Despite being made virtually identical, its not unheard of that individual pistols of the same make and model will favor different types of ammo, and so will shooters. As the original .40 round was a 180 grain bullet moving at around 900 feet per second, use that as a baseline. Lighter weight hollow points will likely move faster, but may also produce larger shot groups. That is pretty much standard with all calibers. I have little to no experience with the M&P 40s, but have not noticed much difference in the accuracy of 165 and 180 grain bullets, either hollow point or ball out of other 40 pistols. From the specs I've read, the lighter 135s and such have a higher velocity and higher muzzle energy, but the groups spread out. It terms of function, most all factory loads will work in any modern pistol, but you'd better try them first to make sure. My full size 45 does not seem to like 185 grain ball as well as it likes 230 grain stuff. The differences are subtle, but I'd use 230 in competetion or for defense when I really didn't want to take the chance of having to clear a malfunction. Enjoy your pistol.