Look up "Heat checking" very common in hardened tool steel. Used in casting. The surface can be heated to 1400°f in 1/1000 of a second the metal expands on the surface but just a few thousands deep. This sets up stress between the cooler metal and the hot metal. And bam stress cracks. The gasses cool some as they travel down the barrel so the is less the father you go. Plus the other things going on in the chamber also.
I agree 100%. I think the problem started when long range and bench rest shooters' messages were heard in a broader audience. They like to ditch a barrel that won't provide sub- 1/4" groups consistently. I also believe how one cleans a rifle makes a large impact. I scrub down my rifle and have been told well, you're making the bore larger, ummm ok, but I am still within SAMMI specs if I do. The bullet will expand to close those gaps due to the higher pressure. I also have a barrel that is well cleaned which doesn't look like it has 1100 rounds on it and it's a 6.5CM. The throat still looks new. You can't even see the alligator skin pattern until you're 4" past the throat. The carbon ring on the neck MUST be removed after every round of firing or you increase pressures by up to 4k psi. Lou Murdica has proven this in his testing. I just don't buy that a $1k barrel should be thrown away, because it has some erosion early in the bore. If that bullet is still capable of stabilization and not tumbling when it hits the target, then the barrel is still good in my opinion. If I have a 1:7.5 twist barrel and loose 6" of a 26" barrel to erosion, I still have enough barrel and twists to stabilize at least a 147gn bullet. In fact I'd argue that barrel can still stabilize any bullet requiring a 1:8 twist. Damn good info sir!
My cousin bought a 100+ years old 44-40 Marlin. It shot just over 1 MOA groups at 25yards. I wanted to test my new borescope and we were schocked by the amount of not only throat erosion but also previous rust marks on the rifling. The previous owner took great care of the rifle, but the couple of owners (some of them government/army) obviously didn’t. Regardless, the rifle defied all logic and still shot remarking well.
You are on the right track. The comparison you are looking for is a laser on the surface of steel. It is the pressure affecting he surface of the metal, and its is not the contraction creating the alligator fractures, it is the cool down. Imagine blasting the surface of the metal with a laser to extreme high temperatures, the molecules on the surface expand rapidly, the pressure is relieved in microseconds, suddenly cooling the surface. The material just behind the surface soaked the heat, but the material on the surface is cooling faster. So as the barrel is trying to go back to its original shape (from expansion) with the surface cooling faster, it creates micro fractures. The surface metal fatigue looses elasticity over time, and thus the cracks stay, and the barrel is worn out as metal elasticity has left the area.
Spot on all the way. one other thing is the expansion and contraction of the surface of the boor through heating and cooling actually hardens the surface and makes it brittle thus starting the cracking process.
@mikelong9638 and also lips cracks from drying out of cold. Outer skin lost elasticity. While inner flesh is still elastic. Outer skin trying to conform to moving elastic flesh cracks...
Excellent video. Thought provoking and probably right. I watched this as part of my search for answers to why my once very accurate rifle suddenly became very inaccurate. I suspect throat erosion and have a bore scope on the way to find out. I believe the exact cause of throat erosion is relevant. I might want to prolong barrel life, and if reducing pressure is the key to that, then that would inform me to reduce my handloads a bit...or a lot!
If the cost factor to make a barrel/load combo advantageous to the industry, then it shall be. Right now, we are living with it. Great, seamless presentation. Please keep it up! Mark Richardson
In response to your comment regarding "others smarter than myself", my sense is that tough there maybe others more educated, I doubt that there are many that are smarter. Great video.
It’s really refreshing to hear from somebody that thinks about something in depth and draws conclusions based on evidence, and is open to changing their opinions or theories. Imagine how much more advanced our society would be if more people took this approach as opposed to the more common approach: “This is what I believe, you cannot change my mind because I know I’m right. No I’m not going to test this myself and I’m going to ignore all evidence presented to me that says otherwise”.
additionally to your explanation I would add what is bullet inertia along spinning axel. it takes most stress on barrel rifling in first few inches to overcom bullet inertia and start bullet spinn . once bullet is in spinning motion riflings are subjected to less stress therefore less erosion further down in the barrel
the bore conditions kit that David Tubbs sells will polish the lake bed metal and rough tool marks in the throat and keep it running longer. I did a treatment on an M1a and it shot better groups. great video, make sense to me
I really appreciate the reasonable explanation of the cause of barrel damage. I agree, pressure would be, in my mind, the primary cause of pressure damage. The question in my mind is what can cause normal pressures to become barrel killers? I have three theories: 1. Poor barrel care caused by lack of keeping the barrel free from too much fouling, including powder residue and especially copper fouling. These obviously cause a degree of blockage in the barrel the bullet has to overcome when its fired. Thus, higher pressures. 2. Firing too heavy a bullet from smaller powder charges due to case capacity. I have a .308 Win in a model 99 Savage that I bought from a former client. From day one this rifle could't group anything less that a foot spread at 50 yards. I know the previous owner fired mostly 180 grain bullets from this rifle. I had a gunsmith clean copper fouling from the barrel. Still, no accuracy what-so-ever. I bought a bore scope and voila, I found the barrel is heat cracked most of the length of the barrel. In my opinion, due to lack of cleaning and using a bullet too heavy for the case capacity powder charge the barrel is history. 3. Poor quality of the steel used in the barrel. This is hard for anyone to judge. But, the model 99 Savage was a very expensive rifle to manufacture. My theory is, Savage started to take shortcuts in the manufacture to reduce their costs of manufacture. For this particular model year, not too long after, Savage discontinued this iconic weapon. I am currently trying to find someone to lathe a new barrel to fit the receiver or re-bore the barrel to either a .338 Federal or .358 Winchester. My thought is, with a larger bore and using no bullet heavier than 180 grs., plus my fussiness in keeping my barrels clean (very little brass brush as possible, if any) I should be able to get a very accurate rifle. I could retire the rifle but I don't want to have a useless weapon in my collection. I am open to the thoughts of others including Greg's.
2.3 Mechanical wear After the heat and the chemical effect, the base metal is prone to heat softening, mechanical strength and crack, etc. The friction generated during the coupling process is sufficient to consume the part of the matrix material. This is the main way of mechanical wear. In addition, due to unburned propellant particles and the high-speed movement of the peeling produced by ablation, the mechanical erosion of the bore is also great.
It is mostly heat. I used to repair light and heavy machineguns. It is nothing to see large chunks of lands missing from the breech end of the barrel. That is why many machinegun barrels have about an 8" stellite liner in them. Chrome lined barrels have less than .001 thick coating on a wall and pressure would crack that chrome quickly. I have seen old chrome lined barrels with tens of thousands of rounds through them and they look good yet.
Boat tail bullets make the problem worse, the base funnels gases ahead of the bullet making a very hot plasma torch prior to the bullet movement and the bullet then hits it.
Excellent discussion. I believe that you're partly right, in that pressure plays a role; but the cause also has to include the fire/heat from burning powder- or the firecracking wouldn't be most pronounced at the case mouth/leade, & progressively diminish towards the muzzle. I realize that society typically thinks in a "just get a new one" mindset.....but I'm much more interested in the "what can we do to restore it?" line of thinking.
An excellent hypothesis, you really are onto something and I have to agree with you! Stainless and chrome moly barrels, for example, are compressible and indeed some are made by cold forging. Heating them up will only increase the amount they will compress. I have noticed a similar effect to fire-cracking when hammering brittle steel. Never stop thinking and questioning the excepted norm!
Partially burned and burning powder granules impinge upon steel in a high pressure, high temperature environment sand blasts the lead of the barrel. The amount and type of powder makes the difference. Slow burning powder confined by the overbore is like a sandblasting torch. I shoot a 300 BO 100 yd target rifle with 1400 rds. thru it. barrel looks like new. Doesn't seem to be a problem with pistols.
Again, great video. We also must consider what's going on in front of the bullet. Tremendous pressure there as well. That bullet, and all the pressure behind it, is asking air in front of the bullet to get out of the way very rapidly, which it can't, which produces resistance or drag. Obviously the drag is overcome or bullets wouldn't leave barrels. But there's that bullet, in between two competing forces, vast amounts of pressure fore and aft. Something's gotta give...barrels, especially at the throat. Bullets, too. But I wonder about the malleability differences between softer jacketed lead and solid copper bullets which I now use and must use in California. One of my once very accurate rifles recently became inaccurate. I switched to nonleaded bullets 7 years ago in that rifle. And my handloads are pretty stout. Can anyone else corroborate this?
Got me thinking - a dangerous thing. If you are correct then a worn out barrel may only be worn out in the stressed area. Removal of the chamber and damaged fire cracked throat ( if the remaining steel were available - length/OD etc) and the barrel is then re chambered the barrel may well be sound again - within limits. If the barrel IS sound again then I pose two questions:- 1/ Is the barrel worn out because it is damaged? or 2/ Does the fire cracked throat impose damage on the projectile at firing.This may make the projectile not uniform or not stable in the barrel and/or in the air on exit and on its way to target? Some thing to keep us awake at night.
Hydrogen ( powder hi temp. decomposition byproduct)saturates the steel at Hi pressure and makes it brittle. The Hi temperature is another major factor. The way to mitigate the throat erosion is to use "cold" powders like a nitrocellulose powders with lowest nitroglycerin content possible or without it. + There are some different powder formulations with nitroguanidine compound. It's all traced back to the research about barrels in artillery pieces that was done after ww1. I can't remember exactly where I red about it.
Makes absolute sense, what is a primary test for all barrels? PSI. A prime focus of SAAMI criterion is to publish acceptable chamber pressure. A common theme of warnings of firearms producers is not to exceed the rated PSI. When PSI is a constant topic of concern across all aspects of the industry, it's as was stated in the video; "academic" to understanding why, how and what it is that causes barrels to fail, whether it's suddenly and catastrophically or over time...
I am not an engineer, but it makes rational sense to me that the most stress imposed on the metal is the explosion at the throat of a barrel, aka the chamber. Other than having an obstruction in the barrel, the only place you see guns exploding is at that location. If a powder charge exceeds the safe threshold of the firearm, this is not the weakest link, it is just the place where it is most likely to be realized and immediately.
There are many gunsmiths that agree with u. And if u consider the anecdotal evidence of high capacity or over bore cartridges accelerating barrel wear, in comparison to smaller cartridges.. it makes perfect sense as the whole point of the excess powder burning at a reduced speed is to prolong the pressure wave behind the bullet as it travels down the tube. One way or another, if u want performance it always comes at the price of longevity.
It is relevant if you want a barrel to last longer than it takes to find a load that works for it and if you want to innovate the field to make progression in shooting sports... Heat is also generated through vibration from the pressure and barrel harmonics... I have a custom rifle barrel that I had cut with a 4 inch shank with a diameter of 1.3 inches, rifled for a 7mm wildcat... I have shot over 350 rounds in the rifle and the lands have yet to move... The coal is around 3.6 inches and the lands are well within the 4 inches of shank... I also have a steep shoulder angle of 35 degrees that may contribute to throat life, but this barrel has outlasted the last one I had built by a long shot...
Interesting. I thought engineers where onto that because of the bulge you see in the barrel chamber area. If you have a way of measuring barrel expansion at detonation that would be an interesting info.
WOW... That is a trip.. I have never put any thought into the "How long does a barrel last?".. That answer blew my doors off, as I had always conceptualized that in "round count pending the caliber"... MIND BLOWING... Well, I know what I am gonna be talking about all day today, and the next month with the club... I hope you know, I am gonna claim your statement as my own, as if I thought of that clever way to say that..LOL... Just kidding...
I agree with you. I think a simple explanation is acseleration. When the bullet is launching, it moves the metal in the barrel, because its getting so much force. Its the same in dragracing. It rippels the surface, because of the violent aceseleration.
Ball powders cause less erosion than log powders, which are tumbling through the bore according to a couple of sources I've seen. Rates of fire are a factor as the hotter the barrel gets, the more susceptible it is to erosion. Cryogenic treated barrels are tougher, and there are also better steels. Speer reloading experiments showed calibers like 264 win mag was burning out barrels in unde 300 rounds. This applies to over bored short magnums. Pressure is definitely the main problem. This is also supported by Randy Selby, the gunsmith.
Sounds like the surface of the bore is work hardening while the subsurface is still ductile. The work hardened bore surface can't handle the bore expansion without checking.
2.1 Heat ablation Among the various factors that cause damage to the inner chamber, the heat effect is the primary and fundamental. The individual effects of the heat factor can lead to three kinds of failure phenomena: the thermal softening of the body surface; the thermal transformation of the bore wall; the melting of the surface. When the gun is fired, the volume of the material on the surface of the chamber is alternately expanded and contracted by rapid heating and cooling, and a sharp phase change occurs at the same time. The high temperature environment provides favorable conditions for the chemical reaction between the gunpowder gas and the metal in the borehole wall. The resulting white layer, such as Fe3C, will melt under heat and be removed by high-speed gunpowder gas to accelerate the inner chamber failure process. Melting ablation is the fastest and most severe ablation mechanism that causes the inner bore to be destroyed, which is particularly pronounced in high-bore large caliber artillery. Meanwhile, the heat can also cause the tube thermal stress, thermal bending and other undesirable phenomena, which affect the use of artillery performance on some degree. So the heat problem has aroused people's attention for a long time, and becomes a necessary factor in the design of artillery.
It's not often anymore you see people using their brain and commonsense at the same time. I've thought the same for many many years,probably since my mid/late teens when I then was reloading for a few years already. Like you say,the friction creates tremendous amounts of heat,in a very very small area. The pressure is great also in the beginning of the chamber/barrel. Also the heat from the powder is tremendously hot but doesn't effect the chamber/barrel to the degree friction does. My thinking has been with all the above is the receiver and barrel since being as thick as it is it's acting like a heat sink as it should but each time you load a new round you also allow a small rush of cooler air into the chamber.That cools the the chamber/barrel surface off quicker than the metal between it and the outside of the receiver/barrel.The more you shoot without it able to cool effectively the quicker it will happen especially in the winter and you're not giving the gun a "break" after a few rounds.More so with the more pressure that's developed as in "Hotter" loads etc. With all those forces combined and then have someone that treat their weapon well they'll find they have those problems much faster or more often (in many of their weapons). I've reloaded a lot of rounds,especially for my .243 Rem 788.I like and get better accuracy from IMR 4831 slow burn powder.The CUP is around 50/51,000 yet the fps is nearing 3,000. with 100gr Speer #1220.I haven't had to reload any in many years and don't have my data book at hand atm but I think it was around 41.7 or .9gr on our beam scale (digital scales weren't avail.yet back then or were ridiculously expensive). I haven't witnessed any problems yet with it but I only shoot 3 shots to see how it groups 2and let it cool..Just like hunting,the 1st shot is going to be out of a cold barrel and it should be the only one you need.You probably won't get more than 3 shots at your target (before it's gone if you miss).If you need to shoot more than twice at your target you shouldn't be shooting at that target to start with. BTW,thinking about it.Flywheels on vehicles get the same fire cracking and alligator skin.Friction (especially if one slips the clutch a lot) creates a lot of heat in short order.Then there is the centrifugal force trying to rip the flywheel apart. Your brake rotors will sometimes have the same problem.
the reason for the wear in that area is because that's where the most friction occurs because that's where the bullet is being compressed and rifling is being formed on the jacket
2.2 Chemical ablation The main process of chemical ablation is carburizing and oxidation. In the process of carburizing, the carbon spread from gas to the inner wall of the bubble and with the base metal to form solid solution. Excessive carbon promotes the precipitation of cementite, thereby reducing the toughness and melting point of the bore, resulting in the substrate being easily eroded by heat and mechanical factors. Similar to carburization, oxygen in the gunpowder gas can spread to the metal surface and oxidize it. Iron oxide will form a brittle surface of the flaky, easily formed into hot cracks and then be corroded. Besides carburizing and oxidation, many researchers suggested that hydrogen corrosion, hydrogen embrittlement and hydrogen induced cracks also play an important role in the ablation process. Underwood[3] compares laser pulse ablation with actual ablation of the sample and then found that laser pulse heating well simulated the actual ablation status in the coating hot melt, hot cracking and other aspects. However, the cracks in the base metal covered by the coating can’t be imitated. They think this is because there is hydrogen cracking in the actual ablation. Sopok[4] believes that the hydrogenation process is that the diffusion of hydrogen in the gun steel reduces the strength and toughness of the steel, and increases the risk of cracking and brittle failure. When hydrogen is absorbed through the unoxidized crack surface, the surface energy required for crack propagation is reduced.
Same principle as loading a lead bullet in a muzzleloader. After the first couple inches the rifling’s are formed into the bullet and the bullet slides easily down the rest of the barrel. Makes sense
One possible contributing factor you might include in your assessment (theory) is barrel harmonics, the resonance induced and its continuous affect on the various metals/coatings and processes being used.
@commonconservative putting aside your sarcasm... harmonics in conjunction with heat, pressure, and associated friction can lead to micro-delaminations of the barrel coatings and the metal itself. He touched on this phenomenon, called "Fire Cracking". I was just throwing in harmonics as a potential contributor to his wholistic theory.
Any test from fast/slow burning powder loaded to the same V0? The total working pressure during the barrel time most be better for the slow burning powder with lower pressure peek. (Flater and longer pressure curve) Acording too firecraks..
Nice theory and sounds good.. Though what do you thing about H2s stress cracking and erosion as a potential. Sulphide attack under temp and pressure is a well known phenomenon in Oil & Gas production system. Maybe something in this?
I agree with you that there is a chemical reaction molecularity going on in the throat area of the steel because of the pressure - it is more a chemical reaction in the throat than barrel vibrations. I think of it as more of a chemical etching. His hypothesis is interesting, but I can't go down the pressure road alone. Why does not the chamber area ever see this type of cracking if it is just pressure alone?
Yould be tested, just use an Iridium barrel, It shouldnt react with anything. I hesrd they used it in cannon vents and it didnt show signs of wear even after 3000 shots.
Be interesting to see barrel wear in a structured barrel . The erosion probably starts at the throat as the bullet is formed to the diameter of bore in a very short distance. The diameter of throat would increase as it wears and the bullet would continue to cause erosion further away from chamber. Great topic.
Pressure plus carbon from the fired round depositing in the stress cracks during firing. At the next firing the now carbon filled cracks expand (open) a bit more allowing more carbon to deposit in the cracks . It repeats to the point where you can see the ‘alligator skin’ . Some things make the situation worse like long heavy for caliber bullets that keep peak pressure over the throat area for a longer period of time.
Notice a road, that has some substantial wear, as it approaches a traffic light. The asphalt gets piled up as car after car “decelerates” to come to a stop. It begins to deform and crack after multiple repetitions ....ad in the hot and cold temps. And so it is with a bullet “accelerating” as the lands cut grooves into the bullet. Same process in reverse. Inertia and friction and heat are all at work. If I can figure out how to repave a rifle barrel I may get to retire early.
I wonder if making the chamber and first few inches of barrel thicker would help the stretch and or flex from the pressure spike may help with the fire cracking
Alternative thinking, there are people that run in a barrel buy shooting very low speed/ pressure bullets for the first 40 rounds, increasing speed/ pressure as they go to season the barrel. "They say" the barrel last's longer, but does it ? and if so by what percentage? Alternative thinking is how you make advances.
The highest amount of heat+pressure+friction happens in the first inches of the barrel. The highest amount of flexing of the metal is the result. So, just like an old rubber band will crack and scale as a result of expansion and collapsing, so does barrel metal.
Those kinds of cracks show up if a surface grinding operation is done overly aggressive. In that case, there is the friction of the wheel going against the steel, almost ripping it just as a bullet. And then the heat that is developed in the process. I think you’re on to it.
Even tho the bullet is moving slower at the beginning of it leaving the shell the reason it wears out more at the beginning of the barrel and not the end is bc by the time the bullet get to the end about to exit the barrel the first part of the rifling already put the groves into the copper jacket and the cracking is caused by heat plus, pressure,plus, friction,plus the cool down that would be by guess is why the cracking starts and why the beginning of the barrel wears out faster common sense just think about it
Trent I am with you as the throat rifling has to engrave the grooves in the bullet. This generates a lot of heat. However, I might add that metal having an elastic property, where the bullet engages the rifling a wave of metal (lands) is pushed ahead of the bullet. This would be greater as the bullet is being engraved at the throat. This can induce fatigue which can lead to checking/cracking.
Yes, M855 and bimetal bullets tend to be a bit harder on the barrel. Lucky gunner did an article on it and found bimetal cuts the barrel life down significantly compared to brass. The brass simply doesn't compress as well and requires more pressure to push down the barrel so it is harder on the bore.
Tldr, rounds that are smaller in diameter and move faster will wear out a barrel faster than if the round is larger in diameter and moves slower. Is that about right? How long would a lever action rifle chambered for 357 Magnum last then?
Have you checked to see if barrels at different thicknesses have this trend earlier or later? It could bring validity to your theory if you can find a pattern based on thickness and usage.
To primalrights, This is very interesting. Once fired, subsequent rounds will continue to accumulate residue in the barrel with greater potential for abrasive friction so cleaning more often may help. The friction from a bullet quickly pushed through a barrel with an hydraulic ram for example would heat up but the resistance is not overwhelming and the heat generated would be uniform but the bullet being much less mass than the barrel, would be the recipient of the greater share of that heat. I do not understand what you mean by a barrel being "shot-out". Is it only the throat, or is the rifling worn out, or is the barrel inside diameter to great to properly contain the pressure for the necessary velocity? If pressure, as you indicate, is the problem, how does the pressure affect larger relative outside barrel diameters using a Remington .223 extra thick barrel and extra short for example? How would this affect stainless steel for example? Consider the differences between gasoline and diesel engines where gas has a very high pressure for a short time and Diesel a lower pressure for a longer time. Different powders and different barrel lengths could optimize pressure so the gun will not experience that negative pressure that leads to chamber or barrel failure. A 5.56 military vs. a .223 or a 7.62 military vs. a .308 are potential examples of too much pressure in an unrated gun. One of the comments here mentions that heat-checking could be a result of the surface cooling or heating up faster or slower than the outer areas of the barrel. In aviation this is a serious problem, with air-cooled engines, where outer and inner surfaces cool at different rates, with detrimental results, requiring special alloys. Also, teacups as we all know survive better if they have thinner porcelain. We have seen tests where under continuous auto-fire a barrel will heat up red hot and it seems that heat build up in a short time is possible even if it is for many very minute periods of time. Heat transference in valves of gas engines even though making contact for an extremely short period of time, conduct more heat from the valve to the seat than up the stem. After the demise of unleaded gas the valve-seats were induction hardened so micro-pickup on valve surfaces would not occur. Also, Sodium filled valves proved ineffective as most of the heat transference.went to the seats not the stem. Anyway, once again, what do you mean by a barrel being shot out, if you have the fire-cracking and not shot-out if there is no fire-cracking, even if the throat is somehow worn out? Thanks in advance for your reply.
I do agree with your thoughts on this subject but what if Harmonics or frequency of a pressure wave meets the harmonics of the area of the barrel. Would this not cause A micro fissure similar to Tesla’s work on frequency. Just a thought?
Yes, but - (isn't that the way all responses start?). OK, so you delve into what causes the observable physical changes in the surface finish of the interior of the barrel, and talk about what can be done to change the rate at which the physical changes appear - but that's focusing on the appearance. The question is, what is it about a barrel that looks that way, that makes that barrel shoot poorly? Does the barrel distort and vibrate differently? Does the rifling no longer engaged the bullet and stabilize it properly, so you get increased dispersion shot-shot? Does the internal diameter of the barrel change, allowing gases to bypass the bullet and erode or overheat the bullet's surface, so that it loses concentricity with the barrel? Or do gases flowing around the bullet through the eroded throat tilt the bullet as it leaves the case mouth and enters the leade (we know that a similar effect takes place with gas tilting of boat tail bullets as they leave the muzzle)? I.E. does the erosion fail to keep the bullet axis aligned with the barrel axis, so that the bullet travels down and exits the barrel spiraling eccentrically (the point of the bullet describing a circle instead of a point at the center of a circle), leading to inconsistent travel to the target from aerodynamic effects? Seems to me that one way to test some of this would be to take a "shot-out" barrel and bore out the eroded throat, and then insert a "sleeve" - a tube of fresh metal in its place - one that would maintain the alignment of the bullet as it begins leaving the case on its way to engaging the rifling at the leade. A precision chambering reamer would ensure concentric alignment of the new throat with the cartridge and subsequent leade and rifling. It would then be possible to see if the heat checking observed in the leade and early rifling had the same deleterious effect once the bullet was set off on its way properly by a properly tight and aligned, and non-eroded throat, as it left the mouth of the cartridge case. The result could lead to a change in the way we look at these things if so; barrels might be built with replaceable sleeves, or sleeves made of a different, less-erodable alloy - one that didn't degrade in the hot chemical and hammering, high-pressure thermomechanical environment of the cartridge mouth, like a tantalum or hafnium carbide or a tungsten, titanium, or tantalum-based sleeve. It could be an esoteric alloy that would be too expensive to make a barrel out of, but perfectly affordable in a relatively tiny, thin, inserted sleeve the size of a chamber's throat. If, that is, bullet misalignment as a result of throat erosion and burning gas/powder forces on the bullet proved to be the source of the problem. You'd certainly think that an overbore and sleeve job would cost a lot less than a new barrel - and might even be done without having to remove the barrel from the receiver, lowering gunsmith costs - if the idea proved out. Interesting premise and thought-provoking video!
Heat, Heat, Heat! Everything that goes through a barrel is far softer than the barrel. Heat (from gas, pressure and friction) changes the molecular composition of the barrel metal (erosion). Have you ever seen "firecracking" or "alligator"...? That is a heat indicator. Have you ever seen an eroded gas port... this is a visual representation of a molecular change, due to heat by all contributing factors (again, gas, pressure and friction).
Reasonably informed, serious, armchair physics has to agree with everything you say. I see it this way. From the physics of high explosives, it's been determined that the shockwave from any high explosive, is exponentially harder than steel. If that wasn't so, explosives couldn't rip steel to shreds. The shockwave confined within a chamber along with the intense heat, can be seen as high temperature, extremely high pressure hammer forging. The inner layers of the chamber are being hammer forged against the outer, cooler, material of the barrel. There are no materials (Adamantium?) that can withstand these forces and remain unchanged.... I think you're onto something.
How can I reduce pressure though then? lighter bullets with less charge behind it? I cannot replace a barrel because here in south africa, replacing a barrel has nearly the same amount of hoops to jump through as with getting a new gun license (a 4 month waiting time PLUS hoping you get approved by the central firearm registry... which doesnt always happen)
Might it make sense to start smooth and begin rifling mid-barrel? Sure would like to see a total energy vs (x, v or t). Start plot with the potential energy of the propellant through PV=nRT, Angular momentum (energy), mv^2 energy, frictional energy, bypass energy, exhaust energy, convection wall loss, etc. All on one plot vs time or vs bullet position down the barrel or vs bullet speed? What effect variable rifling on accuracy? Such a plot, even if notional, might be invaluable to invention?
Smooth to rifling transition is called freebore....too much freebore causes too much bullet jump to the rifling and a loss of accuracy as well as lower velocities so is not a good option. Variable rifling or Gain Twist as it is called, is a process that is now utilized by some barrels makers to help ease the rifling being engraved into the bullet. Gain Twist is better than excessive freebore.
I agree with your analysis and evaluation😉😎 could it be that the initial rifling wear is primarily influenced by pressure in the first area of the rifle after the bullet travels the barrel and friction is the major influenced to rifling wear towards the end of the rifling due to the highest velocity.
Here is an article that will shed some light on this theory by the Australian Dept. Of Defense. "Understanding Gun Barrel Erosion". By Ian A.Johnston. DTSO - TR -1757.
Sorry I did not place my comments in order but if you read from 2.1 (which is three down) to 2.3 you will get the basis of the causes of barrel wear and in what order of significance.
Perhaps it's high pressures and heat "sandblasting" the barrel throat with particles and unburned powder. Thr hotter (softer) the metal the more the blasting wears it.. just talking, I don't know shit about this topic really.... edit: finishing watching your video and you are saying some of the same stuff I said but more.
It is due to heat generated by the friction die to inertia of the bullet, engaging the rifling while still not rotating on its axis.Additionally, the area is full of residues of unburned powder which increases friction, otherwise if this is due to corrosive gunpowder used, would be interesting spraying only one out of two rifles after shooting same amount of rounds, an Ar15 could be a good test.
this is a great video but you said "everyone knows how a firearm works" haha these days its quite clear some ppl have no clue what firearms are let alone how they work. its a sad day for us gun lovers and love for mechanical function of firearms. but i get what you mean i just thought it was funny. good stuff
Plausible theory. We may well never know the answer. Very little pure research done on hand held weapons. This would be purely research for science sake. The solution is easy, but not practicable or marketable, simply load lighter loads. It is common knowledge that high velocity, high pressure cartridges burn out barrels much faster. Check out barrel life for a 22 Nosler or 22-250. How many 22 rimfire barrels have been changed due to being burned out? I have access to a Winchester 22 pump model 1890, built in 1929, was given to my grandfather by his father, I have helped shoot tens of thousands of rounds through this rifle, all of my uncle's and cousin's learned to shoot with it. Still shoots as accurate today as it did when I first used it over 50 years ago.
Good theory! But I´ve got two points: 1. Isn´t friction the greatest right at the start of the rifleling, where the rifleling gets engrevated into the bullet? 2. And in addtion to your theory steel gets weaker when it is hot, so the pressure could attack easier. It seems to me that firecracking occurs earlier when a barrel gets shot often very hot.... Would love to read your thouths! Greetings from germany
I've seen heat cracking like that on brake rotors. It looks almost the same.
Look up "Heat checking" very common in hardened tool steel. Used in casting. The surface can be heated to 1400°f in 1/1000 of a second the metal expands on the surface but just a few thousands deep. This sets up stress between the cooler metal and the hot metal. And bam stress cracks. The gasses cool some as they travel down the barrel so the is less the father you go. Plus the other things going on in the chamber also.
I agree 100%. I think the problem started when long range and bench rest shooters' messages were heard in a broader audience. They like to ditch a barrel that won't provide sub- 1/4" groups consistently. I also believe how one cleans a rifle makes a large impact. I scrub down my rifle and have been told well, you're making the bore larger, ummm ok, but I am still within SAMMI specs if I do. The bullet will expand to close those gaps due to the higher pressure. I also have a barrel that is well cleaned which doesn't look like it has 1100 rounds on it and it's a 6.5CM. The throat still looks new. You can't even see the alligator skin pattern until you're 4" past the throat. The carbon ring on the neck MUST be removed after every round of firing or you increase pressures by up to 4k psi. Lou Murdica has proven this in his testing. I just don't buy that a $1k barrel should be thrown away, because it has some erosion early in the bore. If that bullet is still capable of stabilization and not tumbling when it hits the target, then the barrel is still good in my opinion. If I have a 1:7.5 twist barrel and loose 6" of a 26" barrel to erosion, I still have enough barrel and twists to stabilize at least a 147gn bullet. In fact I'd argue that barrel can still stabilize any bullet requiring a 1:8 twist. Damn good info sir!
My cousin bought a 100+ years old 44-40 Marlin. It shot just over 1 MOA groups at 25yards. I wanted to test my new borescope and we were schocked by the amount of not only throat erosion but also previous rust marks on the rifling. The previous owner took great care of the rifle, but the couple of owners (some of them government/army) obviously didn’t. Regardless, the rifle defied all logic and still shot remarking well.
You are on the right track. The comparison you are looking for is a laser on the surface of steel. It is the pressure affecting he surface of the metal, and its is not the contraction creating the alligator fractures, it is the cool down. Imagine blasting the surface of the metal with a laser to extreme high temperatures, the molecules on the surface expand rapidly, the pressure is relieved in microseconds, suddenly cooling the surface. The material just behind the surface soaked the heat, but the material on the surface is cooling faster. So as the barrel is trying to go back to its original shape (from expansion) with the surface cooling faster, it creates micro fractures. The surface metal fatigue looses elasticity over time, and thus the cracks stay, and the barrel is worn out as metal elasticity has left the area.
Spot on all the way. one other thing is the expansion and contraction of the surface of the boor through heating and cooling actually hardens the surface and makes it brittle thus starting the cracking process.
So an analogy to a layman might be the hot sun drying the first 1/4" inch of mud on dry lake bed?
@mikelong9638 and also lips cracks from drying out of cold. Outer skin lost elasticity. While inner flesh is still elastic. Outer skin trying to conform to moving elastic flesh cracks...
Excellent video. Thought provoking and probably right. I watched this as part of my search for answers to why my once very accurate rifle suddenly became very inaccurate. I suspect throat erosion and have a bore scope on the way to find out. I believe the exact cause of throat erosion is relevant. I might want to prolong barrel life, and if reducing pressure is the key to that, then that would inform me to reduce my handloads a bit...or a lot!
If the cost factor to make a barrel/load combo advantageous to the industry, then it shall be. Right now, we are living with it. Great, seamless presentation. Please keep it up! Mark Richardson
In response to your comment regarding "others smarter than myself", my sense is that tough there maybe others more educated, I doubt that there are many that are smarter. Great video.
It’s really refreshing to hear from somebody that thinks about something in depth and draws conclusions based on evidence, and is open to changing their opinions or theories. Imagine how much more advanced our society would be if more people took this approach as opposed to the more common approach: “This is what I believe, you cannot change my mind because I know I’m right. No I’m not going to test this myself and I’m going to ignore all evidence presented to me that says otherwise”.
additionally to your explanation I would add what is bullet inertia along spinning axel.
it takes most stress on barrel rifling in first few inches to overcom bullet inertia and start bullet spinn . once bullet is in spinning motion riflings are subjected to less stress therefore less erosion further down in the barrel
the bore conditions kit that David Tubbs sells will polish the lake bed metal and rough tool marks in the throat and keep it running longer. I did a treatment on an M1a and it shot better groups. great video, make sense to me
I really appreciate the reasonable explanation of the cause of barrel damage. I agree, pressure would be, in my mind, the primary cause of pressure damage. The question in my mind is what can cause normal pressures to become barrel killers? I have three theories: 1. Poor barrel care caused by lack of keeping the barrel free from too much fouling, including powder residue and especially copper fouling. These obviously cause a degree of blockage in the barrel the bullet has to overcome when its fired. Thus, higher pressures. 2. Firing too heavy a bullet from smaller powder charges due to case capacity. I have a .308 Win in a model 99 Savage that I bought from a former client. From day one this rifle could't group anything less that a foot spread at 50 yards. I know the previous owner fired mostly 180 grain bullets from this rifle. I had a gunsmith clean copper fouling from the barrel. Still, no accuracy what-so-ever. I bought a bore scope and voila, I found the barrel is heat cracked most of the length of the barrel. In my opinion, due to lack of cleaning and using a bullet too heavy for the case capacity powder charge the barrel is history. 3. Poor quality of the steel used in the barrel. This is hard for anyone to judge. But, the model 99 Savage was a very expensive rifle to manufacture. My theory is, Savage started to take shortcuts in the manufacture to reduce their costs of manufacture. For this particular model year, not too long after, Savage discontinued this iconic weapon. I am currently trying to find someone to lathe a new barrel to fit the receiver or re-bore the barrel to either a .338 Federal or .358 Winchester. My thought is, with a larger bore and using no bullet heavier than 180 grs., plus my fussiness in keeping my barrels clean (very little brass brush as possible, if any) I should be able to get a very accurate rifle. I could retire the rifle but I don't want to have a useless weapon in my collection. I am open to the thoughts of others including Greg's.
2.3 Mechanical wear
After the heat and the chemical effect, the base metal is prone to heat softening, mechanical strength
and crack, etc. The friction generated during the coupling process is sufficient to consume the part
of the matrix material. This is the main way of mechanical wear. In addition, due to unburned
propellant particles and the high-speed movement of the peeling produced by ablation, the
mechanical erosion of the bore is also great.
It is mostly heat. I used to repair light and heavy machineguns. It is nothing to see large chunks of lands missing from the breech end of the barrel. That is why many machinegun barrels have about an 8" stellite liner in them. Chrome lined barrels have less than .001 thick coating on a wall and pressure would crack that chrome quickly. I have seen old chrome lined barrels with tens of thousands of rounds through them and they look good yet.
there is a measure of friction called a P/V value. it is a measure of pressure related to velocity, both factors in friction
Boat tail bullets make the problem worse, the base funnels gases ahead of the bullet making a very hot plasma torch prior to the bullet movement and the bullet then hits it.
Excellent discussion. I believe that you're partly right, in that pressure plays a role; but the cause also has to include the fire/heat from burning powder- or the firecracking wouldn't be most pronounced at the case mouth/leade, & progressively diminish towards the muzzle.
I realize that society typically thinks in a "just get a new one" mindset.....but I'm much more interested in the "what can we do to restore it?" line of thinking.
Have you seen heat cracks in break rotors? Its from heat, friction, and pressure
A combination of all three. Add to that the bullet being compressed has to expand the barrel to some degree.
An excellent hypothesis, you really are onto something and I have to agree with you! Stainless and chrome moly barrels, for example, are compressible and indeed some are made by cold forging. Heating them up will only increase the amount they will compress. I have noticed a similar effect to fire-cracking when hammering brittle steel.
Never stop thinking and questioning the excepted norm!
Partially burned and burning powder granules impinge upon steel in a high pressure, high temperature environment sand blasts the lead of the barrel. The amount and type of powder makes the difference. Slow burning powder confined by the overbore is like a sandblasting torch. I shoot a 300 BO 100 yd target rifle with 1400 rds. thru it. barrel looks like new. Doesn't seem to be a problem with pistols.
Again, great video. We also must consider what's going on in front of the bullet. Tremendous pressure there as well. That bullet, and all the pressure behind it, is asking air in front of the bullet to get out of the way very rapidly, which it can't, which produces resistance or drag. Obviously the drag is overcome or bullets wouldn't leave barrels. But there's that bullet, in between two competing forces, vast amounts of pressure fore and aft. Something's gotta give...barrels, especially at the throat. Bullets, too. But I wonder about the malleability differences between softer jacketed lead and solid copper bullets which I now use and must use in California. One of my once very accurate rifles recently became inaccurate. I switched to nonleaded bullets 7 years ago in that rifle. And my handloads are pretty stout. Can anyone else corroborate this?
Got me thinking - a dangerous thing. If you are correct then a worn out barrel may only be worn out in the stressed area. Removal of the chamber and damaged fire cracked throat ( if the remaining steel were available - length/OD etc) and the barrel is then re chambered the barrel may well be sound again - within limits. If the barrel IS sound again then I pose two questions:-
1/ Is the barrel worn out because it is damaged?
or
2/ Does the fire cracked throat impose damage on the projectile at firing.This may make the projectile not uniform or not stable in the barrel and/or in the air on exit and on its way to target?
Some thing to keep us awake at night.
Hydrogen ( powder hi temp. decomposition byproduct)saturates the steel at Hi pressure and makes it brittle. The Hi temperature is another major factor. The way to mitigate the throat erosion is to use "cold" powders like a nitrocellulose powders with lowest nitroglycerin content possible or without it. + There are some different powder formulations with nitroguanidine compound. It's all traced back to the research about barrels in artillery pieces that was done after ww1. I can't remember exactly where I red about it.
Makes absolute sense, what is a primary test for all barrels? PSI. A prime focus of SAAMI criterion is to publish acceptable chamber pressure. A common theme of warnings of firearms producers is not to exceed the rated PSI. When PSI is a constant topic of concern across all aspects of the industry, it's as was stated in the video; "academic" to understanding why, how and what it is that causes barrels to fail, whether it's suddenly and catastrophically or over time...
I am not an engineer, but it makes rational sense to me that the most stress imposed on the metal is the explosion at the throat of a barrel, aka the chamber. Other than having an obstruction in the barrel, the only place you see guns exploding is at that location. If a powder charge exceeds the safe threshold of the firearm, this is not the weakest link, it is just the place where it is most likely to be realized and immediately.
There are many gunsmiths that agree with u. And if u consider the anecdotal evidence of high capacity or over bore cartridges accelerating barrel wear, in comparison to smaller cartridges.. it makes perfect sense as the whole point of the excess powder burning at a reduced speed is to prolong the pressure wave behind the bullet as it travels down the tube. One way or another, if u want performance it always comes at the price of longevity.
It is relevant if you want a barrel to last longer than it takes to find a load that works for it and if you want to innovate the field to make progression in shooting sports... Heat is also generated through vibration from the pressure and barrel harmonics...
I have a custom rifle barrel that I had cut with a 4 inch shank with a diameter of 1.3 inches, rifled for a 7mm wildcat... I have shot over 350 rounds in the rifle and the lands have yet to move... The coal is around 3.6 inches and the lands are well within the 4 inches of shank...
I also have a steep shoulder angle of 35 degrees that may contribute to throat life, but this barrel has outlasted the last one I had built by a long shot...
Interesting. I thought engineers where onto that because of the bulge you see in the barrel chamber area. If you have a way of measuring barrel expansion at detonation that would be an interesting info.
WOW... That is a trip.. I have never put any thought into the "How long does a barrel last?".. That answer blew my doors off, as I had always conceptualized that in "round count pending the caliber"... MIND BLOWING... Well, I know what I am gonna be talking about all day today, and the next month with the club... I hope you know, I am gonna claim your statement as my own, as if I thought of that clever way to say that..LOL... Just kidding...
I agree with you. I think a simple explanation is acseleration. When the bullet is launching, it moves the metal in the barrel, because its getting so much force. Its the same in dragracing. It rippels the surface, because of the violent aceseleration.
Ball powders cause less erosion than log powders, which are tumbling through the bore according to a couple of sources I've seen. Rates of fire are a factor as the hotter the barrel gets, the more susceptible it is to erosion. Cryogenic treated barrels are tougher, and there are also better steels. Speer reloading experiments showed calibers like 264 win mag was burning out barrels in unde 300 rounds. This applies to over bored short magnums. Pressure is definitely the main problem. This is also supported by Randy Selby, the gunsmith.
Sounds like the surface of the bore is work hardening while the subsurface is still ductile.
The work hardened bore surface can't handle the bore expansion without checking.
2.1 Heat ablation
Among the various factors that cause damage to the inner chamber, the heat effect is the primary
and fundamental. The individual effects of the heat factor can lead to three kinds of failure
phenomena: the thermal softening of the body surface; the thermal transformation of the bore wall;
the melting of the surface. When the gun is fired, the volume of the material on the surface of the
chamber is alternately expanded and contracted by rapid heating and cooling, and a sharp phase
change occurs at the same time. The high temperature environment provides favorable conditions
for the chemical reaction between the gunpowder gas and the metal in the borehole wall. The
resulting white layer, such as Fe3C, will melt under heat and be removed by high-speed gunpowder
gas to accelerate the inner chamber failure process. Melting ablation is the fastest and most severe
ablation mechanism that causes the inner bore to be destroyed, which is particularly pronounced in
high-bore large caliber artillery. Meanwhile, the heat can also cause the tube thermal stress, thermal
bending and other undesirable phenomena, which affect the use of artillery performance on some
degree. So the heat problem has aroused people's attention for a long time, and becomes a necessary
factor in the design of artillery.
Great job! Thanks. You are right that there is not much info on this subject.
It's not often anymore you see people using their brain and commonsense at the same time.
I've thought the same for many many years,probably since my mid/late teens when I then was reloading for a few years already.
Like you say,the friction creates tremendous amounts of heat,in a very very small area.
The pressure is great also in the beginning of the chamber/barrel.
Also the heat from the powder is tremendously hot but doesn't effect the chamber/barrel to the degree friction does.
My thinking has been with all the above is the receiver and barrel since being as thick as it is it's acting like a heat sink as it should but each time you load a new round you also allow a small rush of cooler air into the chamber.That cools the the chamber/barrel surface off quicker than the metal between it and the outside of the receiver/barrel.The more you shoot without it able to cool effectively the quicker it will happen especially in the winter and you're not giving the gun a "break" after a few rounds.More so with the more pressure that's developed as in "Hotter" loads etc. With all those forces combined and then have someone that treat their weapon well they'll find they have those problems much faster or more often (in many of their weapons).
I've reloaded a lot of rounds,especially for my .243 Rem 788.I like and get better accuracy from IMR 4831 slow burn powder.The CUP is around 50/51,000 yet the fps is nearing 3,000. with 100gr Speer #1220.I haven't had to reload any in many years and don't have my data book at hand atm but I think it was around 41.7 or .9gr on our beam scale (digital scales weren't avail.yet back then or were ridiculously expensive).
I haven't witnessed any problems yet with it but I only shoot 3 shots to see how it groups 2and let it cool..Just like hunting,the 1st shot is going to be out of a cold barrel and it should be the only one you need.You probably won't get more than 3 shots at your target (before it's gone if you miss).If you need to shoot more than twice at your target you shouldn't be shooting at that target to start with.
BTW,thinking about it.Flywheels on vehicles get the same fire cracking and alligator skin.Friction (especially if one slips the clutch a lot) creates a lot of heat in short order.Then there is the centrifugal force trying to rip the flywheel apart.
Your brake rotors will sometimes have the same problem.
I just watched this again. Your term "mudcracking" is an accurate description. I can't think of anyplace else where you see a similar phenomenon?
the reason for the wear in that area is because that's where the most friction occurs because that's where the bullet is being compressed and rifling is being formed on the jacket
Heat, pressure & friction. What else is there?
2.2 Chemical ablation
The main process of chemical ablation is carburizing and oxidation. In the process of carburizing,
the carbon spread from gas to the inner wall of the bubble and with the base metal to form solid
solution. Excessive carbon promotes the precipitation of cementite, thereby reducing the toughness
and melting point of the bore, resulting in the substrate being easily eroded by heat and mechanical
factors. Similar to carburization, oxygen in the gunpowder gas can spread to the metal surface and
oxidize it. Iron oxide will form a brittle surface of the flaky, easily formed into hot cracks and then
be corroded. Besides carburizing and oxidation, many researchers suggested that hydrogen
corrosion, hydrogen embrittlement and hydrogen induced cracks also play an important role in the
ablation process. Underwood[3] compares laser pulse ablation with actual ablation of the sample and
then found that laser pulse heating well simulated the actual ablation status in the coating hot melt,
hot cracking and other aspects. However, the cracks in the base metal covered by the coating can’t
be imitated. They think this is because there is hydrogen cracking in the actual ablation.
Sopok[4] believes that the hydrogenation process is that the diffusion of hydrogen in the gun steel
reduces the strength and toughness of the steel, and increases the risk of cracking and brittle failure.
When hydrogen is absorbed through the unoxidized crack surface, the surface energy required for
crack propagation is reduced.
Ok for 4" wear from breech end. What about the wear at 4" muzzle end? Where does it come from?
Same principle as loading a lead bullet in a muzzleloader. After the first couple inches the rifling’s are formed into the bullet and the bullet slides easily down the rest of the barrel. Makes sense
Have a couple 220 swifts that have brought the end to thousands of rock chucks. The first 4 " of both barrels are gone. Still are half minute guns..
One possible contributing factor you might include in your assessment (theory) is barrel harmonics, the resonance induced and its continuous affect on the various metals/coatings and processes being used.
@commonconservative putting aside your sarcasm... harmonics in conjunction with heat, pressure, and associated friction can lead to micro-delaminations of the barrel coatings and the metal itself. He touched on this phenomenon, called "Fire Cracking". I was just throwing in harmonics as a potential contributor to his wholistic theory.
@commonconservative ...so nothing to contribute, on topic?
Excellent! How can I use a bore scope to evaluate the throat and lands of a rifle? Can you show us specifically fire-cracking in another video?
Any test from fast/slow burning powder loaded to the same V0? The total working pressure during the barrel time most be better for the slow burning powder with lower pressure peek. (Flater and longer pressure curve)
Acording too firecraks..
Nice theory and sounds good.. Though what do you thing about H2s stress cracking and erosion as a potential. Sulphide attack under temp and pressure is a well known phenomenon in Oil & Gas production system. Maybe something in this?
I agree with you that there is a chemical reaction molecularity going on in the throat area of the steel because of the pressure - it is more a chemical reaction in the throat than barrel vibrations. I think of it as more of a chemical etching. His hypothesis is interesting, but I can't go down the pressure road alone. Why does not the chamber area ever see this type of cracking if it is just pressure alone?
Yould be tested, just use an Iridium barrel, It shouldnt react with anything.
I hesrd they used it in cannon vents and it didnt show signs of wear even after 3000 shots.
Be interesting to see barrel wear in a structured barrel . The erosion probably starts at the throat as the bullet is formed to the diameter of bore in a very short distance. The diameter of throat would increase as it wears and the bullet would continue to cause erosion further away from chamber. Great topic.
This was a great video. Thank you for you knowledge.
Pressure plus carbon from the fired round depositing in the stress cracks during firing. At the next firing the now carbon filled cracks expand (open) a bit more allowing more carbon to deposit in the cracks . It repeats to the point where you can see the ‘alligator skin’ .
Some things make the situation worse like long heavy for caliber bullets that keep peak pressure over the throat area for a longer period of time.
I agree! People get on these know it all bandwagons and just run with incorrect data.
Notice a road, that has some substantial wear, as it approaches a traffic light. The asphalt gets piled up as car after car “decelerates” to come to a stop. It begins to deform and crack after multiple repetitions ....ad in the hot and cold temps. And so it is with a bullet “accelerating” as the lands cut grooves into the bullet. Same process in reverse. Inertia and friction and heat are all at work. If I can figure out how to repave a rifle barrel I may get to retire early.
That's called "shoving", and it's caused by using too small of an aggregate in the hot mix asphalt...
I wonder if making the chamber and first few inches of barrel thicker would help the stretch and or flex from the pressure spike may help with the fire cracking
Alternative thinking, there are people that run in a barrel buy shooting very low speed/ pressure bullets for the first 40 rounds, increasing speed/ pressure as they go to season the barrel. "They say" the barrel last's longer, but does it ? and if so by what percentage? Alternative thinking is how you make advances.
The highest amount of heat+pressure+friction happens in the first inches of the barrel. The highest amount of flexing of the metal is the result. So, just like an old rubber band will crack and scale as a result of expansion and collapsing, so does barrel metal.
Slowest powder possible for bullet weight to slow the bell curve
Expension due to pressure should vary from smaller to larger diameters of the barrel. Have you experiance in different diameters?
Those kinds of cracks show up if a surface grinding operation is done overly aggressive. In that case, there is the friction of the wheel going against the steel, almost ripping it just as a bullet. And then the heat that is developed in the process. I think you’re on to it.
Hey question, i have wierd wear patterns on the outside of my m2 carbine barrel. It looks like worm wood. Average blue color with raw metal color
Even tho the bullet is moving slower at the beginning of it leaving the shell the reason it wears out more at the beginning of the barrel and not the end is bc by the time the bullet get to the end about to exit the barrel the first part of the rifling already put the groves into the copper jacket and the cracking is caused by heat plus, pressure,plus, friction,plus the cool down that would be by guess is why the cracking starts and why the beginning of the barrel wears out faster common sense just think about it
Trent I am with you as the throat rifling has to engrave the grooves in the bullet. This generates a lot of heat.
However, I might add that metal having an elastic property, where the bullet engages the rifling a wave of metal (lands) is pushed ahead of the bullet. This would be greater as the bullet is being engraved at the throat. This can induce fatigue which can lead to checking/cracking.
Does bimetal bullets hurt your barrel?
Yes, M855 and bimetal bullets tend to be a bit harder on the barrel. Lucky gunner did an article on it and found bimetal cuts the barrel life down significantly compared to brass. The brass simply doesn't compress as well and requires more pressure to push down the barrel so it is harder on the bore.
so for hand loading for say .308 how should the rounds be loaded to extend the life of the barrel ?
What if you make that first few inches of the barrel thicker than the rest of the barrel?
Tldr, rounds that are smaller in diameter and move faster will wear out a barrel faster than if the round is larger in diameter and moves slower. Is that about right? How long would a lever action rifle chambered for 357 Magnum last then?
Have you checked to see if barrels at different thicknesses have this trend earlier or later? It could bring validity to your theory if you can find a pattern based on thickness and usage.
Have you observed a difference in cracking between a 30-30 a 30 odd 6 and a 300 Winchester magnum.
To primalrights, This is very interesting. Once fired, subsequent rounds will continue to accumulate residue in the barrel with greater potential for abrasive friction so cleaning more often may help. The friction from a bullet quickly pushed through a barrel with an hydraulic ram for example would heat up but the resistance is not overwhelming and the heat generated would be uniform but the bullet being much less mass than the barrel, would be the recipient of the greater share of that heat. I do not understand what you mean by a barrel being "shot-out". Is it only the throat, or is the rifling worn out, or is the barrel inside diameter to great to properly contain the pressure for the necessary velocity? If pressure, as you indicate, is the problem, how does the pressure affect larger relative outside barrel diameters using a Remington .223 extra thick barrel and extra short for example? How would this affect stainless steel for example? Consider the differences between gasoline and diesel engines where gas has a very high pressure for a short time and Diesel a lower pressure for a longer time. Different powders and different barrel lengths could optimize pressure so the gun will not experience that negative pressure that leads to chamber or barrel failure. A 5.56 military vs. a .223 or a 7.62 military vs. a .308 are potential examples of too much pressure in an unrated gun. One of the comments here mentions that heat-checking could be a result of the surface cooling or heating up faster or slower than the outer areas of the barrel. In aviation this is a serious problem, with air-cooled engines, where outer and inner surfaces cool at different rates, with detrimental results, requiring special alloys. Also, teacups as we all know survive better if they have thinner porcelain. We have seen tests where under continuous auto-fire a barrel will heat up red hot and it seems that heat build up in a short time is possible even if it is for many very minute periods of time. Heat transference in valves of gas engines even though making contact for an extremely short period of time, conduct more heat from the valve to the seat than up the stem. After the demise of unleaded gas the valve-seats were induction hardened so micro-pickup on valve surfaces would not occur. Also, Sodium filled valves proved ineffective as most of the heat transference.went to the seats not the stem. Anyway, once again, what do you mean by a barrel being shot out, if you have the fire-cracking and not shot-out if there is no fire-cracking, even if the throat is somehow worn out? Thanks in advance for your reply.
So your saying if I take my 32 special put the bullet in the muzzle end and it goes to the brass it doesnt mean its worn out
If it is the pressure, why aren't chambers and bolt faces fire cracked? Checkmate.
It is heat cycling that does it.
I do agree with your thoughts on this subject but what if Harmonics or frequency of a pressure wave meets the harmonics of the area of the barrel. Would this not cause A micro fissure similar to Tesla’s work on frequency. Just a thought?
Yes, but - (isn't that the way all responses start?). OK, so you delve into what causes the observable physical changes in the surface finish of the interior of the barrel, and talk about what can be done to change the rate at which the physical changes appear - but that's focusing on the appearance. The question is, what is it about a barrel that looks that way, that makes that barrel shoot poorly? Does the barrel distort and vibrate differently? Does the rifling no longer engaged the bullet and stabilize it properly, so you get increased dispersion shot-shot? Does the internal diameter of the barrel change, allowing gases to bypass the bullet and erode or overheat the bullet's surface, so that it loses concentricity with the barrel?
Or do gases flowing around the bullet through the eroded throat tilt the bullet as it leaves the case mouth and enters the leade (we know that a similar effect takes place with gas tilting of boat tail bullets as they leave the muzzle)? I.E. does the erosion fail to keep the bullet axis aligned with the barrel axis, so that the bullet travels down and exits the barrel spiraling eccentrically (the point of the bullet describing a circle instead of a point at the center of a circle), leading to inconsistent travel to the target from aerodynamic effects?
Seems to me that one way to test some of this would be to take a "shot-out" barrel and bore out the eroded throat, and then insert a "sleeve" - a tube of fresh metal in its place - one that would maintain the alignment of the bullet as it begins leaving the case on its way to engaging the rifling at the leade. A precision chambering reamer would ensure concentric alignment of the new throat with the cartridge and subsequent leade and rifling. It would then be possible to see if the heat checking observed in the leade and early rifling had the same deleterious effect once the bullet was set off on its way properly by a properly tight and aligned, and non-eroded throat, as it left the mouth of the cartridge case.
The result could lead to a change in the way we look at these things if so; barrels might be built with replaceable sleeves, or sleeves made of a different, less-erodable alloy - one that didn't degrade in the hot chemical and hammering, high-pressure thermomechanical environment of the cartridge mouth, like a tantalum or hafnium carbide or a tungsten, titanium, or tantalum-based sleeve. It could be an esoteric alloy that would be too expensive to make a barrel out of, but perfectly affordable in a relatively tiny, thin, inserted sleeve the size of a chamber's throat. If, that is, bullet misalignment as a result of throat erosion and burning gas/powder forces on the bullet proved to be the source of the problem. You'd certainly think that an overbore and sleeve job would cost a lot less than a new barrel - and might even be done without having to remove the barrel from the receiver, lowering gunsmith costs - if the idea proved out.
Interesting premise and thought-provoking video!
Heat, Heat, Heat! Everything that goes through a barrel is far softer than the barrel. Heat (from gas, pressure and friction) changes the molecular composition of the barrel metal (erosion). Have you ever seen "firecracking" or "alligator"...? That is a heat indicator. Have you ever seen an eroded gas port... this is a visual representation of a molecular change, due to heat by all contributing factors (again, gas, pressure and friction).
Reasonably informed, serious, armchair physics has to agree with everything you say. I see it this way. From the physics of high explosives, it's been determined that the shockwave from any high explosive, is exponentially harder than steel. If that wasn't so, explosives couldn't rip steel to shreds. The shockwave confined within a chamber along with the intense heat, can be seen as high temperature, extremely high pressure hammer forging. The inner layers of the chamber are being hammer forged against the outer, cooler, material of the barrel. There are no materials (Adamantium?) that can withstand these forces and remain unchanged.... I think you're onto something.
Being a machinist , never thought of this
How can I reduce pressure though then? lighter bullets with less charge behind it? I cannot replace a barrel because here in south africa, replacing a barrel has nearly the same amount of hoops to jump through as with getting a new gun license (a 4 month waiting time PLUS hoping you get approved by the central firearm registry... which doesnt always happen)
Might it make sense to start smooth and begin rifling mid-barrel? Sure would like to see a total energy vs (x, v or t). Start plot with the potential energy of the propellant through PV=nRT, Angular momentum (energy), mv^2 energy, frictional energy, bypass energy, exhaust energy, convection wall loss, etc. All on one plot vs time or vs bullet position down the barrel or vs bullet speed? What effect variable rifling on accuracy? Such a plot, even if notional, might be invaluable to invention?
Smooth to rifling transition is called freebore....too much freebore causes too much bullet jump to the rifling and a loss of accuracy as well as lower velocities so is not a good option.
Variable rifling or Gain Twist as it is called, is a process that is now utilized by some barrels makers to help ease the rifling being engraved into the bullet. Gain Twist is better than excessive freebore.
I agree with your analysis and evaluation😉😎 could it be that the initial rifling wear is primarily influenced by pressure in the first area of the rifle after the bullet travels the barrel and friction is the major influenced to rifling wear towards the end of the rifling due to the highest velocity.
Outstanding Logic I agree 100%
i will think barrel wipe will also add to show crack near to the action.
ADD microcrystalization of the steel surface .
Thanks man!! Great video!
Here is an article that will shed some light on this theory by the Australian Dept. Of Defense.
"Understanding Gun Barrel Erosion". By Ian A.Johnston.
DTSO - TR -1757.
Sorry I did not place my comments in order but if you read from 2.1 (which is three down) to 2.3 you will get the basis of the causes of barrel wear and in what order of significance.
Heat. It doesnt matter if it's a rifle barrel or a tool bit on a CNC machine. Heat (over time) breaks down metals.
Does your theory apply to rifles with chromed barrels ?
A revolver has an extremely long throat band new and shoots well.
Great explanation
Makes sense to me!
Your theory is sound, so how do we get around it? There's gotta be a way to minimize it, if not eliminate it completely...
Stop shooting?
Good stuff.
Perhaps it's high pressures and heat "sandblasting" the barrel throat with particles and unburned powder. Thr hotter (softer) the metal the more the blasting wears it.. just talking, I don't know shit about this topic really.... edit: finishing watching your video and you are saying some of the same stuff I said but more.
Good job man
great vid.
It is due to heat generated by the friction die to inertia of the bullet, engaging the rifling while still not rotating on its axis.Additionally, the area is full of residues of unburned powder which increases friction, otherwise if this is due to corrosive gunpowder used, would be interesting spraying only one out of two rifles after shooting same amount of rounds, an Ar15 could be a good test.
Shooting slower = longer barrel life
this is a great video but you said "everyone knows how a firearm works" haha these days its quite clear some ppl have no clue what firearms are let alone how they work. its a sad day for us gun lovers and love for mechanical function of firearms. but i get what you mean i just thought it was funny. good stuff
Great Video!!!!!
Heat and pressure
Plausible theory. We may well never know the answer. Very little pure research done on hand held weapons. This would be purely research for science sake. The solution is easy, but not practicable or marketable, simply load lighter loads. It is common knowledge that high velocity, high pressure cartridges burn out barrels much faster. Check out barrel life for a 22 Nosler or 22-250. How many 22 rimfire barrels have been changed due to being burned out? I have access to a Winchester 22 pump model 1890, built in 1929, was given to my grandfather by his father, I have helped shoot tens of thousands of rounds through this rifle, all of my uncle's and cousin's learned to shoot with it. Still shoots as accurate today as it did when I first used it over 50 years ago.
Good theory! But I´ve got two points: 1. Isn´t friction the greatest right at the start of the rifleling, where the rifleling gets engrevated into the bullet? 2. And in addtion to your theory steel gets weaker when it is hot, so the pressure could attack easier. It seems to me that firecracking occurs earlier when a barrel gets shot often very hot....
Would love to read your thouths!
Greetings from germany
So many factors to affect, "barrel accuracy life".
heat burn out carbon in the steel