Shooting .40 S&W in a Glock 10mm Auto

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john_pifer

john_pifer

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I've been hearing for years that this is possible for years but have been hesitant to try it, until I came across this article:

http://www.thetruthaboutguns.com/2015/06/jeremy-s/40-in-a-10mm-glock/

I could find no holes in his argument, so I went out and bought a box of .40 S&W and ran it through my Glock 20 (chambered in 10mm Auto). As expected, zero problems, and the .40 S&W ammunition is a joy to shoot out of the big G20 (10mm is also pretty tame out of the G20 if you're used to shooting quite a bit).

I plan to continue shooting .40 out of my Glock 20. It's nice being able to go to Wal-Mart and buy .40 for $14/50 rds as opposed to having to order 10mm Auto ammo online, or go to a gun shop and pay well over $20/50 rds.

Here are some comparison groups I shot from 30 feet with some PPU 10mm Auto ammunition vs. some Perfecta .40 S&W:

 
Originally Posted By: Kuato
Interesting. How close are the measurements between the two rounds?


.40 S&W case is ~ 3.5mm shorter than a 10mm Auto case.

Read the whole article when you have time - he goes into detail, explaining every facet of this.
 
Originally Posted By: tomcat27
your target is hilarious


Yep, now I can say that I can, indeed, hit the broad side of a barn!
 
Originally Posted By: nwjones18
That is interesting. I have several S&W 10mm's but no glocks yet.. When I want to shoot a .40 though I just take a .40 to the range.. haha


Yeah, I would, too, if I owned a gun chambered in .40!

I really like the look of those older S&W all-metal DA autos. Would love to shoot one sometime.

Since you own several, you'd probably enjoy this article on the 1006 that someone posted up, over on the 10mm forum:

http://10mm-firearms.com/10mm-semi-auto-handguns/complete-article-on-the-development-of-the-sw-1006-(july-'89-shooting-times)/
 
There are at least a couple of reasons why it’s not a good idea to shoot 40 S&W in guns chambered for 10mm. But since it can be done, some people will insist on doing it. Anyone wanting to understand the pitfalls, can find it easily with a search.
 
Originally Posted By: Brian Barnhart
There are at least a couple of reasons why it’s not a good idea to shoot 40 S&W in guns chambered for 10mm. But since it can be done, some people will insist on doing it. Anyone wanting to understand the pitfalls, can find it easily with a search.


Yeah? Like what?

I've researched it enough that I'm willing to bet whatever "pitfalls" you mention, he's probably addressed thoroughly in the article.
 
Originally Posted By: john_pifer
Originally Posted By: Brian Barnhart
There are at least a couple of reasons why it’s not a good idea to shoot 40 S&W in guns chambered for 10mm. But since it can be done, some people will insist on doing it. Anyone wanting to understand the pitfalls, can find it easily with a search.


Yeah? Like what?

I've researched it enough that I'm willing to bet whatever "pitfalls" you mention, he's probably addressed thoroughly in the article.

Ignore what Glock recommends. Ignore what the ammunition manufacturers say. Neither will recommend the practice. Do whatever you want.
 
Originally Posted By: Win
Interesting, indeed. The .40 had no trouble cycling the G20? Did you use the G20 mags?


Yes, G20 mags. No malfunctions of any kind.
 
I was kind of thinking along the same lines as OneEyeJack. When I shoot .38s in my .357 revolvers, there's a buildup of carbon crud near the front of the chambers due to the shorter case. If I then try to shoot .357s afterward without scrubbing the chambers real good, I can have some problems.

I would think you might run into some feeding issues if you shoot a bunch of .40s and then switch back to 10mm ammo without a good barrel cleaning. I haven't read the article yet though--maybe that's addressed in it.

Regardless, probably isn't a big deal unless you shoot real hot 10mm ammo after a long string of .40s without cleaning.
 
Originally Posted By: OneEyeJack
Is this the same kind of idea as shooting 38's in a 357?

Same idea. But not the same in practice due to the difference in headspacing methods.
 
Originally Posted By: OneEyeJack
Is this the same kind of idea as shooting 38's in a 357?


Similar but not the same. Please read the article in its entirety. Everything is explained.

Note that he does not recommend this in any 10mm pistol besides the Glock, due to the unique way in which a Glock functions.
 
Originally Posted By: Brian Barnhart
Originally Posted By: john_pifer
Originally Posted By: Brian Barnhart
There are at least a couple of reasons why it’s not a good idea to shoot 40 S&W in guns chambered for 10mm. But since it can be done, some people will insist on doing it. Anyone wanting to understand the pitfalls, can find it easily with a search.


Yeah? Like what?

I've researched it enough that I'm willing to bet whatever "pitfalls" you mention, he's probably addressed thoroughly in the article.

Ignore what Glock recommends. Ignore what the ammunition manufacturers say. Neither will recommend the practice. Do whatever you want.


I see you provided zero reasons as to why this isn't a great idea.

Give some reasons and I'm perfectly willing to have my mind changed, Brian.
 
Originally Posted By: AlaskaMike
I was kind of thinking along the same lines as OneEyeJack. When I shoot .38s in my .357 revolvers, there's a buildup of carbon crud near the front of the chambers due to the shorter case. If I then try to shoot .357s afterward without scrubbing the chambers real good, I can have some problems.

I would think you might run into some feeding issues if you shoot a bunch of .40s and then switch back to 10mm ammo without a good barrel cleaning. I haven't read the article yet though--maybe that's addressed in it.

Regardless, probably isn't a big deal unless you shoot real hot 10mm ammo after a long string of .40s without cleaning.


Indeed, he does address that point in the article.

Yes, you're quite right - it's advisable to keep the chamber and barrel clean when doing this.
 
Originally Posted By: OneEyeJack
Is this the same kind of idea as shooting 38's in a 357?


Sort of, except that revolvers index off the cartridge rim, and in this case, the auto is indexing off the extractor. But the .40 was created by shortening the 10mm, so it's similar to the .38 SPL/.357 Magnum relationship.

I've read the same article...and decided not to shoot .40 from my G20...but then I've got a few .40s including a G23. I've got two barrels for the G20, a compensated and an uncompensated...perhaps I should consider dedicating one to shooting .40...

The PPU 10mm is what I shoot the most out of my G20. It's mild, at 180gr and just under 1100 FPS. I've put a few hundred rounds of Buffalo Bore through the gun, and at over 1300 FPS for the 180gr, there is considerably more recoil (and terminal performance).

I've paid about .42/round for the PPU. Best deal I've found for 10mm.

My last batch of .40 I bought for .24/round, so there is considerable difference in cost.
 
Last edited:
On my phone and so too hard to read the article, but .40 S&W cartridges need full chamber support. As long as the Glock does that, then fine, but I know that not all manufacturer's do for .40.
 
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