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

[lysanderxiii]

For an M16, the M14 temperature graph is similar.

 

[Walkalong]

Makes me feel like I'm not wasting time when I double check things.

Amen to that!

 

[mcb]

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.

400 or 500 F will not effect a gun barrel made from properly heat treated 4140 or 4150. Your chart says you have to temper 4150 to 1150 degree to get your hardness down to 29-36 . To make that steel even softer/weaker later you would have to heat it hotter than the original tempering temperature. To make it harder you have to go all the way back to the quench process (heat to austenitizing temperature and quench). Can you hurt a gun barrel getting it hot, yes. But you have to get it really really hot (above the original tempering temperature) and in most cases few of us are going to shoot it enough to get there. 1150F would be visibly glowing red in most lighting conditions except maybe bright sunlight.

 

[Show Me]

I was early to this ,now I'm late. Sure has taken a turn. Junior high school metallurgy. We made screw drivers and cold chisels. Why would anyone think pizza cooking temp will affect steel barrels. I must have got left behind .

 

[Show Me]

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.

View attachment 1196584

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

View attachment 1196585

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...

Good picture show and tell !!!!

 

[rust collector]

This is fascinating. The OP related to pros and cons of cold hammer forged barrels, however, as they relate to an obstructed barrel. As I understand it, CHF barrels are generally tougher, but that likely translates only to a different fracture pattern when subjected to an obstructed bore overpressure. They all will fracture.

All barrels are compromises. The manufacturer balances material cost, production cost, tensile strength, corrosion resistance, machining characteristics and a host of other factors in designing and producing barrels. When one aspect is improved in some way, other aspects generally suffer.

As with the delicious variety of apple, which was changed over the years not to make it more delicious, but to make it less subject to bruising and longer lasting on grocers' shelves (all at the expense of taste and texture), a manufacturer's choice to invest in hammer forging is made for the benefit of the manufacturer. The price paid for that toughness is higher cost to amortize the necessary machinery, change in other steel attributes to accommodate the process, and accuracy. Because of the big investment producers must make, the little guys are squeezed out of some markets and the big guys do a lot of chest thumping to sell more barrels.

I am no metallurgist. Here's a link to a discussion of the various production options, pros and cons:
https://www.americanrifleman.org/content/popular-rifling-types-advantages-disadvantages/

 

[Jim Watson]

I have not before heard of "Cation" rifling; it describes the grooves as acid etched into the bore.

The article does not mention ECM (Electro-Chemical Machining) for rifling, which I think S&W uses for their Monster Magnums and Nowlin used for 1911 barrels.

 

[RainDodger]

Regarding the first post with the picture of the mangled laser bore sighter... I'm a range officer and one day while walking the range at about 75 yards out from the firing line, I found a similar bore sighter that had been launched from the firing line. It was slightly mangled but not to the extent of the one in the picture. It definitely was beyond repair however! It must not have fit the bore very tightly, otherwise there likely would have been a barrel failure. When I see shooters on the range using a muzzle-mounted device, I always watch them until they're finished. I'm a proponent of doing your bore sighting at home, just to prevent crap like that.

 

[lysanderxiii]

400 or 500 F will not effect a gun barrel made from properly heat treated 4140 or 4150. Your chart says you have to temper 4150 to 1150 degree to get your hardness down to 29-36 . To make that steel even softer/weaker later you would have to heat it hotter than the original tempering temperature. To make it harder you have to go all the way back to the quench process (heat to austenitizing temperature and quench). Can you hurt a gun barrel getting it hot, yes. But you have to get it really really hot (above the original tempering temperature) and in most cases few of us are going to shoot it enough to get there. 1150F would be visibly glowing red in most lighting conditions except maybe bright sunlight.

You are entirely missing what I am stating.

I am not saying the 500° F will hurt a normal barrel, I am saying that it would hurt a barrel hardened to HRc 45 - 50 or higher.

If you make a barrel the normal way, everything is fine, you will never re-temper the barrel.

The reason barrel are tempered to the hardness they are is because if you tried to make it harder you will have to lower temper temperature, and run the risk I noted.

 

[Show Me]

You are entirely missing what I am stating.

I am not saying the 500° F will hurt a normal barrel, I am saying that it would hurt a barrel hardened to HRc 45 - 50 or higher.

If you make a barrel the normal way, everything is fine, you will never re-temper the barrel.

The reason barrel are tempered to the hardness they are is because if you tried to make it harder you will have to lower temper temperature, and run the risk I noted.

Personally I missed it and this is interesting. More advanced than a seasoned machinery mechanics pay grade

 

[mcb]

You are entirely missing what I am stating.

I am not saying the 500° F will hurt a normal barrel, I am saying that it would hurt a barrel hardened to HRc 45 - 50 or higher.

If you make a barrel the normal way, everything is fine, you will never re-temper the barrel.

The reason barrel are tempered to the hardness they are is because if you tried to make it harder you will have to lower temper temperature, and run the risk I noted.

Ah I understand and I don't disagree but I believe the primary reason they are tempered that soft is for safety and allowing them to fail gracefully as in the original post.

The tolerance to thermal cycling is bonus.

 

[Walkalong]

allowing them to fail gracefully as in the original post.

Amen to that.

 

[DM~]

Bottom line is you can't fix stupid!

DM