My only experience with bears in nearly 40 years of hiking, hunting, fishing etc. is normally the south end of a black bear heading north of me very quickly so I for the most part don't give them much thought but watching the shows on tv about the really big and bad ones I have to question ones ability to be able to hold a handgun steady, take careful aim and shoot accurately under what might be a very sudden and frightening encounter. Regardless of the caliber unless one had a considerable amount of regular practice I'll bet the chance of a kill shot is in the single digit percentile.