I know a guy in alaska who guides, famous guy, his daughter is plain out spooky at guiding too. She maybe better than him. She carries and has used a .357 mag loaded with 180 grainer hard casts. In shooting a nuisance bear that had broken in to a few camps, they later propped up the bear and shot him several times to determine effectiveness on the dead bear and found that 180 grain hard cast penetrated just as deeply as 270 hard cast 44 magnums and 300 grainers from a 45 Cassull. Sometime later she was guiding some fisherman when a large adolescent male refused to leave them alone. Spray, whistles, firecrackers did not scare this bear away. When it closed to within a few yards and made a couple of false charges, the woman finally shot. Three .357s in the head, one of which entered the eye, dropped the bear at her feet. She was fine, at least one of the customers needed clean clothes.
As far as black bears, two summers ago in Quetico canoe area, we had a black bear that had NO fear of humans in our camp. Spotlights, bear spray, two cherry bombs, and lots of guys screaming like idiots at the bear did not phase it all. We left after we found out that it was stalking one of the party when he walked down to clean fish. This was a full grown bear. Maybe 300 pounds. He could walk if he wanted to silently. One of our party had the bear spray that also had the dye in it, we tied that to a tree and got a really good shot on the bear as he walked past using a string to pull the trigger. We left that campsite before dark as we decided that if he was that fearless in the day time, what would he be at night and us asleep in a tent. We reported the behavior of the bear to the park service when we pulled out.
two summers before that in the BWCA we had a black bear push over a 10 inch diameter poplar that we had tied our food packs in. Another guy showed us pics of the trunk of his car after a black bear had decided that it contained something he wanted. The bear stood on the car and got its claws in the trunk lid seam and literally pulled the trunk lid off the car.
If i have to deal with a bear I want as a minimum a 44 mag carbine. I will carry a 44 mag pistol but I want bigger readily available. I would love to see what a 500 S&W or a 460 S&W would do out of a trapper length carbine.