I have an M&P40. I just ordered a factory 9mm (it's actually back ordered) for about $66.
Can't wait to try it out in a month. I originally bought the .40s&w because I heard you can go from .40 to 9mm, but NOT from smaller 9mm to larger .40. I doubt I'd purchase the .357sig in the future. No need to. The pistol is more accurate than I, so I couldn't see spending double for the StormLake barrel.