Ask Ian: Why Don't More Rifles Have Captive Pins?
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- Опубліковано 9 лип 2024
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Edit: I mixed up the selector and rear pin holes; the rear takedown pin hole is not stepped. Sorry!
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From Ryan on Patreon:
"Why do more rifles not have captive takedown pins? It seems that if someone is developing a rifle from the ground up there are almost no drawbacks to having them, especially if the rifle is going to be widely fielded. Is there a hidden cost?"
Having captive pins does add a few more small parts, machining operations, and assembly complexity to a rifle design. However, more important is that not all materials are conducive to captive pins. There needs to be a way to house the spring and detent pin necessary to create a captive takedown pin, and materials like stamped sheet metal and polymer are not usually well suited to that. Stamped steel has no space, and drilling the necessary holes in this polymer walls creates weak points.
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"How typically Swiss is it to manufacture a pin that is capable of malfunctioning" 🤣
I'm heading in to work this morning to address some Swiss metrology equipment that is overly complicated and is always breaking down.
Sounds like the user is failing the equipment, not the other way around 🇨🇭
@@MenwithHill Yeah, idk where the Thinking comes that the "German" (i mean all "Germans" so CH,AT and DE) Things are "overengineerd" and "complex".
The Machines and differnt Things i have from the "German" Countries are all reliable and i dont have Problems with them or my Neighbors.
Firms here use Mercedes, Man Trucks; Porsche, VW, Mercedes, BMW, Audi Cars; Stihl Chainsaws or all the German Wood Processing Machines we used were all from these 3 Countries.
I never heard that they are overly complex or fail more often. If this was the Case the biggest Construction Firms would not exclusivly use Liebherr Excavators or Wheelloaders...
Maybe the other Stuff is just too simplistic...
One question must always be: is it more complex than what it needs to be?
And the next question: Given a fresh start, can it be simpler and perhaps even do the job better?
The second bite tends to provide a better solution especially if the first one can be played out to functioning (or dysfunctioning) prototype.
Keep in mind that the ultimate simplication is elimination. Step back and given a better understanding of the whole from experience with the physical artefact, can you eliminate the need by modifications to another aspect?
Adding to the turmoil in the Engineer's mind is the pressure to make something that will sell. Soon, and with profit to justify further development.
It is easy to meet specified requirements. Ask any Elbonian.
@@MenwithHill Haha. Nope. Too many unnecessary bells and whistles that add points of failure and no value (for our application)
Well in this case, it may be typically Swiss, but it's not uniquely Swiss. Those kind of pins, with a built-in spring detent that's released by a push-button at the end, are common in the aircraft industry. I saw them all the time in my old job (aircraft factory parts supply). I'm not aware of any particular problem with them, and it's not like they have more parts than any other solution: it's just a matter of whether the spring and ball are in the pin or in the gun/airframe.
I clicked on this thinking “how much could there be to it” but clicked all the same knowing Ian would blow my mind. As always, he did not disappoint. Thank you as always!
I've never fired a gun and am not particularly interested in guns, but for some reason I watch *most* of these videos because the engineering and explanation is really interesting to me.
100% this!
Exactly what I was going to say, Ian is beyond a doubt the definition of an expert.
I am an electromechanical engineer and this explanation is simply spectacular. A huge envy to Ian who can show so many examples with their own weapons. I also think I should send a shout out to Ryan (who asked the question) because it's one of those aspects that we don't usually consider but are very important when designing. Greetings from Patagonia Argentina
As often the case the smallest of details making the largest impacts, certainly makes you appreciate how much thinking has to go into even something like this
Fun fact, Ian actually happens to have an associate's degree in mechanical engineering technology, likely part of why he explains everything so well
As an Austrian I have to disagree (slightly) on the pin on the AUG not being captive.
In standard military use the pin is actually captive, as it contains the rear sling mount and you can not really remove the front sling mount. So the pin is not captive in body of the gun, but it is connected to the sling.
Good to know. Thanks.
that's very cool. thanks you
Mechanical Design Engineer here - in my experience most initial designs have all sorts of features to improve the quality of life for both Production staff and end users, most of which get cut once management decide they need to meet some ridiculous profit margin..
Yeah, that checks out.
I think the bean counters might not call budget constraints ridiculous. We all have to answer to someone.
@@HD-J.R. to some extent sure, but having worked on projects where major considerations for assembly teams have been canned to make 80% margin instead of 75%, I can assure you there is definitely rampant profiteering to be found
@@Ben-rq5re I'd say to a larger extent than most realize. Being on the supply side to military procurement, and managing manufacturing production for 25 years, manufacturers/suppliers do not make the money people think. Politicians, regulators and Wallstreet make the lion share these days.
Your argument has more validity in consumer goods, but not in firearms or average military goods. I cannot speak to things like planes, tanks and missiles... etc...
@@HD-J.R. Unfortunately I’m not in military supply, I design inspection robotics for the petrochemical industry - there’s truly ludicrous amounts of money floating around, and every company is trying to grab as much of it as they can. Just to be clear, I have no problem with making profit, just when it comes at the expense of either end users or the people responsible for making the products bringing that cash in.
The AR15/M16 rear take down pin detent hole is 0.094" and is not stepped
as you said. I think you are confusing the selector detent hole which
is internally stepped.
Yup, hence my note in the description text
Why is the selector detent stepped. Does it serve a purpose?
@@RiceCrisp320 Speculation: if it were a single diameter detent it can fall out due to the hole size for the selector shaft axle. Since the selector is sometimes removed as part of removing the trigger group I guess they decided to make sure it was captive. This also makes assembly slightly easier in that it can not come out of the detent hole before the selector is installed.
This is a question I’ve wondered about for ages.
Makes sense that it isn’t always viable. I think the H&K solution is the ideal middle ground if you can’t have captured pins.
At least provide somewhere on the rifle to keep them secure and safe. Because if you drop a pin in tall grass it’s just gone.
It’s honestly just such a different set of design criteria for a service rifle vs a commercial rifle, you have to grunt proof everything.
It's a question I've always had too.
Decisions like this often come down to what government procurement people want rather than the manufacturer or, in civilian rifles, what the marketing department says will sell best.
Place to store and a couple extra pins.
@@InfiniteDarkMass Like having two pins at the back fo the G3, when it really only needs one....
Why? Extra pin, right there.
When a solder loses a pin, the captive pin is worth the trouble..Great video with perfect examples of the pro's and cons of captive pins..
captive pins are a travesty against muh freedum
That's what NCOs are for. You LOST YOUR PIN! You HORRIBLE LITTLE MAN!
@@chinesesparrows What would a Chinese subject know about freedom??
@@hairydogstail not much cause they brainwashed since birth
Agreed!
I love this new Q&A format!
It's indeed nice. The bite-sized single question videos are much easier to watch, no need for a whole movie night :D
I also probably is much less intensive for Ian to make than his usual globe trotting. I hope it stays as a once/twice a week deal.
Me too!
Me to. For someone like me whos not super knowledgeable but very interested I dont feel overwhelmed with info
Kinda miss the fancy clothing and booze du jour but I agree.
One trick for guns that do not have captive pins: Get a full replacement set and attach it to or find a way to install them into a cavity in the stock. If you have replacement parts on hand you will never need them. If you want a belt and suspenders approach, get two sets, one for the stock like I mentioned before and one for your cleaning kit.
Yep. "2 is 1 and 1 is none" as the old adage says.
We hope that more companies copy Heckler & Koch's habit of installing dummy holes for pins when the gun is dismantled.
Soldiers will be soldiers, you could be taking apart rifles in a group and those pins WILL get lost somehow. Sometimes 3 is 1 lol
@@robertwarner5963 You always have "dummy holes". You can always stick the pins back in the original holes on one or the other components after separating them.
Alternatively, get a gun that doesn't have pins you can lose :)
In my experience the AR rear detent hole is a single diameter. The detent pin will happily come out of the hole into the take down hole. The pin itself keeps the assembly together.
Every AR lower, ever. 😉
@@a.k47-74 sending detents across the room when building my first AR. Ah, memories. I’m so lucky I found them. I put the lower in a big plastic Tupperware tub and assembled the takedown pins in that, so it didn’t happen again.
Yeah I was like "wtf?" when he said that and went and checked one, definitely single diameter, detent is simply long enough to stick out into pin without coming out.
Yes. He's not as perfect as some seem to think.
Ian really deserves a lot of subs because he answers the question really well plus he explains them through giving us demonstration and setting up examples.
He gets paid for it.
@@MazeMaker4Life Politicians get paid for "doing" their jobs. Doesn't change one is deserving of compensation and the other is deserving of tar and feathers.
If the world were a place where people succeed solely on merit. Ian would have the biggest channel on UA-cam.
@@MazeMaker4Life sure, but Ian deserves money for his content more than a lot of people making way more money on youtube
The AR15 style takedown pin is just way too complicated. The Swedish AK5 (FN FNC) has a captive takedown pin similar to the VHS-2. The pin is a single diameter with a ramped smaller diameter near each end. Around the pin and inside a milled slot in the receiver wall is a horseshoe shaped bent wire clamping around the pin, thus locking the pin in either the in or out position by springing into either smaller diameter end-groove.
Being a mechanical engineer, this seems like a way cheaper and easier to manufacture solution than drilling tiny holes for coil springs and detent balls and milling keyways in the side of the pins. Also, both takedown pins are identical using this solution. You should take a look at it if you have a chance, Ian.
This brings me back to my high school engineering class I took. There are many factors involved even when wanting to use captive pins on a weapon. Materials, Cost, layout, and complexity all play factors into it.
Your High school class taught engineering for weapons design? Have a hard time believing that. Even covering weapons in the class is hard to believe. Even start of 2000’s it was a quiet don’t speak of it type of thing.
@@1014p it was a general engineering class, not for weapon design. The point I was making is that the types of constraints are the same in regards to engineering the parts that were covered, which were captive pins.
In an AR, the wall thickness is wider than it needs to be to allow for the hole for the spring and detent. It could be thinner and lighter if it didn't have a captive pin.
Same for the fire selector detent.
And the wall thickness to achieve that same strength with a detent pin channel with most polymers would make the receiver (at least in those areas) a *very* Chonky Boi indeed. 😁
A moment of silence for all the dropped pins out there.
Lost, lonely, replaced and forgotten.
Replaced but not forgotten!
Just like my ex wif-
I'll save my sympathy for the dropped and lost gold coins and gold jewelry
So as a swiss I've only seen two material failures on the SIG 550.
The rubber parts, the stock rubber part and the charging handle.
I know people that haven't cleaned their rifles in years and never heard of captive pins that stuck.
The real question, isn't the performance in Switzerland climate. It's what happens if those rifles got put into a swampy bayou situation? Would the pins that haven't had any issues in a more moderate mountain climate, behave the same in Vietnam, Laos, Congo, or Louisiana? I can't begin to answer that question. But, it has happened with rifle designs in the past multiple times.
@@SlavicCelery Don't know, luckily for us swiss we probably won't invade in the near future a sub tropical country.
But I get where you come from, I would argue that moist climate had more effect on rifle with wooden furniture (expending wood stock by absorbtion of moister). Polymeres and metals might not be that much affected by that.
Again I know people that, putting it lightly, haven't given their rifle much attention and I've never seen those captive pins with rust.
You could not turn the gas regulator not even mentioning taking of, the outside of the barrel full of rust, and the chamber full of brass particles and sooth.
But the captive pins worked, the gun worked.
And I forgot a common failure of the gun, that little black plastic that kerp the stock folded that also likes to break sometimes.
Not a common thing but it happens. So sometimes you see guys with a hanging stock.
But again besides these 3 things the gun is from my perspective almost impossible to break. Without bad intention ofmcourse.
@Forgotten Weapons
3:58 A reminder from a retired Austrian Army NCO who used AUGs for over a decade (and still does in the army reserve): *_Never_* pull that rear pin out right away on a Steyr AUG.
Instead, do it like you did it in your video about the AUG where you did it the right way: push in the indentation on the buttplate, *_push_* the pin *_in_* all the way, remove the buttplate, push the "button" thingy on the rear of the fire control group, *_and then_* pull the pin out.
There are two reasons why you should always do it this way:
1) Disassembly is a lot easier and smoother that way, because the two C-shaped thingies on the buttplate aren't in the way when you pull out the pin, so it's much less fumbly to get the pin out;
And second (which is more important): if you pull the pin out right away like you did here, the pin as well as the two C-shaped thingies on the buttplate can get worn out over time which - as you might imagine - ain't good.
I've experienced two _really_ old AUGs during my stint in the Austrian Army where the buttplates didn't have a snug fit on the stock anymore because they were disassembled in that wrong way too often by careless handlers and thus needed new buttplates because the C-shaped thingies were just worn out too much.
And while this might sound like me splitting hairs, it's actually just a) good form, and b) following the wise tried and tested principle of: "always take good care of your weapon, because then your weapon will take good care of you when you need it".
Apart from that: still a great video, of course!
I love it when Ian nerds out on technical details.
My favorite part was when he said "it's nerding time!" and nerded all over those guns.
I like what HK did on say, the G36 (or so I think, I don't have access to firearms in general): They have little holes in the stock to park pins in while you take the rest apart. Seems like a good idea for not losing pins in the field without making them captive.
HK did that on their roller locked guns with fixed stocks, like the G3, G33, G41, and MP5.
A tiny remark on 8:20 - right above the hole I can see the circular witness mark from manufacturing, hinting that the hole might have been molded in - which would be somewhat superior to machining it.
That pin mark would be there either way, as you can see on the other side of the part. Not much of a hint to anything. It's still a weak point that will fail.
You're correct, that hole would be formed by a pin in the mould, not drilled. I'm pretty sure Ian knows that, but wanted to simplify the explanation.
From what we can see in that shot, it appears that the hole is in the same direction which the mould opens, therefore the pin would be fixed to the mould and relatively low cost to implement.
The witness mark above it is from an ejector pin, which would be necessary regardless of whether the pin hole was there or not. You can see the ejector pin mark on the other side of the receiver as well.
That witness mark is not indicative that the hole next to it was molded in.
Instead, what that witness mark indicates is that there was an ejection pin that impacted that point on the part (and many other types of witness mark on injection molded polymer parts will indicate either that or a point where material was injected into the mold, as well as perhaps one or two unique witness marks that serve identification purposes such as what material it is made of or when it was made, however those are usually self-evident as such at least on consumer products, unsure if the same is true with polymer parts for firearms).
@@44R0Ndin it indicates the ejection way, which is in line with the holle, thus it might be easy to implement without extra costs and eliminate a drilling procedure.
@@trischas.2809 yup, that's a mold gate.
Some German Army instructors teach an advantage that non-captive pins have: you can install the pins from your non-shooting-hand-side, so while your rifle is slung and rides along your body, there is no way the pins get pushed out of position by equipment etc.
Were the pins coming out because they were inserted from the non body side a real problem?
@@otm646 my guess is: absolutely no. I've been in the service for 10 years, and vastly used MP5's, never had or seen a man push one of those pins accidentally neither by their gear or by the environment... There's one way to take them out, and that's voluntarily
I was in the Army during the time of ACUs and excessive velcro patches. In theory, us privates weren't supposed to disassemble the bolt of our M16s while out in the field because the firing pin retaining pin and extractor retaining pin are so small and easy to lose. I went ahead and disassembled everything anyways, but put those pins underneath my rank patch. Say what you will about the many many many flaws of that uniform, but it was nice to have a place to stash small gun parts.
Ian I just want to comment that I love this new Q&A format. I never really had a good reason for not watching the hour+ long Q&As, but these closely match your standard video format and I think that is what's working here.
^^ THIS ^^
Yup. It's easier to pick & choose which question I'm interested in, rather than watching one long video with 6 different questions.
As Ian gives an interesting presentation of just about any random question dropped, I actually prefer the hour-long Q&A, as I each and everytime learn things I didn't know beforehand I'd find interesting, much less be actually useful in other areas.
i mean that swiss style of takedown pn has been used since the 60's so if it had problems they proberbly already fixed them
I've spent some time with SIG 550s, there are issues, but the pins malfunctioning, while it may happen, is not something that I remember happening to any of my soldiers or fellow NCOs.
That was a great breakdown, makes you think more about the engineering than just a feature list. Good stuff Ian.
We sometimes forget that a gun is really a machine and how complex it actually is.
Surprised you overlooked the captive wedge on the AUG that holds the receiver and the stock.
Though it's not a pin as such, despite functioning as one.
Immediately thought of the AUG as the epitome of design built for field conditions.
Maybe it's just because of how hard it would be to get a good camera angle on the little sheet metal spring assembly that holds it in place. The AUG, though, is such a good example of the designers going the extra mile only for parts that are most likely to need disassembly in the field, I'm also a bit surprised he didn't at least mention it. The butt pad pin is already sort of captive simply by virtue of being attached to the sling swivel. You're not likely to lose it in the field unless you misplace the whole receiver. The AUG has advantages and disadvantages, but it's definitely one of the most elegantly laid out guns in history.
If your designing a rifle for a sport shooter to clean/dissemble at leisure captive pins aren’t essential. A combat rifle might need to be dismantled at haste and under pressure so captive pins make the process much smoother and reduce the risk of loosing parts.
When talking about the ar15 the captive pins were an ask from the us army if I remember correctly. Your own collection will show that the original ar10 was designed with non captive pins.
The Colt Model 1 (aka 601) utilizes a non-captive pivot pin.
@@x-calibearusallc I do think the title could be better. Any firearm that is purchased in a large order, the purchaser can demand anything they want. However magic is expensive and it all boils down to how much magic they want to pay for. On the other hand COTS are as is where is; unless they want to modify the COTS at which point it is no longer COTS and magic is expensive.
There are other ways to retain pins too. In some cases a part that is installed more or less permanently could have a feature which the pin would stop against. This can all be molded into a platic assembly easily enough. Havent seen it on any guns but have used something like it for a different project. A pin type part bad to not rotate so we had a macined flat. Assembling two parts together trapped that pin part in the bore from either being able to fall out or rotate. One part had the bores and the other part had a flat which just protruded past the bore and mated to the flat on the axle. There were some tolerance issues at first but it was easy to sort out.
I could see this on some guns such as having a little shelf on, say, a barrel trunnion or on a grip frame which is indexed perfectly to retain a cross pin. No tiny holes or extra parts to install, just a pin with a flat machined into it.
The FNC design is quite simple and should work on polymer receivers as well. The (captive) pins are round and can rotate freely. They have two grooves around the circumference, to hold them closed and open. The captive mechanism is just a fairly thin wire locking pin installed in a slot in the receiver from the top. They can be removed with just about any pair of pliers. If they get bad, remove them, bend them to get a tighter grip and reinstall. Simple. The pins seem to be turned on a lathe anyway and the receiver is milled. So there probably weren’t many extra steps in production.
I wrote a comment saying exactly this. This system is far superior in simplicity to the AR15 pins. Should be very cheap to produce.
an entire vid about captive pins from Ian is like an entire vid about track tensioning from the chieftain. absolutely mandatory watch material.
I've thought of this every time I'm crawling on the floor with a flashlight looking for a dropped shotgun trigger group pin.
Nice video, sir.
Captive pins have an anecdotal risk of damage to the receiver while disassembled by people who don't know the risk of leaving a captive pin extended. That is to say I've heard of (mostly new owners) disassembling, leaving the pin extended, dropping the receiver, and the receiver falling on the pin in such a way that it breaks the receiver (from pin on stoner designs). Rather than risk learning this the hard way many simply push the pin in while the receiver is disassembled. Similar to not leaving a hand drill with a bit in it when not being used.
I've seen more than a few M16a2 and M-4s having the front takedown pins broken do to that. I don't remember any of the M16a1's having it happen but I know it did on accident too. Arms rooms before "operation clean sweep" kept them in stock for replacement.
Ian, I've been watching your videos for YEARS. I always walk away having learned something brand new. I love these short Q&A videos. Keep up the brilliant work!
I’m really enjoying this new format for the Q&A. I hope Ian continues this going forward.
Very well said, Ian. In 2018 I worked for a company making injection molded parts and as a mechanical engineer this was my first time dealing with them. Me, being a very traditional engineer, made my prototypes with fasteners. The principal level industrial engineer instructed me that while my design was stout and reliable, every single extra BOM item I add makes the overall product more expensive. If I could use say snaps that worked with the required draft for the mold pull, most of this consumer device would snap together once and never come apart. Where more precision was needed for a linear stage we used ground stainless steel rods but again, if we could reduce part cost by integrating the bearing into a molded part instead of trying to press or glue in a separate bearing it would keep costs down.
While you obviously want the product, be it a consumer level device or even a firearm to be reliable above all else, if I can do that with 25% fewer parts it means that the client (even a military one) can get that many more firearms in the hands of soldiers. That was a side of engineering I was not exposed to, and you did an excellent job explaining it here. I also have to say for injection molded parts, thank God for CAD!
The example of a polymer part having its own small drilled section for the detent spring was fun to see. Makes sense they used a step rather than trying to use a boss, as the boss is usually no more than 50-60% of the wall thickness and you really, really want to avoid trying to have another part just for reinforcement. You can make it work for sure but it takes more engineering hours. But that being said, it would pay off instead of having a line down situation on lower receivers because that one metal reinforcing ring was running low in inventory. THAT costs way more plus the general added manufacturing time, rework etc that a lot of managers don't understand. Do it right the first time, because you'll easily spend 2x the time fixing it after the product has been released.
Something else to consider from the manufacturing cost side when making detents and captive pins: the tool to make the holes for the detent is almost always a custom tool. Machine tooling gets expensive fast and custom tooling like that even more so. Plus if you are a company that makes multiple parts on a single machine, getting the machine set back up and getting that detent operation correct takes some fiddling, assuming we're talking machined parts here.
If you're not doing captive, which as you've shown doesn't work with every material and design, I think the HK solution is probably the most soldier-proof because it has a defined order of steps. Yes, the take out and replace sort of thing Russell has pointed out with the KP15 works, especially since most folks will just remove one pin and shotgun the receiver open, I'm curious how many times it would take Private Schmuckatelli forcefully closing the upper on the pin accidentally to damage the pin, the rear pin hole, or the front pin hole. The average KP15 owner is probably a few rungs above guys who buy V6 Mustangs at criminal interest rates.
No, they are the same guys buying v6 mustangs.
I like this new "discrete question" format for the Q&As. I never watched the long, omnibus ones, but here I'm alerted to the existence of a specific question that interests me and I can easily watch just that part.
I am greatly enjoying this new Q&A format. By focusing on one question per video you provide such an in-depth and thoughtful answer. Loved the in-depth look at examples in this video to demonstrate your point.
I love the long session Q&A which are almost like a nice me time podcast.
I love this format even more. The fact that each question gets its own video makes it so much easier to reference.
@AUG: The rear takedown pin on an AUG might not be captive, but on a military rifle it is always fixed via sling to the receiver. And as such not prone to losing.
Exactly.
Also you can put the pin in from the other direction if you want to put the sling on the other side.
The Keltec RDB also has semi-captive pins although the furniture is mostly polymer. The pin hits a stop when you pull it out, but comes all the way out if you really YOINK on it.
I loved this and loved you showing us the different intricacies and work around solutions people made. Awesome
You should do more "disassembly table" Q&A. Not every question is suitable, but I really enjoyed the multiple comparison.
Ian, I really like this shorter Q&A format.
It's easier to pick & choose which question I'm interested in, rather than watching an hour long video with 6 different questions. Plus it's more bite-sized.
Really like this format for the Q&A Ian ! Great work as always. N
I think it is more appropriate to say that the difference between the kp15 and the aluminum receiver is due to the manufacturing process rather than just the pure material properties.
To add a retractable pin into the mold adds cost and complexity to the mold and the engineering involved. Whereas with the aluminum lower, if the blank in already positioned for machining of necessary features like the buffer tube thread then the cost of a small hole for a spring is tiny in comparison.
Take a look at the front take down pin spring bore on the kp15. Notice that there is no bulge for the spring? they've changed the geometry of the receiver and removed the home for the pin all together because they are trying to maintain a uniform wall thickness (within reason). If they added the bulge and decided to machine it after it is risky and costly. It could require them to machine in an orientation that they wouldn't otherwise need which adds cost. It could also result in a void in the center of the bulge and prevent you from having a nice straight smooth bore.
I wondered if this was also going to address captive recoil springs as well? They seem to have fewer downsides.
No manager wants to wait for the engineer to get this amazing captive pin finished before making profit.
Thanks Ian! Great format and appreciate the attention to detail you bring to us. Always fun and informative.
As someone who never watched the long QnAs, I’m enjoying these short QnA videos and learning in the process. Smart change Ian
I have to say, Ask Ian is one of the cool things you did on your channel recently, I love it.
I really like these question specific videos! It's much more easily accessible than the longer Q&A's (which are still awesome nonetheless).
There's another way to make the pin captive. And it's feasible both for sheet metal and polymer - axial profile cuts into the pin, similar to those on Steyr AUG rear pin, and a C-clip, traveling/tripping over them. Easy and cheap solution.
Just to add to this a reason why a lot of people don't just make the polymer thicker: to injection mold a part you want the part to have as constant a thickness as possible. If you add a huge bump out that is just filled with plastic then you will create a void or sink in the finished part because the plastic will shrink as it cools and could potentially create a weak point in the receiver.
Additionally, you really can't injection mold a part that is thicker than 0.180 or 0.160 without adding in things like foaming or gas injection which are expensive, and typically avoided.
Source: I'm a mechanical engineer that took classes specializing in polymer part design and production.
Great format for the Q&A's!
Superior video. I feel kind of stupid because I didn't think about putting the pin back into its hole (even though I often screw fasteners back in their holes as not to lose or get them mixed up when working on other things). I love when a video teaches me something especially when it's something practical.
Well done, i really enjoy these sort of cerebral deep dives, more of this please!
That's the first time I've seen a captive pin on the VHS. My military issued rifle didn't have that.
Not sure if that's an across the board product improvement or specifically done for the civilian market as I know the the guys in HS are well aware of the things americans love/fetishise over in terms of gun design.
Don't get me wrong it is super useful but honestly taking the pins out and putting them in a pocket really wouldn't ruin the ease of use here.
@@whatsmolly5741 i used to put the three pins into the went holes on the front handguard during disassembly and cleaning
I believe Ian mentioned something on his VHS2/Hellion video that the VHS(1) was used as a sounding board to get product improvement recommendations from field users that ended up in the VHS2/Hellion. I'll have to re-watch that video to see if I can find a time stamp.
I'd also add another note to this video. Tooling. Most companies will be either buying their pins from someone else or manufacturing in house a commonly used pin en mass for many guns.
Creating a relatively reliable, (no worse than a non-captive pin), self captive pin isn't that difficult. And the extra steps once your upto manufacturing sufficiently large numbers of them isn't a huge cost negetive either. But justifying the up front investment to do the new tooling setup is going to be hard without a serious need allready existing. And that largely isn't a thing ATM.
One method you missed for keeping pins captive was the sa80 solution of have a clip embedded in the steel body around the pin that stop it from being pulled out. Though these do come loose and need to be peened back into the slot.
That basically goes back to the Swiss solution of "design pins that can fail" option.
Albeit a failure that won't preclude *disassembling* the rifle... justva failure mode that might allow the rifle to fall apart in use (like M60 trigger groups falling off if the leaf spring is upside down).
Honestly, I’m surprised this question took so long to come up, given the always enthusiastic “this part is held together by this pin, which is captive which is always nice so you can’t lose it” uttered by Ian every time he comes across and shows us a captive pin. I was hesitant to ask this myself and sound like I was missing the point, or overthinking the pin. It’s a pin! I was satisfied with the “not all pins are captive, and not all pins are nice, but if a pin is captive it is always nice” proposition. I miss those simpler days.
I really like the format of these videos compared to the big Q&A. I know it takes more work, but I really appreciate it
What a great question and as well a brilliant and detailed answer. I am really enjoying these more short-form Q&A videos from you Ian! I hope that these also appeal to whose who don't have the time to watch your spectacular monthly wrap-ups.
Your knowledge and understanding of firearms is just amazing. Thank you, Ian!
As an ex military member, weapons do get stripped at night or in very low light occasionally. Captive pins are a much better solution. The Steyr AUG - the sling will ensure the pin doesn't go missing.
HK do not have captive pins so they can ignore you when you need one.
And after a LOT of efforts to get one, they can charge an arm and a leg to get a replacements.
The FN SCAR nailed it - just a little clip and a taper at the end of the pin. Just one extra part that’s incredibly cheap, and If it fails, no big deal, then it’s just a removable pin. The lower has a little pocket molded for it to hold it in place, but it is not load bearing, and still functions even if the pocket breaks. Such an elegant design :)
Such a simple question, but an amazing answer. Loving this style of video.
So glad you made this video I’ve wondered the myself for quite a long time
You do a nice job on these. I had several moments of "wait, but you can also do it like this..." and then you brought that up.
I've seen captive pins in non-firearms applications in which they used a C-clip that slid along the pin and was stopped by a groove on the end of the pin. While not fool-proof, it does require deliberate effort to pull the pin through the clip and seems like a good solution for sheet metal components.
One of the “features” of the SA80 was it used this method. If one did pull the pin all the way out it was almost impossible to get it back in without a tool.
Like the captive pins on the minimi. It's not that hard Mr. Stoner...
One of my favourite procrastinations is figuring out how would I design my own rifle. One of the things that I have been, "figuring out", are captive pins. Please feel free to make more of these types of videos :).
Especially on the manufacturing side of weapons production.
The SCAR has a captive pin on a polymer lower that is very sturdy and simple, a spring clip just pinches it in place, slotting into grooves machined in the the diameter of the pin.
I'm surprised that there could be so much to this topic, but I'm not surprised that Ian knew and could tell us all about it.
Hello Iain another way of implementing a captive pin is used on the SA80 L85 (yes boo hiss lol) series of rifles. This is done on the steel sheet stamping where a boss is welded on with a groove inside. This allows a very thin diameter wire "C" clip made of spring steel to be inserted and that interfaces with the grooves in the pin and the boss. It does work and while not as strong as say an AR15 style pin it is pretty cheap and can be replaced with a little bit of fiddling.
Thank you Ian, been wondering about this myself for a really long time and you explained the reasoning behind it perfectly^^
When CZ 805 came out people were asking "why it does not have captive pins?"
Than CZ engineers asked "why didn't we use captive pins?"
Therefore, CZ 806 had them
considering Bren2 was direct result of complaints from actual users... that simply means the soldiers WANTED teh pins to be captive ...
you know because a little extra cost on already overpriced rifle is worth not ending up with unusable rifle in middle of combat because you accidentally dropped the pin while clearing a malfunction...
I always enjoy your videos Ian. It's very interesting to learn how guns work, and the different options such as open bolt & closed bolt systems. I live in the UK where mostly we aren't allowed to play with guns as a hobby, so the opportunities to handle guns and learn about how they work is very limited.
This is outstanding stuff & so much better than hour long episodes. Excellent decision
Thanks for taking the time to show examples of captive pins. The VHS system seems to be the best idea for a polymer part because it spreads the stress across a larger area. Manufacturing the pin and retainer in-house may not be big deal for a large armes company. You should consider more videos like this that show how different gun makers solver the same problem!
A downside of captive pins is that if people strip the rifle and leave the pin sticking out it is very vulnerable to damage and training needs to be there for the pin to be "parked" back in its closed position, even with the rifle in kit form. Whilst this is a training issue it's still probably less likely for people to break the protuding captive pin than lose the detachable one. Then again, the finest belt fed machine gun, the FN MAG, (GPMG in British Service) has a TWO-PART(!) detachable pin securing the trigger group and everybody gets on just fine with that....
The rivets with thread in them is a industrial way to add threaded holes to sheet metal or other such material. "Blind rivet nuts/Blind nutserts" So the proprietary part is probably the pin/screw that threads into the blind rivet nut. It's still a impressive way to have captive pins.
I'd really like to see that rivet thing taken apart to show how it works inside.
Three cheers! A great look at what appears on the surface to be utterly simple, but when examined carefully turns out to be very nuanced and situational. The new Q&A format is really going to be a great improvement. Thanks for the wonderful content, Ian! (edited for typo)
Captive pins are useful. But if I were to try and keep engineering costs down when designing a gun, one thing I'd make sure to do would be to have one of the receivers have an indent of some kind with a magnet attached to the base and making sure that all the body pins and other small parts are made from magnetic metals.
So whenever you pull pins out and want to avoid losing them you just stick them on that indent and the magnet holds them in place until you need to put the pins and small parts back in their proper place again.
This would work until you face an enemy force armed with ultra-powerful electromagnets.
@@AshleyPomeroy I'm not following.
and what else gets stuck on the magnets?
you can also include metal parts in polymer injection molding (part gets placed in mould before plastic gets infected, can ve fully automatic process), for example a small diameter pipe for such a pin retainer. it does bring up the cost for the mould, of course, especially since you basically need three of them for every machine, but it's possible and wouldn't create a weak point like drilling into the part does. especially with an outside profile of the metal piece that'd help it remain in place and take over so evof the structure that's lost due to the void.
the bigger problem with the last one is the abrupt thickening of the polymer as that increases the chances of imperfections or voids in the finished part, while the sharp corners do create potential for stress while cooling and therefor inherent weaknesses if not dealt with properly (which does increase cost once again, as there need to be special accomodations made for this).
An answer to a question I wasn't expecting to hear. Very well done Ian
From a machining standpoint, most of the non-captive pins I saw in the video could be produced on just a lathe. Even with the side hole for the ball bearing or the slit on the end for the HK style pins. With the AR style pins, the track or slot down the length of the pin would require a whole second setup in a mill. Even if it's just a simple slot, it's still going to add time, cost, and (minor) complexity to the supply side that may make it a nonviable option.
Great analysis and commentary about design decisions.
was always fun when the captive pins on the Cadet GP L98A1 (manual operated SA80) came completely out. You couldn't get them back in and it would need a armorer to work on it. I imagine the same was true for all the early variations of the SA80 family
Yes, I've always thought when learning about a firearm, and the pins are not captive, why? Now I know. Thanks Ian.
I really like the short format single topic Q&A format
Ian, I will point out on your comments from the MDR...
Most plastics manufacturers will have those holes pre-planned in the mold. what they do is use insert pins while making the part to create these features instead of drilling holes. this eliminates the problem of having to weaken the polymer, but it adds more cost to your tools and dies for the part itself.
P.S. - A lot of people are going to disagree with me, but you'd think the engineers at Desert Tech were not stupid, and more than likely did just as I said; used tool inserts while molding the part to create these captive pin features instead of drilling holes post mold-shot. it's common practice among a lot of polymer part manufacturers.
P.S.S. - After some analysis of paused stills of the video, the tooling may have been simplified by using fixed extrusion pins machined into the mold tool, and although i can not see a parting line, the likely answer is that the die draw is going the direction of these features, which means that the mold opens and closes the same direction of these features, simplifying the tool and lowering the cost. At least that is what would have been done at the company i worked at as an engineer. Most of my work dealt in plastic parts manufacturing, as well as sheetmetal and welding assemblies. (Automotive supplier, in case people are wondering)
I've always wondered why you couldn't just have a spring clip on the pin. A couple of grooves in the clip, one in the closed position, one in the open position of the pin.
Neat content! I had never thought about captive pins before! Thanks!
A really seemingly simple compromise to me (I know very little about guns, basically just stuff from this channel) would be to drill little holes the same diameter as the pin holes and just deep enough to hold the pins securely with friction, right next to the pin holes, or somewhere on the body of the gun where there is space. Then, you could pull out the pin and put it in the little hole to stay during the process of disassembling the rest of the gun. It doesn't seem like it would be any less convenient to me than using a captive pin. The only problem I can think of is the hole would capture dirt/mud and be hard to clean, but I'm sure there's a simple workaround to that problem.
The Tavor and X95 uses a fairly simple solution. Instead of a detent, it uses torsion springs that can lay flat inside the polymer shell without having to compromise it's integrity or having a complicated installation. The spring itself applies pressure to grooves in the pins to retain them. It's likely how the VSH retention also functions.