M&P Magazine Interchangeability

[BigBoy99]

My brother-in-law just bought a S&W M&P in the .357 SIG caliber. He wanted to get some spare magazines for it but he couldn't find any. My question is, could the .40 S&W magazines be used for the .357 SIG ammunition? Since the base diameter of the two rounds is identical, one would think the magazines would be identical too. Since the feed ramp is on the frame, one would think that correct feeding could be done by either magazine.

Also I have heard S&W has dropped the .357 SIG handguns from their latest catalog. How hard would it be to convert to the .40 S&W caliber? Would a barrel change do the job?

Would appreciate any help as I'm am unfamiliar with the new S&W handguns as I prefer the older ones. Thanks.

 

[MSG Glenn]

They're identical, Bill. Take a look at the front of the mag. It says "40S&W, .357".

 

[lhump1961]

As MSG Glenn said they are the same mag and completely interchangeable. Before I got my .357c I was thinking of simply getting a .357sig barrel for my 40c but was concerned about the increased pressures with the .357sig. I called S&W and was told that the only difference between a .40 and a .357sig in the M&P line was the barrel and to have no worries about interchanging the parts.

 

[uechikid]

FYI. Midway USA has M&P 40 barrels in stock.
Smith & Wesson Barrel S&W M&P 40 S&W

 

[lrmnut]

What about the M&P 9 mag and frame are they interchangeable also?

 

[BigBoy99]

Appreciate the Help

Thanks for the info. I'll pass it along to my brother-in-law. He can widen his search as he was looking for just the .357 SIG magazine. I guess no one told him the .357 SIG and .40 S&W calibers were interchangeable.

I'm going to try to convince him to get a spare barrel in .40 S&W caliber so he can have a more diverse weapon.

 

[Lost Lake]

What about the M&P 9 mag and frame are they interchangeable also?

The 9mm mag fits the .40/.357 frame.

With a 9mm barrel in a 40/357 you can reliably shoot 9mm all day long.

.