For a handgun, at least...in my case, a handcannon. This is my 4" (Really 3" with a 1" comp) .500 mag. I handload a 400gr reduced recoil load that is downright pleasant with 11gr Trail Boss (recoils like a .44 mag on steroids, but 100% controllable), and a 350gr jacketed SP with 42gr of H110/296 that will physically split the skin from the web of your hand through a thick Mechanix glove after a few cylinders. I can't think of something else that is this violent (and way too much fun) to shoot. What is you folks worst kicker?