M&P 9mm to 40 conversion? Seems to be possible

[BobBarker]

Didn't think you could do it, because the .40 barrel you would think would have a larger outside diameter than the opening in the 9mm slide, but apparently that's not true. Seems to be you can shave down an internal part on the slide and the cartridges should be able to feed. Also, seems to be popular thinking that you need an expensive conversion barrel to change from .40 to 9mm but that doesn't appear to be true as Storm Lake's rep has stated that the conversion and replacement barrels are the same. Check out this link:

http://mp-pistol.com/boards/index.php?showtopic=26633

 

[inactive]

The replies are way off-base of the OP's question in that thread. He started talking about starting from a 9mm and going to 357 Sig, but the replies are all discussing going to a 9mm, which is easily and commonly done on .40 and .357 pistols of various makes. Going up compared to going down in caliber are two very different things.

Outside of the barrel, the breechface sizes in the slide are different. I wouldn't try it (converting up), even if it seemed to feed and extract, and I doubt it would. (can't say as I have not examined an M&P closely enough).