Smith and Wesson M&P 9mm - 40S&W

[iMoses14]

I own a Smith and Wesson M&P 9mm fullsize (4.25" barrel) for home defense.

Can I put a 40S&W barrel in my firearm? Or, can I only go from a 40S&W down to a 9mm?

Make sense to anyone? It kinda confuses me but I'm running on no sleep cause of the new baby. Lol.

[hankforker]

You can not place a 40 barrel in the 9 slide. It may be possible to change out the complete slide assemblies as I believe the frames are the same dimensions but I am not certain. Someone will chime in with more expertise I am sure.

[QuackXP]

I just purchased a S&W 40 and I have done a significant amount of research into this firearm.

Sorry to bust your bubble but you can't convert 9mm to .40. By a barrel swap only.

There are conversion barrels avaliable from Storm Lake to convert .40 to 9mm. You also need 9mm magazines to accomplish this.

Check out http://mp-pistol.com for a detailed explanation of why this is and what measurements cause it to be that way.

Also the M&P .40 can take the factory .357 Sig Barrel and the .40 and .357 sig magazines are the same. The magazines bare the markings for both .40 and .357 sig.

Aside from a larger caliber the easy conversion to 9mm was one of the main reasons I got the .40 over the 9mm.

I don't think changing out the entire upper is cost effective, but I do believe it is technically possible. I was looking specifically at a barrel & mag swap solution.