How would this happen?

[SG500]

Attached are some photos of a case that is bulged towards the top of the case.
How could this happen?
Surely it wouldn't happen in a barrel and presumably if a round cooked off in a box of ammo it would crack the case - this case isn't cracked at all.
Dave.

 

[hicky1300]

Hi SG
Interesting one. I think it has `cooked off` just not what I`m used to seeing. I had a load of WW2 .50`s from a crashed Typhoon & all these had obvious scorching to the case & blown out primer but the bullets had stayed crimped in.
This does not look as though it has got as hot but the redundant primer housing does look like it has fired and the later .50`s were crimped differently to the earlier ones - particularly Kynoch`s.

 

[Fuzeman]

Hi Dave thats interesting , in 1970 whilst in the TA we were treated to a demonstration of what happens when you fire a full mag into a box of ammo, the result was those that Went off just had split cases, none pierced the outer packaging, i never saw one bulge like that.

 

[US-Subs]

I've seen it sometimes in the past where if it is a thin case, deterioration of the propellant - from heat, moisture, etc - can cause release of gases and result in hi-pressure. We see a similar effect sometimes on chemical rounds where deterioration of some chemicals creates enough pressure that it shears the threads and forces the adapters off the body. This is most common on Japanese munitions containing DA/DC.

 

[tc464]

I've seen it sometimes in the past where if it is a thin case, deterioration of the propellant - from heat, moisture, etc - can cause release of gases and result in hi-pressure. We see a similar effect sometimes on chemical rounds where deterioration of some chemicals creates enough pressure that it shears the threads and forces the adapters off the body. This is most common on Japanese munitions containing DA/DC.

What he said. I've seen the bulging due to propellant deterioration in magazines that are poorly maintained, especially in Africa and South America. I haven't seen it in individual small arms rounds, but I've seen it in cases of small arms ammo before, especially Russian stuff. Another nasty problem with this is that it releases hydrogen, and it is the most popular explanation for storage accidents that cannot be explained otherwise.