range of pressures allowable as well as bullet masses. Your rifle has to run with excess bolt energy most of the time to use them all reasonably well and Ukraine has shown that some rifles are picky about the country of origin of their 556.
Great Video!
Neat, I often was curious of these things.
You weren’t kidding on the nerd warning! 😂. Great video tho
10:38 Reminds me of when I tried to pull start my snowmobile engine without the clutch (basically the engine’s flywheel/part of the CVT belt drive, the clutch easily doubles the engines rotating mass). It was impossible to overcome the compression stroke without the additional mass of the clutch helping overcome the compression stroke with inertia.
This is an interesting way to make AK rifles(especially 7.62) lighter shooting but to make it truly function requires tuning the size of the gas port, the strength of the spring, and various other things.
You're missing the foward force that happens when the BCG is launched backwards. Which somwhat cancles out the recoil from lauching the bullet
A heavy BCG can be very smooth shooting if it can decelerate with long traveling distance. Like that of the Ultimax 100. But most rifles don't have very long receivers to accommodate this.
So with a nomral length of travel, a lighter BCG would have less momentum when it hits the end of the receiver
Yup. The recoil behavior of a gas operated gun involves the rearward impulse from the bullet when the bolt is still locked, the forward impulse on the front wall of the gas system, the rearward impulse transferred through the recoil spring when the bcg moves back, the rearward impulse of the bcg striking the back of the receiver, the rearward impulse transferred through the recoil spring when the bcg is pushed forward, and the forward impulse of the bcg striking the front of the receiver. But I was not ready to do all that math at once and compare them as a function of reciprocating mass, so I just swept most of them under the rug lol
The recoil impulse is the same.. When used in a constant recoil system, it spreads the force over a longer period of time instead of all of a sudden when it impacts the rear..Constant recoil was first seen by Sullivan and Stoner in the German STG44 (MP44)..@@cabbage6015
What many people don't understand is a heavier buffer's effect on dwell time (bolt unlocking) is insignificant..This was proven years ago by Colt and recently by SilencerCo' testing with a high speed camera and computer..A heavier buffer does have an effect on carrier velocity..The extractor will lift completely off the case rim (after) the bolt un-locks..It is the residual pressure that holds the case against the bolt face that allows the extractor to lower back down to perform the extraction process.. The hotter the chamber becomes the hotter the brass case becomes and the longer it will take for the case to relax (objuration) to occur..This is why carrier velocity is so important to reliability..A heavier or lighter recoil spring can have the same effect as increase in the operating mass..
I think it's nonsense what you're saying about dwell time because I've never heard anyone talk about BCG mass as a primary factor in dwell time. Some people might have a wrong idea what dwell time is but that's not the point.
Interesting. I think I read somewhere (probably Sturgeon's House) that the residual chamber pressure after the bolt unlocks contributes a fair bit to the bcg's kinetic energy going rearward, and also makes the extractor lift up like you said? I wonder if this behaviour is unique to AR-15/AR-10 pattern rifles where there is little to no dwell time built into the geometry of the bolt carrier's cam track, as opposed to AK pattern guns where there's like 10mm of bolt carrier travel before the bolt starts to unlock?
I was talking about buffer weights, not carrier weight..@@ipanzerschrecku4732
The dwell time is from when the bullet passes the barrel gas port to the time it leaves the barrel..It is the straight part of the cam track that effects the residual pressure..LMT increased the straight part of the cam track to allow more time for case (objuration) and it work perfectly in the M4 platform..The reason the military did not adopt it was because it would not work reliably with the rifle length gas systems and it would have required supply to carry two different types of carriers..The extractor lift study can be found at AR15 repository..The test was done by the military TATCOM (Understanding extraction lift in the M16 family of weapons)...@@cabbage6015
@@hairydogstail I think in your first comment you mix up dwell time with lock time. But explain dwell time well in the reply.
I've found through my own amateur experimentation that buffer mass does effect lock time, it's only logical that it does. However what's actually key is the ratio between the mass of the carrier and the mass of the buffer. The higher the buffer mass in relation carrier mass the more effect it will have. The reason for this is that even on a standard cam track there's still a time when the carrier is moving back without rotating the bolt. The movement of the buffer mass slows that initial movement.
I wonder if this has anything to do with the ratio between the mass of the bolt itself vs the mass of the carrier. Because altering bolt carrier mass while not altering the bolt mass will result in reduced rearward kinetic energy after the bolt is picked up after the unlock process. Iirc the fw army ordnance manual talks about a ratio of 3:1 for ideal carrier to bolt mass ratio. So there might be something there ig. Lighter carriers also require stiffer springs as seen in the foxtrot mike bufferless carrier uppers, which makes charging more difficult. Maybe a reason they went with the forward charging mechanism. Just a few thoughts ig.
The only issue I had with the enigma was taking it off.
My work around to leaving a gun in my vehicle was to carry another holster.
I carry a custom IWB holster and move my pistol to that if I need to leave it in my vehicle.
If I need to take off the enigma in public, I don’t need to worry since I placed it in another holster.
My leg strap has never disconnected on me. It’s defiantly operator error.
Love this .... Can we get more
Great video
now can you do a video on a light BCG running a UNRIVALED TECHNOLOGIES DEAD BLOW BUFFER SYSTEM ?
Never forget, if an informative video seems too long or boring, turn on captions and put the playback speed at 2x, you consume more video in less time :D
I would like to learn more about the bolt carrier mass to bolt mass ratio.
Make more of this, please
more of this, please
This may be a tedious or insufficient request but could you possibly make your following videos louder by chance? I'm a little hard of hearing but love the content. Also larger letters would he an absolute delight as well. If it's too much then ignore me entirely, my feelings won't be hurt but I will cry in the shower after that
One other major factor with mdr issues you hear of is caused when used with 25 round pmags in 308 there is an early release and uncontrolled feed when coming from the right feed position on all the variants of that mag from full cap down to 10 rounds once it’s down to 10 remaining the feed from the right position works perfectly the left feed position has no issues at all for the entire mag
I think an explanation for why the energy is the same in the two configurations is warranted: The lighter Bolt Carrier System has the same force(F) from the gas cylinder(because piston cross sectional area and gas pressure are the same), but its lighter weight make it accelerate(a) twice as fast, but since the stroke distance(s) is the same the force from the piston is therefore acting for a shorter period of time, hence the final speed is not twice, and energy is therefore the same. (a=F/m), (2*a*s=v^2)
Aaaaand you just earned my subscribe. Kudos.
Phenomenal video.
great video dude. more of this!
Peter Kokalis used to make a big deal about the Bolt carrier to Bolt mass ratio. I presume he'd read the US Army Weapons Command’s 1968 “Technical Notes: Small Arms Weapons Design” and gleaned that from it.
Peter Kokalis was the go to guy back in the day..Many of his discoveries were lost with modern firearm writers such as the AKM's 5 piece (so called rate reducer)..It is not a rate reducer but an anti-bounce device..
@@hairydogstail I always enjoyed his writing. It really sparked my interest in small arms technology. That bolt to bolt carrier weight ratio seems to have been forgotten or cast by the wayside too.
Ah, the age old problem of competition guns being too overspecialized
idk why but that forward* edit cracks me up as hell
Right near the start I question the assumption of equal kinetic energy imparted; I would be curious to know how different the result may be if equal momentum is assumed.
Equal moment impulse may be the more accurate assumption, or at least something part way between fixing energy or fixing momentum. This is because the initial gas charge is based only on barrel pressure and time from the bullet passing the port to exiting the barrel, and that kinetic energy transfer comes from force and distance while momentum comes from force and time. The restriction of the gas tube is likely substantial in the analysis, and the time of bullet in the fast end of the barrel (port to muzzle) is likely much less then the one directional travel time of even the lightest bolt carrier.
This of course depends on the dynamics of the initiating gas pulse, specifically how it dissipates both the static and dynamic gas pressure from a shot.(and assuming semi-auto so the time between cycles prevents direct pressure wave interactions. (Residual heat in the parts effecting conductivity and part clearances would be the only interaction of one shot on the next).
As far I know no common designs use a checkvalve so there would be more loss of pressure back out of the gas port with a heavy slower mass. How much backflow likely involves timing of pressure waves not unlike tuned header pipes or expansion chambers(2 stroke) on a piston engine. If backflow loss is substantial then equal momentum is almost certainly a better assumtion than equal kinetic energy.
I have not calculated the relative cooling effect on the gas charge due to expansion vs conduction to the gas tube, piston, and cylinder. If conductive cooling is proportionally significant than the slower heavy bolt will also have more pressure loss from a given amount of hot gas and again tilts toward equal momentum.
And yes I read the pinned comment.
12:53 The WLVRN is definitely a promising design, but that inconsistent ejection pattern (provided the ammunition was quality controlled) looks like a bit of an issue. There are so many possible causes that saying anything is most definitely being an armchair-gunsmith, but seeing as they had issues with it on the MDR, I'd be interested to see if they properly upgraded the ejector spring to compensate for the change in BCG momentum when going with the heavier BCG; at least when a loaded magazine is exerting a force upward on the BCG (as the first rounds eject forward, and progress rearwards as the magazine nears empty). Definitely looked like something was going on there.
I see this "debate" go on in forums, whenever it comes to "tuning" their rifles. I will admit, i enjoy tuning and optimizing myself but i always try to prioritize reliability first and foremost. What are your opinions on messing with spring strength meanwhile then? We often see lots of mentioning regarding the BCG and buffer masses as they are the reciprocating bits of the AR, but there really has been an increasing proportion of folks going into stronger springs to take the role of or compliment these buffer weights now. I am seeing some folks preferring to make up for the lack of a buffer weight with a stronger spring instead (so instead of perhaps a carbine spring with an H3 buffer, i would see them using a 15% XP "blue" spring or even a 25% XP "red" spring with an H2 buffer or lighter now rather). Assuming a full mass BCG still of course.
I haven’t thought about that too much but it seems like a good idea since you’re not reducing the energy provided to the bcg by the gas system. A stiffer spring will absorb more kinetic energy during the rearward stroke, so the bcg will bottom out with less force, but the flip side is that it will give more kinetic energy to the forward stroke so the bcg will hit the barrel extension harder. But I guess a heavier buffer would do that as well, and it doesn’t have the added reliability benefit of a stiffer spring. Another thing is that the extra kinetic energy forward may or may not lead to more bolt carrier bounce, but that’s probably a non-issue in semi auto
Spring will not make up for buffer mass, they have a different roll.
I can see a place for a heavier spring with full mass systems, but not with low mass systems.
In this example from the original commenter, velocity of the bolt carrier will increase (your thoughts on forces can be equalized if the reduction in mass and increase in velocity end up at the same force). The only concern I see if this approach is taken to far is the magazine may not be able to present a new round in time or the extractor may not new strong enough to not “bounce” at the wrong frequency and slip off the case head.
Feel free...to do a lot more of these. Geek the F... OUT! Cool video!
The only way that you can possibly help the light carrier problem’s (that is failure to feed or failure to chamber rounds all the way) is to add a *bigger* buffer weight and with longer weight travel (meaning a longer buffer). But that would only bring you back to square one by adding more weight again.
I wish I was smart enough to really understand all this but loved the video.
What doesn't make sense to me then is that you will generally notice a fairly obvious decrease in felt recoil when using a HEAVIER buffer. You can try it for yourself. Take any off-the-shelf AR-15, they will normally be over-gassed with a standard carbine buffer (~3 oz) to ensure reliability in cycling all types of ammunition. Swap the buffer for an H1 (~3.8 oz) or H2 (~4.6 oz) buffer, and you will normally see a noticeable decrease in felt recoil. The weight of the buffer will be the only factor that has changed.
Why is that? It seems contradictory to what you explained here. Not trying to say you are wrong or anything, just curious and would like to understand more.
If you ever want to discuss roller lock G3 let me know, I can help. I am a retired armorer and nerd for them.
And what top 3 facts about them which the broad masses of the people don't know?
And do delayed blowback (lever or roller) systems have future and benefits over piston operated and short recoil systems?
Can you make a video on the A5 buffer system? I always go with A5 just because people say it's better than carbine, but I really don't understand why a rifle spring is better.
I very much suspect that the standards of springs and cartridge rims in ars were made without the assumption that bolt carriers will get this much lighter and that is likely the cause of the mentioned issues.
This is all why just using a stronger spring is the way to go
Well, not exactly. Springs need to be tuned-just like gas or a BCG.
Too strong a spring, you’ll either fail to extract or your BCG will slam into the front of your gun. Too weak a spring, and you’ll run into the same issues the video mentioned-bolt slamming into the buffer tube, stripped extractor, etc.
Ig in the context of making a reliable AR15, a strong spring is good. Competition shooters tend to lighten their springs.
@@noahchong9130 yeah obviously I don’t endorse just throwing the strongest spring in there right off the bay. But tuning it with whatever is the right strength. Just like how we don’t go straight to h4 buffers
Damm, i really wish i paid attention in math class.
6:26 Im pretty sure the force should be the same in both. You said it yourself, the cylce rate is faster with a lighter bcg and so immediately its obvious that time cannot be the same for both in the momentum eqn . I think the fact the Bcg is traveling back and snapping back forward again is what is causing the “lighter recoil” feeling. “Recoil” isnt just the first half of momentum, its the equal and opposite forward momentum as well