I wonder how many of the posters on here have actually shot a black bear.....
I have. Decent sized brown phase blackie.
Two shots with a 7mm-08 w Hornady Ballistic tip (can't remember the bullet weight it was almost 10 years ago) although the first would have stopped him as a threat.
First shot was bad, I was only 14rs old and had just ran my balls off up a steep hill and the bear was running about 75 or so yards away, so that shot hit him in the spine and severed it, put a hole about the size of a child's first through him. I don't believe in allowing harvested animals to suffer so I made a second shot. The bear was thrashing around facing me, I was aiming for his throat but hit a bit high, right into his upper jaw through that and into his brain shattering his skull (I can post a pic of the skull if anyone wants to see it, the taxidemist had his work cut out for him gluing it back together lol) dropping him instantly.
Any decent sized deer rifle will work against bear with proper shot placement, although for defense if I were stuck out in bear country I'd want a semi-automatice in a larger caliber such as a .308 FAL/AR10/M1A or .30-06M1 Garand.
I have a friend who is a firearms instructor who did bear security for a survey crew in Alaska and they limited him to his Remington 870 with slugs... he said he REALLY didn't like that arrangement and would rather have had his FAL.