Although most of the time a black bear will go the other way, certain circumstances will make them charge, first and formost, cubs, if she thinks her cubs are in danger, she will tear anything in her path up, I once saw a vidio of a small female " 300lbs range", take on a boar almost twice her size and kicked his but!, second, if they feel cornered. My personal oppinion is a .44mag or bigger, I would think a 40 or even a 45acp with a heavy hard cast bulletwould do the trick or at least slow it down, but I would rather have the hand canon and a roll of T.P.