All of those M&P barrels I have measured have been right where they should be, so a .356" bullet will work. But measure yours first and make sure. Recently I have been shooting the Lee 358-125-RF in the 9mm, sized accordingly of course, with great results. It has a nice nose shape to feed in autoloaders. Lee also makes several good designs in 6 cav. style worth looking at, and the tumble lube ones are especially useful if you shoot large numbers of bullets. Tumble lube with 45-45-10 and they won't be tacky or build up lube in the seating die or gun. Lots of good choices out there for that pistol.
