Just my opinion but a .357 should be fine for a black bear
I agree. Black bears are not that big and tough and generally are much quicker to run away than be aggressive. I spend a fair amount of time in a fairly remote part of Colorado that has a lot of problem bears. It is one of the places problem bears are relocated. I have only come close to having to shoot one once. They are generally not that hard to scare off. The ones that were the biggest problems, over the years, were a couple that a local lady felt sorry for and fed. All she really did was sign their death warrant.