Why did this happen?

but then again so is the fact that your garand did it, so crazy things do happen. does the tang on your m1's firing pin still look geometrically correct? and the slot in the rear of the bolt where it goes? thats as strange as the op's deal

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The Garand in issue had just come back from the Gunsmith completely matched out, including a new Barnett match barrel.

Zeroing it in, for the first time, it slamfired from the clip. Rounds were handloads with federal primers. I had reamed the primer pockets and inserted all the primers by hand, so I know that there were no high primers. But the gunsmith said that the cases were a little tight and a little long. "Conventional" said that only high primers caused slamfires. I found out that conventional wisdom is all bunk.

The gunsmith has the receiver. My little out of battery slamfire blew the back off that Garand receiver, so no one is measuring firing pin tang.

I believe that the "conventional wisdom" that AR's cannot slamfire out of battery is bunk. I can't find my copy right now, but my recollection is that in the book "the Black Rifle" the Army had to redesign the M16 firing pin not just because of slamfires, but because they also had out of battery slamfires.

This may be the first internet report of one.

Which is why everyone is looking at the thing and scratching their heads. "It can't be", "it's impossible", etc, etc.

Incidentally, Garand slamfires leave nice primer dents. They don't look any different from normal.

I'll avoid the usual lengthy explanation and suggest it was a late ignition by a significant portion of the powder during extraction. It fits all the known facts of the situation, and is probable given the ammo manufacturer's reputation.

It didn't fire out of battery, it finished burning out of battery.

A cheap set of calipers would be nice, measuring the portion just ahead of the bulge would reveal how close it is to the diameter at the rear of the chamber. That's the only place it could stick, given the bulge is larger, and was likely hanging out.

It would help to confirm the bolt was partially open during the attempt to remove the casing. Was that specifically mentioned yet?

...but to be honest the most likely explanation is that it was fired in a rifle chambered for .30cal (or thereabouts) by mistake.

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The OP says he took it out of his rifle which is a 5.56 stag arms

Shooting dirty ammo leaves crud, crap, and what not in the chamber.

Some of that crud and crap does manage to get into the firing pin hole in the bolt.

Pull the trigger, bang, pin sticks forward, extracts spent round, starts to feed next round, we have been told the chamber was having problems, STUCK pin hits primer, OOB

For every reason somebody will give, someone will say "no way"

Fact is, anything is possible, something went wrong, only the OP has possession of the upper, it needs to be cleaned and inspected by a gunsmith before using again

I am having a hard time comprehending how this happened.

What I understand from the OP:

1. The round was fired in a 5.56 chamber.
2. The round was not fired while out of battery.
3. The chamber did not explode or deform.
4. The case failed to extract from the chamber.
5. The OP extracted the case with a rod and by pogo-ing the rifle

This means that the round was not oversized while in the chamber, but was restrained while in the chamber and then somehow ballooned out to the pictured state after it was removed from the rifle.

I can't understand how steel could behave this way....a real mystery, or I have misunderstood the facts.

Bob

If the bolt carrier is within spec then it did not fire out of battery. I've had reloads that were not full length resized cause the rifle not to fully go into battery and the hammer will hit the bottom of the bolt carrier but not the firing pin.

I would inspect the lugs on the bolt itself for any damage. Also the lugs of the chamber to be sure it is locking while in battery. Also inspect the cam pin to see that the bolt is not obstructed in its rotation.

I am at a complete loss for how this can happen but I am really curious.
It could not be OOB since he had to remove the casing himself and since it is almost impossible for an AR to fire OOB.

The primer looks wrong. The hole looks to deep and way to wide for an AR Firing pin.


I think I am gonna post a link to this over on M4 and get their input.

I know I would not fire the gun or any more of the ammo till I was 100% sure what happened.

I'll avoid the usual lengthy explanation and suggest it was a late ignition by a significant portion of the powder during extraction. It fits all the known facts of the situation, and is probable given the ammo manufacturer's reputation.

It didn't fire out of battery, it finished burning out of battery.

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I think you're probably correct.

For all of the people who are suggesting an out of battery explanation, didn't the OP state that the round was stuck IN THE CHAMBER and he had to beat it out with a rod and pogo-ing the rifle?

I really hope that if the case was really stuck with 2/3 or more hanging out of the chamber that the OP would have mentioned it.

Bob

nofishbob-

There is NO WAY that case would be distorted in that fashion if it had been completely inside the rifle chamber during combustion unless it was in a chamber cut for a larger diameter case

MistWolf-

That is why I am befuddled by this.

If it was in the chamber, the case could not deform like this without the chamber being destroyed.

If it was stuck significantly out of the chamber (Like by 2/3), why did the OP not tell us?

All of the "Unexplainable" technical mysteries that I have been involved with were eventually solved, not by the discovery of a new property of physics or chemistry , but by the correction of a mistaken assumption made early in the process.

Bob

I woke up in intensive care after an accident and a couple operations and they had put a kidney machine connection in my wrist.
I told them I needed to take a leak, and they gave me a urinal.
So the next day they operated on my wrist and took out the tubes.
While the surgeon was operating on me, I asked "Why did they put tubes in my wrist?"
The surgeon replied, "I will have to speak to the other surgeon. Interesting case."

kanook said:

The OP says he took it out of his rifle which is a 5.56 stag arms

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True, so it is one of the other half dozen possible situations...or a case of mistaken identity (with the case). It is difficult to know for certain without more information, but I am going with the cartridge being fired before the bolt was completely locked. If it were completely unlocked it would be darn near impossible, result in significant damage to the rifle and most likely the shooter as well as destroy the case (in its entirety, not just a small fissure).

The primer looks wrong. The hole looks to deep and way to wide for an AR Firing pin.

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+1, and that lends credit to the "something stuck in firing pin channel" theory.

From the evidence, I strongly suspect THAT case was fired in a 7.62x39 chamber. Look at the taper of the bulged section. Look at the diameter of the case mouth and the stepped part behind it.

When you extracted the stuck case, where did you find it? I'd bet it was on the ground amid other spent casings. I think the wrong case was picked up and this one did not come from your rifle. The primer shows sever indentation, indicative of being struck several times by a firing pin. I have used many a spent case in dry firing and in each case, the primer ends up looking just like this one. My suspicions are that whoever had to extract this case from their chamber let the hammer fall on it a few times

I've gotta ask the OP...Do you own a .308 AR?

From the evidence, I strongly suspect THAT case was fired in a 7.62x39 chamber.

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Ding, ding, ding!!!

We have:
1) A case that does not fit in a 5.56 chamber.
2) A case that if unsupported when fired would have completely ruptured, not bulged.
3) A rifle that is very hard to get to slamfire.
4) A rifle that only unlocks after the bullet has left the bore and pressure has started falling rapidly.
5) A picture of what looks exactly like a 5.56 case that's been fired in a 7.62 caliber rifle.

Whatever else the OP says, the facts as presented point directly to that 5.56 case having been fired in a 7.62 cal rifle.

BSW

It didn't fire out of battery, it finished burning out of battery.

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Hard to believe. Given the difference in burn time, cycle time, pressure drop, I would like to see some analysis on how this could happen.

Whatever else the OP says, the facts as presented point directly to that 5.56 case having been fired in a 7.62 cal rifle.

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That is certainly in conflict with the OP's statement of:

I own a Stag Model 2 and Colt 6920. The only other rifle on the range that day was a Mosin. I do not own a gun chambered for 7.62x39.

I am 100% absolutely, positively, unequivocally certain that the round is a .223 REM fired out of my 5.56 chambered Stag Model 2..

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Can a .223 be chambered in a 7.62 X 39? Heck if I know.

Looking at the neck and body, I wonder how the case compares to 6.8 spc and 7.62 x 39.

Not that anyone would ever chamber a 223 round in one of these...

Since we have ruled these two possibilities out, I suspect a slam fire while chambering the round. Look at the case diameter before and after the bulge, and the case neck.

From the evidence, I strongly suspect THAT case was fired in a 7.62x39 chamber.

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For the record, I said the same thing two pages ago, post 21. Again, no offense intended to the OP, but no other explanation works. Perhaps it was on the ground already when you picked up the one you dislodged?

Does this photo look familiar? Yes, .223 ammo will chamber and fire in a 7.62x39 chamber. The primer dent even looks the same.

Can a .223 be chambered in a 7.62 X 39?

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Yes, and it will fire too.

I've seen it done by a guy that mixed a 5.56 round in with his 7.62x39. A friend was helping him stuff mags and neither of them caught it before it was chambered and fired. It made a weird 'pop' sound and, amazingly enough, the bullet hit the target. BSW

Wow, fatelk, that is some really compelling photographic evidence!

Bob

I'll avoid the usual lengthy explanation and suggest it was a late ignition by a significant portion of the powder during extraction. It fits all the known facts of the situation, and is probable given the ammo manufacturer's reputation.

It didn't fire out of battery, it finished burning out of battery

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I've never even heard of this happening but seems that this is the most likely scenario IF in fact this wasn't from a 7.62 x 39 rifle. My money is with fatelk's explanation.

In any case, get a gunsmith to look at your rifle.

Does this photo look familiar? Yes, .223 ammo will chamber and fire in a 7.62x39 chamber. The primer dent even looks the same.

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Fatelk: That picture is very close to the OP's case. I think it more likely that the OP's picture is that of a 223 case fired in a 762 X 39 chamber.

Only AR15 slamfires that I have had (!) or seen, have been in battery. I would still like to see a case from an out of battery slamfire in a AR15.

I guess it will be a while.

General consensus on M4 is the same. This was fired in a 7.62x39 chamber. If there was no 7.62x39 gun around then the only explanation is that someone else fired the round before hand and the case was on the ground near where the casing from the the OPs rifle fell.