I went shooting yesterday, and the gentleman who treated us to a great day full of full-auto MP5 and AR15 goodness, amongst other things, accidentally shot 9mm through my .40 Beretta. He was unaware that Beretta made a full-sized .40, and it was also lying with a few other handguns in his Tahoe's trunk. So he loaded it up with 9, and shot it a bit. I had him shoot it to see whether it shot low and to the right, as it does for me.

I first noticed something was wrong when he had to chamber each round individually. As the 9 wasn't sealing in the breech, the pressure wasn't great enough to fully retract the slide, therefore causing stove-pipes and other problems. I could also make out puffs of smoke every time he fired, which is rather unusual, and the extreme lack of recoil. Don't get me wrong, this guy's SWAT, so he puts LOTS of time in in order to aclimate himself with recoil, and he's HUGE, but the gun didn't move a bit.

I thought it was just him showing his ability to control recoil, and that the jams weren't jams, but rather his large thumbs causing the slide lock to engage. So I asked him to see it, and put in a mag of .40, which I had loaded. It shot just fine. We went about our business for a minute or two, until I went back to the Beretta. I picked up the mag he had used, which he had kindly reloaded for me.

My first tip-off was the JHP. This was odd because he only had .40 in TMJ. So i popped the top round off and noticed it was 9MM!!! [SHOCKED]

He only put about 15 rounds through the gun, but how much damage could have been done, if any? I doubt much was done, but is there anything I should keep an eye on? We gathered some perfectly intact bullets after our shoot. Only a smidge of rifling was on them. Other than that, it looked like they'd been shot into water (these were FMJ). He'll never live this down!

Never tried this but the Beretta must feed the round behind the extractor. Otherwise the 9mm should have chambered and fallen right out through the barrel.  The cartridge must have been held to the bolt face by the extractor alone.

I'm wondering what those spent casings look like...

I doubt that it did any damage.

I had a couple .40 cals. sneak into my .45 magazine once.
The case burst, the bullet bounced down the barrel and of course didn't cycle the action.
The worst damage was just dirt from the burning powder, outside the chamber.

David, I belive it does. I'll have to look into it, but that would be the only way this would have happened.

Shadow,

I don't know. Once we got home, I was real upset that I didn't go down and find any of them. And I don't think I have it in me to try it again just to find out.

Anothergene,

Strange thing was that the 9mm cycled the action just enough to stove-pipe. He had to manually cycle the action for each shot. And, best of all, I collected 4 of the fired bullets. They all passed through a piece of plywood our target was handing on, and were fired from about 5-7 yards. Two are nearly undamaged, the only damage being done was that the rifling marks are not full-length. The other two hit rocks. On'e nose got bent just a bit, and the other just got scraped up and picked up some bit f the rock in the jacket. Rather interesting, I must say.

Thanks for your input, gentlemen.

I have done it too.  but with mu USPc40.  Nothing happened to it.  the casing did bulge up a bit.

I've seen this happen several times and it never resulted in pistol damage. I know a firearms instructor for a police academy that trains several agencies' personnel and when they have both glock 17 and 22's on the line it happens at lleast once every class. no ill effects to guns reported

thats pretty cool for a SHTF gun if you ever run out of .40 you can always use 9mm and at least make a couple of shots.

Shot one 9mm round in my .40 Glock.
What a funny sound.

Did the empties look like Sig 357 cases ?

Guess not .. :)  But I bet the case expanded quite a bit.