hot barrel information

[markfische]

I read with great interest about hot barrels and the mechanism of failure. I realize this is just theory but Im that kind of person and would like to know. (I am a surgeon) and although that makes no difference, my mind always wanders and needs to know. I have heard about shooting too fast and shooting out the rifling (no big deal) I read about about red hot barrels and bending with accuracy loss (again no big deal) I have also read about tensile stregnth loss in the barrel because of heat and the barrel getting hot enough to fail (perforate) (bad news). Of course hot barrels cook off rounds etc. But what is the mechanism of failure in a barrel that gets too hot? Sorry I ask these stupid questions but would like to know.
I dont want theory
or guesses from some of you. I would like tested fact from someone in the industry or examples (anicdotal) my spelling is really poor. All my mind went into science and English is a far 5th.
Thanks for your time and letting me on your forum.
If I can help anyone with my limited knowledge of guns etc. I would be happy to do so.

[MistWolf]

There is a video made of a test by Colt where an M4 carbine is test fired until it failed. As I recall, the gas tube melted or burst.

In general (not ARS specifically but automatic small arms in general), barrels have been known to droop and even burst from continued firing.

I spoke to a Korean War veteran who was a gunner on a quad M2 that was mounted to a truck for anti-aircraft use. He said it was useless against jet aircraft, but he told me about using it to rake a hillside when hit by a Chinese human wave attack. He spoke of firing and firing even when the barrels got so hot, they drooped enough that he had to raise the machineguns in their mounts because the bullets were hitting low.

When steel is hot enough to glow even a dull cherry red, it has entered it's plastic state, which is between it's solid state and liquid state. Steel is heated to it's plastic state for hot forging. It's at this point when barrels start to droop and bursting starts to be a real concern

[markfische]

From what i read from you. For an M16 (or varient) the mechanism of failure is the gas tube not the barrel. Obviously bad but not as catastrophic as a barrel failure. I guess you could still loose an eye but not a hand. Thank you.
Mark

[MistWolf]

To be clear, this is one test of one specific configuration of AR. I think this was done with the M4A1 which uses the heavier SOCOM barrel profile. There is another video where they performed the same test with the M4 with the lighter profile barrel
http://www.youtube.com/watch?v=Kzfm4pYhIyY

This is also a very extreme firing schedule

[Tweak]

I don't recall the details of this picture.

http://i13.photobucket.com/albums/a264/artweaker/Troubleshooting/kBs/m4bbl.jpg

[MrSmitty]

To be clear, this is one test of one specific configuration of AR. I think this was done with the M4A1 which uses the heavier SOCOM barrel profile. There is another video where they performed the same test with the M4 with the lighter profile barrel
http://www.youtube.com/watch?v=Kzfm4pYhIyY

This is also a very extreme firing schedule

I believe the barrel blew on the M4 that they tested, well before that gas tube went on the M4A1.

[Tweak]

M4 barrel test to destruction report (https://docs.google.com/open?id=0B9ocub3kwTH8YWIzZmRkYzAtZmU0OC00Njk4LTkzYWItZWU5OTVjMTIwZTc2)

M4 barrel external temperature test (https://docs.google.com/open?id=0B9ocub3kwTH8MDBkM2JmNjktMTZlNS00ZjFiLWI5NWUtNmI4YjExNTcyZTMx)

M16A1 barrel external temperature test (https://docs.google.com/open?id=0B9ocub3kwTH8YzNkMTllY2UtZmU2NC00ZWUyLWEzOWItYmE1M2RhODViYzRm)

[Sgt_Gold]

There have been many tests, but the two most people are referencing are the test of the government profile M4 barrel, and the SOCOM profile barrel. The results were such:

The M4 Government profile is lighter under the hand guards, and thicker from the front sight block to the muzzle. The rifle was fired by loading and firing 30 round magazines on full auto until a catastrophic failure occurred. A round hung up in a red hot barrel at about 435 rounds, causing the barrel to burst. Broke gun, game over.

The SOCOM profile barrel is a heavy barrel that's the same diameter from the barrel nut all the way to the muzzle. The same criteria of firing was followed, but the SOCOM profile never reached the point of catastrophic failure. At about 900 rounds the gas tube broke, but the weapon was still operational as a bolt action rifle.

There is realistically no way for a semi auto rifle to ever reach the point of the above type of failures.

[alex71]

Interesting post. I would think the thin gas tube b would fail before the barrel would but those videos prove otherwise.

[MistWolf]

The gas tube failed with the SOCOM barrel. The M4 barrel burst due to a round stuck in the bore

[armatac]

http://www.youtube.com/watch?v=sPhbO208I2U

http://www.youtube.com/watch?feature=player_detailpage&v=XVr3lDlH6NY#t=254s

the transient nature of the heat flow means that all the cookoff/melt data is directly related to firing schedule more so than the number of rounds fired.