aggressive black bears
A black bear is a wild, formidable creature, up to 600 (that would be a VERY big blackie) or so pounds of teeth, claw and muscle, and should not necessarily be trusted. But I'd have to disagree with the "aggressive" comment. True, there are black bear fatalities and injuries. But they are far from the norm. The Smokey's receives something like 13 million visitors annually, its the nations most visited National Park. Over the years quoted in an earlier post, the visitation would be in the hundreds of millions. From that there were what, 107 injuries.?
I no longer live or work in black bear country, but did for a while and had some interesting opportunities participating in black bear studies and relocating "problem" bears in Shenandoah and Great Smokey's. As with any animal, they can definitely get brazen if they become accustomed to humans. And humans ( myself included) can do some brazen and stupid things if they get accustomed to bears. That's for another post. Much of that has been resolved once the parks got a grip on handling trash, and relocated the real problem panhandlers. The "yogi" bear jams are largely a thing of the past.
To the OP. A .357 revolver loaded with 158 gr or up would be plenty for deer. Much depends on the placement of the shot of course. Average black bears are likely closer to 300 lbs +/_ and the .357, loaded heavy, though not optimal, should work there also. I would stay with SWC penetrators for bears, due to the larger bones, hair, hide, fat, muscle make up on bears, as opposed to a JHP. JSP's might be a happy medium.