switching a m&p from 357sig to 40? ????

[hoverking]

What all has to be done to do this with no issues, can find posts going from 40-357 but none the other way
Im guessing just getting a 40 barrel would do the trick

 

[Elkins45]

Are the mags specific to 357 or are they generic 40/357? I know that Sig marks their mags for both, but Glock 357 mags have different lips than the 40 version. 40 mags generally work fine with 357 rounds, but the non-tapered 40 might not fit in a 357-specific mag.

My guess is that if you can successfully fit the rounds in your existing mags then all you need is a new barrel.

 

[Tex1001]

All you need for the full size M&Ps is a barrel. 40S&W barrel drops right in on the 357Sig slide. Midway sells them cheap. Mags are interchangeable between 40 and 357. They're marked.
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[vegasgunhand]

Like Tex stated, all you need is the new barrel. I bought a .357 Sig barrel for mine, when a friend gifted me several thousand rounds of Speer Gold Dot JHP. Works like a champ!