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Looks like OOB detonation.
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No, it doesn't. Not even close. Please explain how this could be an OOB, and explain how an OOB even happens in the AR-15.
I'll give the same response from the last thread:
OOB = unicorn myth that keeps getting regurgitated. Plus the extractor is clearly blown out which does not happen in an OOB.
The is classic case failure.
What cause the case failure is either overpressure (most common) or bad brass.
This was clearly overpressure, due to the blown out and pierced primer. If the brass was the only failure you would not see those. OOB does not flow brass into the ejector well, nor does it blow out at the extractor like this, that happens with a locked chamber only.
So we have overpressure.
Overpressure in an otherwise well functioning rifle can be caused by barrel obstruction, wrong caliber ammo (300 BO in a 5.56 chamber), wrong powder, or powder overcharge. In theory bullet setback as well but that's more theoretical than practical in 5.56 rifle cartridges.
Barrel is not currently obstructed.
If this was 300 BO the barrel would be obstructed.
It is *possible* the barrel was obstructed, and this round being fired cleared both bullets. This means the previous round would have had to have been a squib, and the shooter would have had to cycle the action manually, or would have heard and felt all the gasses being vented backwards instead of out the muzzle as well. You are getting into some unicorn farting fairy stuff if you think the bullet stopped in between the gas port and the muzzle, cycled the action, and the second round kaboomed into it. Even if that did happen this would have not resulted, AND there would be severe barrel damage where the bullets collided.
Wrong powder in a single round of commercially produced ammo doesn't really happen. (Assuming this is actually Winchester ammo and not someone's reloads using Winchester cases.
It's also possible, since the rounds were not inspected prior to loading the magazine by the shooter, that this ammo had a visual defect, like extreme setback, however unlikely.
Most likely candidate = overcharge. Bad ammo.