Rifle barrel burst; are cold hammer forged barrels stronger than others?

[Onty]

On another thread about lasers for bore sighting https://www.thehighroad.org/index.p...optics-helps-are-absolutely-worthless.928103/ , a gentleman posted picture what happened when laser was left in a barrel and round fired. The result is rather frightening:

That reminded me of rifle burst test in Sweden when barrel was purposely plugged pushing a bullet from muzzle side, video https://www.youtube.com/watch?v=7Jlj-sC_elM .

See discussion here https://thefiringline.com/forums/showthread.php?t=382654 . Rifles were chambered in 308 Winchester and bullet was pushed from the muzzle about 4 cm (1.57") deep.

Somewhere else I found comment that rifles that fared well were manufactured using cold hammer forging method.

I have an old sporter based on M48 action (tad shorter version of M98), with bad barrel, and considering rebarreling it. Going to see local gunsmith soon and I am thinking of going with cold hammer forged barrel blank. In my hunting areas we have snowy and muddy terrains, and in case I "manage" to plug the barrel, I would rather have one that wouldn't burst. Yeah, I know about Alaska guides' practices of taping muzzles, but considering overall cost of re-barreling, bit more for cold hammer forged barrel blank shouldn't be an issue.

 

[Insignificant bill]

On another thread about lasers for bore sighting, a gentleman posted picture what happened when laser was left in a barrel and round fired. The result is rather frightening:

That reminded me of rifle burst test in Sweden when barrel was purposely plugged pushing a bullet from muzzle side, video https://www.youtube.com/watch?v=7Jlj-sC_elM .

See discussion here https://thefiringline.com/forums/showthread.php?t=382654 . Rifles were chambered in 308 Winchester and bullet was pushed from the muzzle about 4 cm (1.57") deep.

Somewhere else I found comment that rifles that fared well were manufactured using cold hammer forged method.

I have an old sporter based on M48 action (tad shorter version of M98), with bad barrel, and considering rebarreling it. Going to see local gunsmith soon and I am thinking of going with cold hammer forged barrel blank. In my hunting areas we have snowy and muddy terrains, and in case I "manage" to plug the barrel, I would rather have one that wouldn't burst. Yeah, I know about Alaska guides' practices of taping muzzles, but considering overall cost of re-barreling, bit more for cold hammer forged barrel blank shouldn't be an issue.

Use finger cots to cover the end of the barrel

 

[edwardware]

I don't believe there's any reason to think that a hammer forged vs cut rifling barrel will survive a barrel obstruction any better. Firing a round into a barrel obstruction is not a meaningful test of barrel quality; no barrel you can buy will survive. Maybe a full bull profile barrel won't peel back as far, but I don't know what you'd gain.

If you're worried about plugging, tape the muzzle, or cover with a finger cot or condom.

 

[Show Me]

Its early but if im picking up what your laying down, who cares if the barrel splits when presented an obstruction. Would you rather the receiver blow out in your face. Lets just absolutely not let that happen. Lets hope the barrel is the week spot and the bolt lugs werent over stressed besides your face not getting blasted.

 

[sage5907]

I went through the process of getting a Bartlein barrel made and my research provided some interesting information. First, barrels that have cut rifling the steel is more stable because the heat treating and stress relieving of the steel is done before the barrel is drilled and the rifling is cut. The barrel steel is so stable that it can be threaded at the muzzle without any change in bore diameter.

I have a Winchester Classic barrel that was hammer forged. Apparently a hammer forged barrel is drilled and rifled and then heat treated and stress relieved after the rifling process. Based on what I read a hammer forged barrel when the muzzle is threaded for a suppressor or muzzle brake the bore can actually increase in diameter when the steel goes through the threading process. The steel of the bore is wanting to enlarge when worked because it was larger before the steel was hammered around a mandrel.

I have owned Douglas button rifle barrels in the past. Savage also uses button rifling to make their barrels. Apparently the steel of a button barrel is drilled and rifled and then heat treated and stress relieved after the rifling process. Based on what I read a button forged barrel when the muzzle is threaded for a suppressor or muzzle break the bore can actually shrink in diameter when the steel goes through the threading process. The steel of the bore is wanting to be smaller because it was smaller before the button was pulled through to form the rifling.

 

[mcb]

Rifle barrels are made from materials and heat treated to do exactly what happened in the OP picture. Despite the catastrophic failure of that barrel almost no fragments of any size where created.

Barrels are purposely keep only moderately hardened to produce this graceful failure. The barrel would be stronger if heat treated closer to full hard but it would also likely produce lethal fragment in an over pressure event. You can't make a barrel of usable weight survive a blockage so you make it fail gracefully/safely.

 

[3Crows]

It would make sense that with a cut rifling barrel each intersection of a land and groove would be a stress riser and point of failure. However, in normal use this is not a concern. Normal use being not plugging your barrel with mud, lasers, another bullet, cleaning rod, your pinkie etc. A hammer forged barrel would not have so sharp an intersection of land and groove and conceivably be stronger and yet it would still blow up if there was any obstruction.

Trying to shop for a rifle with a barrel that is stronger due to the type of rifling and will not blow up if obstructed is like the old 5 MPH bumpers thinking that they would reduce damage in a 60 MPH collision. Does not work that way. The forces at work with an obstructed barrel far exceed any minor differences in barrel strength due to rifling manufacture. The issue here is not the barrel but leaving something in the barrel .

 

[Onty]

Rifle barrels are made from materials and heat treated to do exactly what happened in the OP picture. Despite the catastrophic failure of that barrel almost no fragments of any size where created.

Barrels are purposely keep only moderately hardened to produce this graceful failure. The barrel would be stronger if heat treated closer to full hard but it would also likely produce lethal fragment in an over pressure event. You can't make a barrel of usable weight survive a blockage so you make it fail gracefully/safely.

I would say that barrel burst as shown in the first post is second the best to no burst at all. At least, hand/arm shouldn't be injured. Hope shooters eyes and ears are OK. A very graphic reason why to wear safety glasses and ear muffs on the range.

The bursts as shown on that video, in area where shooter usually holds rifle with another hand, is much, much worse situation. I am afraid that shooter's hand/arm will be severely injured if not completely crippled.

 

[lysanderxiii]

I have a Winchester Classic barrel that was hammer forged. Apparently a hammer forged barrel is drilled and rifled and then heat treated and stress relieved after the rifling process. Based on what I read a hammer forged barrel when the muzzle is threaded for a suppressor or muzzle brake the bore can actually increase in diameter when the steel goes through the threading process. The steel of the bore is wanting to enlarge when worked because it was larger before the steel was hammered around a mandrel.

The rotary forged barrel blank will be larger in diameter, have larger pilot hole and be significantly shorter than the finished barrel. The forging process will reduce the cross sectional area of the blank by approximately 30%. It will experience expansion during post process machining only if it is not properly stress relieved.

The same is true for button rifled barrels.

Rifle barrels are made from materials and heat treated to do exactly what happened in the OP picture. Despite the catastrophic failure of that barrel almost no fragments of any size where created.

Barrels are purposely keep only moderately hardened to produce this graceful failure. The barrel would be stronger if heat treated closer to full hard but it would also likely produce lethal fragment in an over pressure event. You can't make a barrel of usable weight survive a blockage so you make it fail gracefully/safely.

Rifle barrels can get hot even with moderate firing rates, even with bolt action rifles, It does not take much to get a barrel up to 700 -800 degrees. Therefore the temper temperature must be above this. A barrel heat treated to maximum hardness would quickly be re-tempered, and not in a controlled manner.

 

[Steel Horse Rider]

I don't want to throw water on your assertion but an 800 degree piece of steel would substantially change color. The boiling point of water at sea level is 212 degrees. Paper ignites at 451 degrees. I think 700 degrees would start a wood stock smoking pretty badly. I recommend that posts should not be made until the assertions made are checked for accuracy. I know that after emptying a few 30 round magazines through an AR that, although uncomfortable to touch, the barrels wold not ignite a piece of paper. Just saying.....

 

[Walkalong]

I'd rather have the barrel split than the action come apart.

 

[Bearcat1982]

I agree with above ... rather it split than grenade into fragments. A new barrel won't save you from a barrel bursting because of an obstruction. tape your muzzle. everyone of my hunting packs and jacket has a small amount of tape of some sort.

 

[mcb]

Example with some numbers: A common barrel steel alloy in AISI 4140. Typical heat treat for this alloy is a quench and temper process. Before quenching in oil the steel is heated hot enough a magnet no longer sticks to it, that is approximately 845°C (1550°F). The steel will be glowing moderate cherry red. It is then quenched in oil cooling it back to ambient quickly. Once quenched the steel is full hard and with 4140 that is only ~HRC 58 give or take a few points. The steel is fairly brittle at this point though not as bad as a higher carbon steel but still brittle.

The next process is to temper the steel reducing the hardness and giving the steel some toughness. Tempering is heating the steel back up but to a temperature lower than quenching. It is critical to tempering that you hold it there for an modest amount of time (a hour or two is common, shorter for thin parts, longer first thick parts) and then allowing it to come back down to ambient (you can do that fast or slow with 4140). The important part here with the temper is holding the tempering temperature for long enough for the grain structure to change. With 4140, to bring that ~HRC 58 back down to a mid HRC40's, common for gun barrels, we must reheat it to ~425°C (800°F). The hotter the tempering temperature the softer the steel will be the lower the tempering temperature the harder the steel will remain.

So to effect this temper by shooting you have to heat the barrel again to a temperature above the tempering temperature. Going lower will not have any real effect on hardness. You can certainly get a barrel hot enough to mess with its temper but you're going to have to work at it. A buddy and I playing with my thermal camera and a cheap Bushmaster Patrolman ran mags through it as fast as he could shoot and it took seven 30rd magazines to get the barrel temperature to 626°F that was the maximum temperature the camera could measure. He did 210 rds in roughly 100 seconds. From my playing with it I give the camera a +/- 25-30 degree accuracy. So to really effect the barrel temper you going to have to mag dump more than entire typical combat load of 556, to mess with the heat treat.

 

[W.E.G.]

By contrast, there is no barrel stronger than a Hi-Point 9mm pistol.

So long as the slide had room to move back, they couldn't make the barrel burst even by extreme means.

Hi-Point Pistols: The Ultimate Test MAN VS HI POINT

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youtu.be

The video cuts off, so you gotta watch a second video to find out what happened.

So what happened to that Hi Point?

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youtu.be

They finally demolished it by clamping the slide shut while firing the over-pressure round.
All the other tests were configured so as to allow the slide to "blow-back" enough that the pressure could vent somewhere.

Hi Point C9 9mm Pistol blowing up

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youtu.be

 

[lysanderxiii]

Example with some numbers: A common barrel steel alloy in AISI 4140. Typical heat treat for this alloy is a quench and temper process. Before quenching in oil the steel is heated hot enough a magnet no longer sticks to it, that is approximately 845°C (1550°F). The steel will be glowing moderate cherry red. It is then quenched in oil cooling it back to ambient quickly. Once quenched the steel is full hard and with 4140 that is only ~HRC 58 give or take a few points. The steel is fairly brittle at this point though not as bad as a higher carbon steel but still brittle.

The next process is to temper the steel reducing the hardness and giving the steel some toughness. Tempering is heating the steel back up but to a temperature lower than quenching. It is critical to tempering that you hold it there for an modest amount of time (a hour or two is common, shorter for thin parts, longer first thick parts) and then allowing it to come back down to ambient (you can do that fast or slow with 4140). The important part here with the temper is holding the tempering temperature for long enough for the grain structure to change. With 4140, to bring that ~HRC 58 back down to a mid HRC40's, common for gun barrels, we must reheat it to ~425°C (800°F). The hotter the tempering temperature the softer the steel will be the lower the tempering temperature the harder the steel will remain.

So to effect this temper by shooting you have to heat the barrel again to a temperature above the tempering temperature. Going lower will not have any real effect on hardness. You can certainly get a barrel hot enough to mess with its temper but you're going to have to work at it. A buddy and I playing with my thermal camera and a cheap Bushmaster Patrolman ran mags through it as fast as he could shoot and it took seven 30rd magazines to get the barrel temperature to 626°F that was the maximum temperature the camera could measure. He did 210 rds in roughly 100 seconds. From my playing with it I give the camera a +/- 25-30 degree accuracy. So to really effect the barrel temper you going to have to mag dump more than entire typical combat load of 556, to mess with the heat treat.

This is what I was getting at. MIL-B-11595 recommends austenitizing at 1600° F for CVM and 1575° F for 4150 with tempering at 1200° F for CMV steel and 1150° F for 4150, this results in hardness in the low 30s for these steels.

However, your numbers are just as good. If you want the steel to be harder than the mid 30s, you must temper at a lower temperature, say 400°F, if the temperature goes above 400°F the steel will get re-tempered. But, the barrel does not heat evenly, the breech end, with more mass, heats slower than the mid point, which heats the fastest, causing uneven re-tempering. This will result in internal stresses and warping.

And, even with a bolt action, you can get a wood stock smoking hot. At 10 rounds per minute, after 50 rounds, parts of the barrel can get above 400°F.

 

[mgmorden]

The result is rather frightening:

The result isn't frightening - its expected. A bore obstruction will universally cause a barrel to catastrophically fail.

 

[lysanderxiii]

By contrast, there is no barrel stronger than a Hi-Point 9mm pistol.

So long as the slide had room to move back, they couldn't make the barrel burst even by extreme means.

Hi-Point Pistols: The Ultimate Test MAN VS HI POINT

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youtu.be

The video cuts off, so you gotta watch a second video to find out what happened.

So what happened to that Hi Point?

AMAZON Store: https://amzn.to/2H7Lq6YPATREON: https://www.patreon.com/iv8888JOIN USCCA LEGAL SELF DEFENSE NETWORK: http://usccapartners.com/IV8888CHECK OUT O...

youtu.be

They finally demolished it by clamping the slide shut while firing the over-pressure round.
All the other tests were configured so as to allow the slide to "blow-back" enough that the pressure could vent somewhere.

Hi Point C9 9mm Pistol blowing up

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youtu.be

That's not totally exclusive to Hi-Points, but straight blow-backs in general.

 

[mgmorden]

So long as the slide had room to move back, they couldn't make the barrel burst even by extreme means.

You had the caveat right in your post - the Hi Point is a blow-back action. The slide is going to open up and any building pressure will release through the breech before it builds high enough to split the barrel.

With rifles, not only are the pressures involved typically a lot higher, but also many of them are manually operated which means the breech is never opening on its own unless the locking system fails. A semi-auto will have a LITTLE more wiggle room as it will eventually open on its own but its going to take a lot longer for the gas to travel down to the gas block and then open the action vs a blowback.

 

[jmorris]

No matter what you do there will be a stress riser, where there is a thick part of bore, meeting a thiner part. Same thing for where threads end.

The OP had asked me for more info on that accident but they were just photos I copied from a thread on TFL.

IIRC thats where these came from too, with a different outcome. That fellow had grabbed the wrong can of powder and tightgroup makes a horrible substitute for Varget.



Barrel looks better when pressure builds only in the thick portion before the rest lets go.



Also have photos of his mauled hand.

Makes me feel like I'm not wasting time when I double check things. Keeping photos of others misfortune hopefully reminds people I show them too, what they are dealing with.

I've had people decide they are not that interested in lathes, once they see what even a small one can do to someone, makes those rifles above look insignificant...

 

[mcb]

This is what I was getting at. MIL-B-11595 recommends austenitizing at 1600° F for CVM and 1575° F for 4150 with tempering at 1200° F for CMV steel and 1150° F for 4150, this results in hardness in the low 30s for these steels.

However, your numbers are just as good. If you want the steel to be harder than the mid 30s, you must temper at a lower temperature, say 400°F, if the temperature goes above 400°F the steel will get re-tempered. But, the barrel does not heat evenly, the breech end, with more mass, heats slower than the mid point, which heats the fastest, causing uneven re-tempering. This will result in internal stresses and warping.

And, even with a bolt action, you can get a wood stock smoking hot. At 10 rounds per minute, after 50 rounds, parts of the barrel can get above 400°F.

You have it backwards the higher the tempting temperature the softer the resulting steel. Tempering 4140 @ 400F only brings the hardness down to ~HRC 55. To get 4140 down to the mid 30's you have to go up to ~1100F. At that temperature the barrel is just starting to glow red. The only time I have seen a gun barrel taken to temperatures hot enough to glow was with belt feed abuse testing.

ETA Even normalizing 4140 where you heat it to 1600F and let it relatively slowly air cool still results it an HRC in the low 30's more that strong enough for most barrel applications though it will wear a bit faster than if it was harder.

 

[Jim Watson]

Trivia:
When Marlin introduced the .444 in 1964, they sent barrels out to Remington to be heat treated for its higher pressure vs .30-30.

 

[4v50 Gary]

Basic firearms safety rule. Both look bad.

 

[.45Coltguy]

Not knowing the entire story on this, but, it begs the question: How do you NOT know that laser sighter is NOT in the muzzle!?
You'd HAVE to know/see its there. I understand mistakes happen, but...........

 

[Jim Watson]

Back when we loaded our target rifles with false muzzles, they had a plate that blocked the line of sight so you wouldn't be prone to shooting them away. Seems like a bore sighter should be made the same way.
This type presents an unnecessary risk

 

[lysanderxiii]

You have it backwards the higher the tempting temperature the softer the resulting steel. Tempering 4140 @ 400F only brings the hardness down to ~HRC 55. To get 4140 down to the mid 30's you have to go up to ~1100F. At that temperature the barrel is just starting to glow red. The only time I have seen a gun barrel taken to temperatures hot enough to glow was with belt feed abuse testing.

ETA Even normalizing 4140 where you heat it to 1600F and let it relatively slowly air cool still results it an HRC in the low 30's more that strong enough for most barrel applications though it will wear a bit faster than if it was harder.

That's what I said, isn't it?

"If you want the steel to be harder than the mid 30s, you must temper at a lower temperature, say 400°F, if the temperature goes above 400°F the steel will get re-tempered."


Hardness, from MIL-B-11595 - Bar, Metal and Blanks, Steel (Under 2 inches in diameter) for Barrels of Small Arms Weapons:

Brinell 277 to 331 converts to HRC 29 to 36

As to barrel heating, it will depend on the profile of the barrel. For a barrel profile similar to an M14 or M16, testing has shown a sustained rate of fire of 10 rounds per minute (one round every 6 seconds) will get the thinnest part of the barrel to above 400° F after 50 rounds. 500° F would not give off enough energy to be visible unless there was little to no ambient light, and the discoloration would not show up unless the barrel was bare and polished.