What caused this to happen?

[USGI]

I'm curious what you guys think might have happened to this shell case. I found this up in the hills the other day where a lot of locals go to shoot. I've found pieces of a revolver cylinder there before too, so that might give you an idea what can go on up there! From what I've found on the Internet, this isn't a caliber that used much in the military, so might not actually qualify as being a "Milsurp" round to most. After thinking about it a bit, I believe I know how it happened. Take a look at these pictures - I'd like to see your comments. - Bob

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[green]

Looks like a 40 fired in a 45ACP.

[USGI]

That was my guess, but would hate to have been the one firing it! Case mouth now close to the size of 45ACP and the primer strike looks offset. Ever heard of that being done before? - Bob

[CINDERS]

The primer strike would be offset due to the 40SW round sitting lower in the chamber so the Hornady logo would have been on the bottom of the chamber. There would have been a fair bit of back thrust as well after obturation before the case swelled enough to grip the chamber walls it may have been some one with a Ghost gun that cannot get 45ACP rounds but tried 40SW at point blank range a chap sitting in a car well don't matter if it wobbles down the bore it still going to do the business.
Elmer Keith in one of his stories relates to how one of his friends was kept a prisoner by a cowboy who took all his rounds (45Colt) but let him keep his HG the lad one day found a smaller cal bullet wrapped the hull in paper till it could just be driven flush into the chamber when the chance arrived the young chap shot & killed the cowboy at close range, even though the round would have wobbled down the bore it did the business.

[WarPig1976]

Ever heard of that being done before?

Yes, there's videos on Censortube of people shooting the wrong caliber on purpose. Every once in a while I'll find a batch at the club somebody shot accidentally.

[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...

[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.