Colt Expanse Kaboom

[VanceMMA]

Is it possible that something broke around the cam pin area causing the bolt to not rotate and fully chamber a round but the carrier closed anyway? That might explain the failure before the kaboom.

[Todd.K]

There sure are a lot of wild ideas being thrown around but no evidence pointed to. I've done my best to point out a few facts about the interaction of the bolt, carrier, and firing pin in relation to the possibility of an OOB. Details anyone reading this can try for themselves if you own an AR.

I'd like to clear that the make is no interest to me. My conclusions are based on what I see and what I know of the system. Please back up the "not real Colt" talk with a specific "not real Colt" part you think failed and caused the kb.

I don't see any failed parts that could have caused this.

I do see signs of excess pressure on the case.

[Todd.K]

Is it possible that something broke around the cam pin area causing the bolt to not rotate and fully chamber a round but the carrier closed anyway? That might explain the failure before the kaboom.

The carrier would need to be split open far enough that the cam pin was not turned over to locked. I don't see how the carrier is able to slide in the upper if it's split that wide.

[Todd.K]

Case head 3 Note the imprint of the ejector.

Brass doesn't flow into the ejector hole like that at normal pressure.

If the bolt isn't locked why is brass flowing into the ejector hole? It would just push the whole bolt to the rear.

[Iraqgunz]

Thank you!

I'm sorry but you have no idea what you are talking about.

This was not an OOB.

[Iraqgunz]

I have seen several kabooms, to include my SBR two years ago. The root cause was ammo and the company acknowledged it. The bolt was whole, with exception the extractor which was bent backwards. The carrier was also split.

I have another one I just picked up (S&W MP-15) which the entire rim of the casing was blown out and the casing is stuck in the chamber. That bolt is also whole with exception of the extractor.

The AR design as mentioned by Todd.K cannot fire out of battery as the firing pin cannot protrude through the bolt face. The exception would be a bolt in which the firing pin hole is elongated or otherwise out of spec, which is why the military has a gage for that check. That would allow the firing pin to penetrate deeper and also pierce the primer.

I do not concur. A protruding firing pin (which can occur with a dirty weapon) can ignite the primer before the bolt locks. The locking lugs also show no signs of damage - not in the slightest. If there was a high enough chamber pressure to cause that level of damage, the lugs would generally show some signs of distress. The pressure that did that damage can be 50 kpsi combustion gases that exited from the ruptured case. If the bolt/case/chamber do not restrain gas pressure, the rest of the mechanism will most certainly be severely damaged - as seem in the photos.

[JC5188]

Do these, among the first pics of the rifle, not remove an OOB event as the cause of the KB?



I'm no expert, but it seems an OOB would not see the bolt return to lockup, given that the carrier was destroyed. Is that correct?


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[lysander]

I'm no expert, but it seems an OOB would not see the bolt return to lockup, given that the carrier was destroyed. Is that correct?


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Logic would tell us that an out-of-battery discharge of the cartridge would not have the bolt locked into the extension afterwards.

You don't have to be a expert to come to that conclusion.

[rickgman]

Todd, I'm not sure I understand what you are asking. The photo is of a separated case head not the ejector hole in a bolt face. The ejector impression in the case head can definitely be indicative of overpressure but it also can be due to other things - like impact with the bolt face when separation occurred.

However, that aside, let's go back to what we do know. Firstly, Federal found no issues with excessive chamber pressure when testing other ammo from the same box. That's a big clue to me. These are real measurements (not supposition) and tend to discount a systemic overpressure issue with this lot of ammo. I use to have a boss who often said "I'll stack my one piece of data against all of your theories". That doesn't mean that this single cartridge didn't have an issue but ammo manufactured using a commercial process do tend to be somewhat uniform. Secondly, this damage was far worse than any I've seen before that was attributed to bad ammo. This is far worse than a simple cracked bolt and carrier. I will concede that Federal 5.56mm ammo doesn't have a great reputation. Thirdly, there are signs when looking at the forward portion of the failed case that indicate that the case was unsupported by the chamber when the failure occurred. That can be due to an out of battery ignition or from premature unlocking of the bolt. Premature unlocking (while the chamber pressure is still near the max level) can be due to excessively high pressure in the gas system. If this was a short barreled AR type rifle, I'd be more likely to favor the latter but it was a 16" barrel.

The long and short of this situation is that there is no conclusive evidence to say exactly what did happen. The various parts are severely damaged and it is virtually impossible to make detailed examination of the failed parts using photographs alone. If you feel more comfortable attributing the failure to ammo, that's fine. I'm not so sure and think that I'd favor Federal's conclusion.

[rick10mm]

Wouldn't the manufacturer want all these parts back to examine ??