.40s&w in a 10mm

Most rimless pistol cartridges headspace on the end of the cartridge. The only way the .40 could fire in a 10mm is if the extractor would hold it close enough to the breech for the firing pin to strike the primer. If it worked, then the newly fired case would pound it's head against the breech with every firing since the extractor is not meant to hold the head tightly against the breech.

10mm's have stronger springs in the slide, so the next issue you will face is if the 40 would cycle the action.

I recommend not trying it.

It can be done, I've tried it just because. But it may or may not cycle the action, typically won't feed properly, and if the extractor doesn't grab them, it'll go too deep in the chamber and most likely not fire at all.

So yes, in a pinch it can be done. But it's not an adviseable practice.

Don't put the wrong ammunition in any firearm. Just don't.

Para Ordnance made a dual caliber 10mm/.40S&W 1911 years ago, it had twin extractors to keep a firm hold on the cartridge during, feeding, firing and extraction.

The Smith 610/310 10mm revolvers can also fire .40S&W with moon clips.

Shooting .40S&W out of 10mm Barrel

OK, to be fair and honest, there WERE 2 failures to feed in the second gun, the G21. I have spent so much time arguing with folks about the feasibility of this that I was intent on the shooting only, not the feeding. Having a couple of FtF's in a .45 with 10mm bbl shooting .40 ammo doesn't really disappoint me. The successful firing of the.40 in the 10mm bbl was what this was all about to start with. I did add the forward grooves to the slide so it wasn't really "stock" but my point was that there was nothing done mechanically to the slide to affect the test.

I'll take your word on the 9x18. I wouldn't have thought it would chamber all the way.

The Smith 610/310 10mm revolvers can also fire .40S&W with moon clips.

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I can attest that both calibers chamber and shoot well in the S&W 610. Moon clips required for the .40; advisable with the 10mm to make extraction easier.

Well since the cartridges are so nearly the same could this not be done with a quick switch to a .40 barrel and lighter recoil spring?

Well since the cartridges are so nearly the same could this not be done with a quick switch to a .40 barrel and lighter recoil spring?

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Yes, it can and you do not need to change the spring

You could probably do it, but it's not completely safe and I don't recommend it.

Didn't we just have another thread about this?

Why would you think it is not safe and why would you not recommend it? There are a number of companies that make the 10mm/.40 conversion barrels just for that purpose. Maybe you should notify them with your concerns. Their engineers probably aren't knowledgable enough to know any better

machIVshooter said:

and if the extractor doesn't grab them, it'll go too deep in the chamber and most likely not fire at all.

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if you're lucky. i mean think if the firing pin hits and the case goes slamming back to the breach and probably piercing a primer and damaging a firing pin. but maybe the cartridge just says there and your attempt to clear it pushes another round behind it.

doesn't sound fun.

I shot five .40 rounds in my first Glock 20 just to test it. It worked fine. Then I bought a conversion barrel and used that quite a bit before I started handloading.