I don't know if I'd have the balls to try it but apparently the head of many animals is a weak spot, who would have thought?
They say that if you draw a line between an animals left eye and right ear, and another between the right eye and left ear, where the two intersect is the best place to kill that animal with a single blow.
Don't know how true it is, but looking at bear skulls it's got some validity i guess
Black bears aren't all that tough, compared to grizzes. And they don't have that same 'fight to the death' mentality.
There is actually a recorded incident of a 7 year old girl driving off a large black bear with a wood axe.
And yes - there have been several stories (one just a couple of years ago) where a man was able to kill a bear with a knife in an attack. I asked about what kind of knife the guy had in that incident and found out it was some cheap thing, not even a particularly good knife

too bad - some knife manufacturer would have made out really good there

"our knife can kill a bear, and still slice tomatoes THIS thin....."
But if we're talking about actually choosing a gun for bear defense, then the biggest, widest, most bone-breaking hole you can put in them is obviously best. If we all had unlimited money, unlimited time to practice, and didn't feel recoil, that's what everyone would want.
sometimes you gotta go with what you've got - but most people could at least afford a good ole maverick shotgun and slugs.
Pick the biggest gun that you're comfortable practicing with regular given your budget (even if that means one in your closet right now because you can't spring for a new gun), choose the best load for it, and pratice.
But like someone always says at the end of these - your brain is still your very best defense against mr bear. Use it wisely and you probably won't have a problem.