[Futo Inu]

I think so, but want to make sure? If so, then no need for extra bbl in .40, correct?

[Black Snowman]

I would imagine you'd have feed problems and there would be problems with headspacing. The only thing holding the round in place would be the extractor which could lead to ignition issues. Plus you have the nice sharp ridge the bullet has to fly past before actually reaching the barrel. Also it probably wouldn't produce enough slide velocity to cycle properly. It would be a lot safer and more reliable to reload light 10mm loads than it would be to shoot .40 S&W through a 10mm gun. For the reasons listed above I recommend not even attempting it.

The only gun I know of that can shoot both is the S&W 610 revolver as it uses moon-clips to hold the rounds in place and doesn't use the mouth for headspacing.

[Sean Smith]

Perfectly safe to shoot .40s&w from a 10mm auto, semi-auto pistol?

No. Get a .40 S&W barrel or just load 10mm light.

[Futo Inu]

Yeah, I've always wondered why people would recommend doing this without the slightest apprehension of the sharp edge of the front of the chamber coming into contact with the bullet, but I figured they must've known something I didn't - but certainly it DOES seem to me that this could cause some sort of instability, or deformation of the bullet (which could affect external ballistics), or worse, that the bullet could be thrown sideways enough to actually create a dangerous high pressure sitation - after all, it's not like the easy taper of a revolver's forcing cone, in the transition from the chamber to the bbl. As far as light primer strikes, yeah, I'll bet you're right on that too since the ejector is only on one side and the cartridge can therefore tilt forward from the far side opposite the extractor, preventing a solid strike. Also, I wonder if it might not be possible to have the cartridge on rare occasions somehow completely miss the extractor, then the cartridge is entirely within the chamber, also guaranteeing no ignition. Bad idea - I could have just sworn I'd seen people recommending this a few years back - lol - I probably just don't correctly remember the exact topic - ha. Okie - doke.

[TIR]

I have done this in my G29 which wouldn't feed them do to the extractor being the only thing holding the casing. I manually racked the slide to get them to feed for 5 or 6 rds. to see if it was accurate at all. It wasn't and the casing had alot more unburnt powder in them than through one of my 40 s&w guns. I would not recommend it nor will I be doing it again.

[Lancel]

Once upon another decade, when I had enough knowledge to feel smart but not enough to be wise, I did the following:

Test fired a full hicap magazine of .40 S&W through a 10mm Glock 20 without any failure to feed or fire. Also test fired a handful of .40 S&W through 10mm Contender without problems. Lucky me, this was unsafe.

It is NOT like .22 Short/.22LR, .38 Spl/.357 or .44 Spl/.44 mag. Those cartridges headspace on the rim. The .40 S&W is rimless and headspaces on the case mouth not the rim.

Since the .40 in a 10mm chamber is being held by the extractor hook and not getting proper headspacing bad things can happen. As I understand it, a long firing pin could perforate the primer breaking that seal that keeps those hot gunpowder gases under control. Or the firing pin could push the shorter cartridge forward before detonation causing the primer to have enough space to get pushed out of its pocket, again breaking the seal.

The end result could be parts in your face and feces in your pants.

Larry

[CaesarI]

TGZ has a very good (old) article on the matter:
http://www.thegunzone.com/10v40.html

Short answer: Bad, bad, idea.

-Morgan

[C.R.Sam]

Might get away with it.
Might not.
Your face, hands, eyes etc.

Don't.

Sam

[caz223]

Aftermarket .40 barrels from reputable manufacturers are cheap these days, a lot cheaper than one visit to the med-center.
I can't see an upside to shooting .40 in a 10mm, unless it's a smith 610.

[loudernhel]

I've tried it for a few rounds in my new G20 and it works fine, although the empties hit me spang between the eyes.

However, the replacement barrel is cheap so for frequent practice use of the lower power ammo, just buy the barrel and you know you'll be safe. That's what I'm going to know.

However, it is good to know that if I have to fight off hordes of evil mutant zombies or something and run out of my 10mm loads, I can scrounge the much more common .40 round for use in exigent circumstances where the risk of using the .40 in the 10mm chamber is outweighed by the risk of not being able to fight back.

[caz223]

In a dire emergency, you could always shoot 357SIG too, but if you prepared a little, you could have the appropriate barrel stowed somewhere close enough to get at it.

[denfoote]

I went through the same gyrations and got the conversion barrel!!!
It was only $135 plus $25 to have it custom fitted to my G29.
If you are going to do it, do it right!! :D