Help a newbie out please. Looking to buy some ammo for my new handguns (S&W MP9mm and Sig P226 9mm). Was going to buy blazer 9mm ammo, and just noticed they have 115gr and 124gr ammo. Can somebody kindly explain the difference between these two and which is appropriate for using at the gun range? Also, my first time going to range, is FMJ ammo accepted at all ranges? Thanks!