What caused this to happen?

[browningautorifle]

That's right, fired in a .45 chamber. The bullet comes out just fine...you can tell something happened by the sound too. Not dangerous to the firer though. I've seen enough of this over time, never done it myself. The use of a 7.62 in a 30 cal chamber leaves you a long straight case looking like a .444 Marlin rimless or a very long .44 automag...

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[Ovidio]

There is a video also from demolition ranch or something like this where he tries things like these.
The shells get ruptured or bulged, but there is normally no overpressure.

[Patrick Chadwick]

Note that in the last photo of the series, the initial strike was close to the H of Hornady (in the headstamp). The case, expanding asymmetrically, pushed the base up, thus dragging the striker across the fired primer to the 0 of the 40 S&W headstamp. That is what caused the vertical lengthening of the striker indentation.

[USGI]

I'm aware of other "wrong" caliber ammo being fired in guns before, and should've been more specific that I meant the .40 S&W only. In this case, I thought it might not even fire since a .40 case is about .050" shorter than a 45 ACP. Also, wonder what kept the whole round from just dropping completely through the barrel? Maybe the weight of the bullet helped it to "catch" at the bottom on the front end of the chamber? Would it be possible for a .40 to be fed from the magazine if mixed in with the .45 rounds? It could've been a practical Joke by a shooting buddy who loaded his mags? It seems like the firing pin would've had trouble reaching the primer, too. It's a bit hard to tell from the pictures, but there's no expansion on the side of case where it was in contact with the bottom of the chamber. It's completely flat on that side - since it was already in contact, the expanding gases didn't affect it any. - Bob

[browningautorifle]

Fed from the mag or an open gun, the extractor would catch and hold it against the breech face. This looks like a Glock firing pin strike to me, thus long like a Bren gun.

[USGI]

I just looked at some good cases (45 ACP) that I picked up in the same spot that day. They all have small "bright" areas to both sides of the firing pin strikes. A couple of those cases were nickel plated Hornady and have about the same amount of tarnishing on them - been there on the ground awhile. Do you think a 1911 .45 extractor would "catch" and hold on a .40 case like you described? Thanks! - Bob

[browningautorifle]

Do you think a 1911 .45 extractor would "catch" and hold on a .40 case like you described?

I just tried with my Auto Ord and the .40 fit and fed perfectly out of the mag. When I released the slide the cartridge was launched out of the barrel. Then I carefully tucked it in under the extractor and it stayed. It might work, it would when held vertically, I still wonder if that was a Glock that did that? Mine is a 22 so I can't try it. I'd need a 21...

[CINDERS]

Now thats a real bizarre one Skip...

[Bruce_in_Oz]

Another one is "9mm confusion".

Saw an interesting example of that the other day. A 9 x 21 case that was sporting a "belt". Other clue was the faint parallel lines along the case.

Best bet: Somebody with an MP5 got hold of the wrong ammo and gave it a whirl in the "work gun".

Theoretically, it shouldn't fire "out of battery", however.....

[browningautorifle]

I know a man that collects those too...