This happened a little while ago and we’re all stumped. The rifle fired 7 mags without malfunction before this happened. My buddy fired half a mag, ran, turned and fired. It fired once, but the second shot caused this. The first shot didn’t sound different at all.
It was about 100 degrees that day, we were running around dunes so there was lots of sand, but we all have excellent weapons discipline when it comes to where we put our barrels. The ammunition was standard military.
In case you’re wondering, he’s fine, just a few lacerations in the hand.
any help would be appreciated.
My guess would be that you had a round cook off with the bolt not locked into the barrel extension.
Edited to add: Which ammunition exactly was it? At what rate did you run the seven mags through the weapon?
Looks like the lower survived. Good thing since it looks like Class III.
Just your standard green tip, lake city, 5.56.
We were shooting pretty slowly, about a mag per minute, but about a minute or so break in fire after about 2 mags.
Im no expert by any means so take this with a grain of salt, but did the first round stick in the bore??
Ive never had a big boom, knock on wood.
Sorry about your buddy.
Well, it looks like a round went off while the bolt was not properly locked into the barrel extension. Were you able to recover the suspect case? Another possibility is a slam-fire due to a high primer, however that would be unlikely with M855 - but not impossible.
That would have causes a bulged/ruptured barrel.
foreignadvisor, what does that barrel look like under the HG?
It fired out of battery somehow meaning cookoff or some other way or had excessive headspace As anyone knows who has ever reloaded .223Rem/5.56mm knows you can’t double charge the case, the power spills out of it and you can’t seat a bullet.
looks awful dry, though I wouldn’t think a lack of lube would do that.
It won’t.
Unfortunately we weren’t able to extract the case, we weren’t even able to break the weapon down for evacuation. The way you see it, that whole mess, is locked together like one big piece of abstract art. Not even slamming it on concrete could get it unstuck.
There wasn’t any bulging under the heat guard either. Nothing seriously wrong with the barrel.
I don’t think it was a cook off…
It must have been a squib before the kill round, because the bolt is still locked into the trunnion.
Think about it…
- Round is fired, bullet traveling down the barrel
- bullet hits the other bullet stuck in barrel and pushes it beyond the gas port
- gas travels to inside of carrier for unlocking
- BUT…carrier can’t rotate the bolt becuase of insane pressure inside barrel
- Result, carrier splits side ways and explodes the receiver and mag.
The crack near the barrel extension is telling. My opinion is that this did not happen on the “second shot”. I believe there wasn’t even a “first shot”, this happened when a round was on it’s way into battery. Hammer is locked back and gun is on safe. 
the hammer was probably blown back by the boom, and the selector is probably on safe from good training
the squib question could be further investigated with a bore light- that’s the first thing i’d look for. if there’s a bullet down there, there’s probably two of them. the bolt does appear to be locked, but the firing pin is still pretty much where it should be- if the powder charge backed in through the bolt, causing that kind of train wreck, i’d expect to see the firing pin lodged in the buffer- at least not where it is.
i think the katar probably has the best theory, and the bolt is where it is because thats where it landed, not because it’s locked.
do you suppose some kind of double feed? is it possible he had a FTE and the next cartidge somehow detonated loose? first round cooked before engaged, blows carrier back leaving cartridge in the chamber, carrier comes back, picks up second round, which cooks off in the action? seems far fetched, but it looks like someone threw a stick of dynamite in there
At first glance it looks like the bolt is locked however the cam pin hole appears to be strait up/down. If the bolt were locked then the cam pin hole would be offset. Some how I think it must have fired out of battery.
I think I am going with Katar on this. Can we assume that this is a privately owned weapon or is it issue? If it is private then I would leave the weapon as is and contact Colt. I would email them pics as well. I have a contact there if you need it. If it was military I would do the same so that a proper investigation can be done. I would also attempt to identify the exact lot # of ammuntion used and would segregate and tag it. This will be helpful in the even that it was ammunition related. I have done a couple of explosive/ weapon mishap investigations and it is very important to leave the weapon in its’ current state to help find the problem.
Yep, out of battery. Possible that the firing pin could have gotten stuck forward and the round fired on it’s way from the magazine to the chamber?
We had a customer years ago that shot himself in the hand with a Beretta .25 (or .380) that he dropped the slide on. Years of carry and neglect of the firing pin channel meant that pocket lint and other junk had accumulated and locked the firing pin in the forward position. The gun was virtually undamaged but his hand was good and chewed up.
Possible that the firing pin could have gotten stuck forward and the round fired on it’s way from the magazine to the chamber?
Even if the FP gets stuck forward it’s impossible for it to touch a primer until the bolt is locked into battery. The Firing pin can’t protrude through the bolt face unless the bolt is fully rotated into the extension.
Good point.
I think I am going to revise my initial thoughts and say that something ammunition related happened here. This is why it is extremely important to know what lot # the ammunition was. One could then check it against NAR’s that are in effect for particular types and lot#'s of ammunition to see if problems were previously reported.