That's a good question, depends on the size of the person using the gun
I'd recommend a large caliber revolver, 44 magnum and up, so that it never jams in a time of need, with hollowpoint rounds to maximize size of wound. If your are worried about bear attack make sure the revolver fits your hand so you can have a good, controlling grip on the revolver and that you can practice and can shoot accurately with it without flinching from the recoil.
many will 'kill' it but if you were hunting them or in a situation of self defence you want something with enough knock down power. a .300 win mag with the right bullet would be sufficient but many would argue a bit more, .338 win mag or ultra mag may be a better choice.
.44 magnum. Right between the eyes. Its lights out. Within a decent range of course. If you miss you die.
Not really. Typically, grizzly bears are big and very heavy. A larger more powerful caliber would be a better choice.
.357
A gun of a human
Black Bear.
black bear
the californian black bear.
Use the final fall gun.
fish
To the best of my knowledge unless you are a convicted felon you can own a black powder gun.
ak74u
very well placed shots from a very skilled shooter could potentially bring down a black bear, however a 9mm is not the gun of choice.
Porters x2 ray gun and zuse cannon
use the ray gun or the thunder gun
M14