.40 or .357Sig to 9mm Conversion - What Guns Work? - THR

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Old November 11, 2015, 02:02 AM   #1
Join Date: March 11, 2010
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.40 or .357Sig to 9mm Conversion - What Guns Work?

I've heard you can convert .357Sig or .40S&W Glocks to 9mm. Is this possible with other guns? M&P, CZ, Sig, XD, etc?
HGM22 is offline  
Old November 11, 2015, 08:37 AM   #2
Join Date: December 11, 2010
Location: Akron, Ohio
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357 Sig and .40 have the same case head dimensions. The problem with installing a 9mm barrel is that the breech face, ejector, and extractor are all designed for a larger diameter case. Not to mention they will have a stiffer recoil spring in most instances. For a range gun, it might be fine, but I probably wouldn't carry it.
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Old November 11, 2015, 12:25 PM   #3
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Agreed, for the reasons above. That's the advantage of something like a P250, where the entire slide is replaced. You get the added benefit of the sights being regulated too.

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Old November 11, 2015, 03:48 PM   #4
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Originally Posted by HGM22 View Post
I've heard you can convert .357Sig or .40S&W Glocks to 9mm. Is this possible with other guns? M&P, CZ, Sig, XD, etc?
Yes, It is possible with other guns.

For ex., Stormlake makes conversion barrels for 1911, Glock, M&P, XD/XDM

There are other conversion barrel mfg's too.

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Old November 11, 2015, 05:13 PM   #5
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M&P 40 full size and compact works fine with factory and (of course) purpose made 9mm barrels so long as you use 9mm magazines or bend the feed lips of the 40/357 magazines for 9mm (not recommended). The recoil spring is the same for 40/357 as it is for the 9mm, but the 9mm slide has more metal machined off and is a little lighter.

Consequently, spent cases from mid range 9mm loads (low to mid-1000 fps) in the converted 40 will not fly as far as with the 9mm slide, sometimes landing on your head or hitting you in the forehead. Full power 9mm loads (1100+ fps) work better.

About 6,000 rounds shot in the full size M&P 40 with the factory 9mm barrel. Sad to say that 100+ round accuracy is better with the 9mm barrel than with 40 mostly because of operator issues.
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Old November 12, 2015, 01:39 AM   #6
Join Date: March 11, 2010
Posts: 520
Thanks for the replies guys. Yes, the gun would be converted to 9mm for range use (cheaper ammo) and carried in the .40S&W set-up.
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