Out of battery kabang.

[26 Inf]

Apologies in advance, I don't have pictures because they said no copies. I have not handled the parts and pieces.

Case head blew out, in front of case head there is about a 1/8 wide ring of expanded metal around the circumference of the case, to me this indicates how far the case was out of battery when it fired.

Shooter had shot 5 mags, of 8 available, before mishap. When policing brass one piece was found near the shooter's firing point with no primer in the primer pocket. Likely, but not certain it came from shooter's rifle.

Bolt carrier was cracked on the sides and bent slightly downward near the bottom. Remarkably, at least to me the bolt seemed to be intact. The firing pin also appeared to be normal and intact (no measurements provided). The extractor was bent significantly outward and the case head from that area of the case was missing. There was significant flow around the ejector which helped locate the case's orientation. Bore of weapon was clear.

Shooter had shot 5 mags, of 8 available, before mishap. When policing brass one piece was found near the shooter's firing point with no primer in the primer pocket. Likely, but not certain it came from shooter's rifle. I was told FCG function-tested OK and there was no sign of primer in lower.

Any ideas as to what could cause such an outcome?

[markm]

Out of battery is nearly impossible with an in spec AR. Without the bolt lugs rotated, you don't have the pressure to yield a Kabizzle. These are almost always case failure due to excessive pressure... and this is generally due to an over charge of propellant.

[vicious_cb]

Out of battery is nearly impossible with an in spec AR. Without the bolt lugs rotated, you don't have the pressure to yield a Kabizzle. These are almost always case failure due to excessive pressure... and this is generally due to an over charge of propellant.

Yep, the hammer can't even strike the firing pin until the BCG is in battery. Nor does the firing pin carry enough inertia to ignite a primer on its own.

[Thrasos]

What kind of ammo was he/she firing? I agree that modern ARs that are built to spec should not fire OOB, but if you're firing junk ammo with soft primers, you could shoot OOB if you suffered a double feed.

[georgeib]

Is it possible that debris in the firing pin channel could have caused the pin to stick and protrude from the bolt face and ignited the primer prematurely?

[Thrasos]

Another thought...how old was the weapon? I vaguely remember that older weapons that were assembled without a cam pin would allow firing without the bolt rotating --which could spell disaster.

[Clint]

Is it possible that debris in the firing pin channel could have caused the pin to stick and protrude from the bolt face and ignited the primer prematurely?

The AR has positive firing pin retraction, so it really can't stick.

Another thought...how old was the weapon? I vaguely remember that older weapons that were assembled without a cam pin would allow firing without the bolt rotating --which could spell disaster.

It's bad juju to assemble and fire any AR without a cam pin.

[Clint]

Out of battery is nearly impossible with an in spec AR. Without the bolt lugs rotated, you don't have the pressure to yield a Kabizzle. These are almost always case failure due to excessive pressure... and this is generally due to an over charge of propellant.

This.

Too much pressure from a wrong powder charge or excessively soft brass.

[26 Inf]

Out of battery is nearly impossible with an in spec AR. Without the bolt lugs rotated, you don't have the pressure to yield a Kabizzle. These are almost always case failure due to excessive pressure... and this is generally due to an over charge of propellant.

Yep, the hammer can't even strike the firing pin until the BCG is in battery. Nor does the firing pin carry enough inertia to ignite a primer on its own.

That is why I asked, same thoughts.

I'm aware that the firing pin isn't long enough to protrude beyond the bolt face until the bolt carrier and bolt are compressed (for lack of a better term).

Also understand the mechanics of the hammer following the bolt home.

The things than give me pause:

1) The ridge/ring of expanded brass indicates the case expanded to the dimensions of the chamber as it was slightly out of battery, before the case head separated. I'm not describing this very well, think of what happens when you fire a 9mm in a .40 - the case expands to fit the chamber - that's what this looked like except before the case head.

2) I also noticed what I called unusual brass smears on the upper portion of the ring of steel surrounding the bolt face and on the extractor itself - from about 7 to 11 o'clock. These weren't from chambering IMO and indicated to me the round fired before the base had contacted the breech face of the bolt.

I'm wondering if there is any possibility that a primer somehow stuck to the breech face and set off the round being fed as the bolt tried to close.

What kind of ammo was he/she firing? I agree that modern ARs that are built to spec should not fire OOB, but if you're firing junk ammo with soft primers, you could shoot OOB if you suffered a double feed.

This was new ammo fired during an agency training session. However, manufacturing is manufacturing and a touchy primer can happen.

I guess we will never know for sure.

[MistWolf]

If the barrel the chamber is cut short in the barrel and the barrel extension head spaced to that, there will be more unsupported area of the case. Symptoms include pressure rings around the web and cases expanding enough that the primer will fall out.