9mm in a .40...

[Parrothead]

I almost had a issue at the range last week. I took a new shooter out for some practice. I stayed within a few feet of him for the first hour or so. At that point, i thought he had a handle on loading, firing and clearing the weapon. I had him shooting my G19 for simplicity and he handled it well. However, i took a moment to shoot and then looked back over at him. At that time, he was loading 9mm ammo into my Sig 229 (40). I was a little surprised the round fit in the magazine so easily. Anyway, i was able to fix the problem before he loaded the weapon.

So here's my question; What would have happened to the firearm had he successfully fired the 9mm in the .40cal sig?

Also, what can i do to prevent this in the future. Clearly its a training issue and i am sure i covered it in the beginning but i also understand things are forgotten due to inexperience. I had the 9mm handguns together on one table with the ammo; .40 on another table with ammo.

Thanks in advance

Ben

[Patton]

Most likely nothing bad. I have seen it in a few occasions. It will sound really weird. The craziest thing is the bullets would probably have hit their target.

[Jonnin]

Nothing too bad. You might split a cheap case, but the 40 is higher pressure and the gun can certainly handle the explosion of a 9mm. It should fail to cycle. Its hard on the gun to do it a lot, gas erosion of the barrel.

9 and 40 can share the same mags in some guns that have 2 barrels, if I am not mistaken ?

[Guest Cogent Design]

A buddy of mine told me a story about his friend loading a 9mm into his .40. The gun fired, but failed to cycle.

[atlas3025]

Yeah, not only is 9mm lower pressure, but it will generate even LESS pressure than in a 9mm Pistol because the bullet is too small to seal up in the barrel of a Fotay.

You can shoot a 50bmg out a 12 guage shotgun, and the same thing happens...though the stakes are a lot higher in that situation. NEITHER is recommended, lol.

[Jonnin]

Yeah, not only is 9mm lower pressure, but it will generate even LESS pressure than in a 9mm Pistol because the bullet is too small to seal up in the barrel of a Fotay.

You can shoot a 50bmg out a 12 guage shotgun, and the same thing happens...though the stakes are a lot higher in that situation. NEITHER is recommended, lol.

Nothing says get out of my house like.... a double barreled bmg?

[1gewehr]

You can shoot a 50bmg out a 12 guage shotgun, and the same thing happens...though the stakes are a lot higher in that situation.

DO NOT TRY THIS!!! A .50bmg round has as much explosive force as a hand grenade. The .50 cartridge is designed to produce pressures of 54,000psi. The 12ga shotgun is only designed for 15,000psi. Do you see the problem?

[Troutburger]

yeah and don't try to shoot a 30-30 in a .410 shotty either.

[atlas3025]

DO NOT TRY THIS!!! A .50bmg round has as much explosive force as a hand grenade. The .50 cartridge is designed to produce pressures of 54,000psi. The 12ga shotgun is only designed for 15,000psi. Do you see the problem?

Yes, yes, of course you shouldn't try it. I'm just pointing out the principle is the same. When the bullet is too narrow, the pressure is reduced. Of course

.

[Viracnis]

During my carry class the young lady behind the counter rented one of the other students a .40 for the class - but sold him 9mm ammo. He couldn't figure out why the rented handgun wasn't cycling and the recoil "felt weird". The gentleman running the class started to give him a hard time about squib loads and limp-wristing the gun. The instructor stood over him while he shot the next set, tapping and racking every time just like he'd been taught. After a 16-round magazine he reached into his range bag to pull out the ammo he'd bought from the instructor's wife and all became very clear.

Egg, meet face.

But as others have said, there was no real disaster. Just a handgun that wouldn't cycle, a really embarrassed small business owner and a whole class full of shooters that will likely never go back to that gun store / range.

Edited August 31, 2012 by Viracnis