Many years ago, I read Elmer Keith's comments about pistols and bears. He said, essentially, that with any decent centerfire round, you would win a fight with a bear, if you kept your nerve.
Every bear opens its mouth when it attacks, shoot through the mouth and break the bear's neck. He never claimed you wouldn't get clawed or "chawed", only that if you kept your nerve, you would win.
I always thought that was probably true. If you don't have to shoot through the rest of the bear, any round suitable for personal defense against humans will break a bear's neck, but ONLY if you can hit it. That's where the keeping your nerve part comes in.
I used to shoot a lot of .44magnum level loads, and even more .45 Colt loads just a bit under .44mag levels. Depending on the gun, I could put 5 shots on 5 separate targets (bowling pins) in just over 5 seconds (semi auto) or 7seconds (SA revolver). Of course, the pins weren't running at me, either.
I know a number of people who simply cannot do this. I know a few who can do better. Too much gun is possible, and how much is too much depends on the skill of the shooter. Also helps a lot to know bear anatomy. Unlike the sleek tailored looking cats, Mr bear wears a shaggy, sloppy fitting suit. His vital spots aren't quite where most people think they are from looking at him.