I have used Winchester 572 powder in 38 special, 40 S&W, 45acp. I worked up loads from Hodgdon's data center site. 572 is not listed if 357 magnum is chosen.
If you go on Dillon Precision: Reloaders, Reloading Equipment, Bullet Reloading, Bullet Reloaders on their forum section you will see 650. I thought i saw a while back this question asked and Dillon replied to clean powder bar with alcohol and funnel too.
In the box the gun came in you should find the manual and a yellow envelope with spent brass. it should have a date when it was test fired.
Good Luck on your new M&P. My son and I both have 40 FS and love them. No problems.
Brain, the prive sounds good. I have the FS 40 and it has not given me any problems. as you shoot try each backstrap to see a difference which one you shoot best with. Smith-Wesson has life time warrenty so don't worry. Enjoy it. Tony