The average black bear is not very hard to kill. The average whitetail caliber is all you need for your average black bear. Notice I"m saying "average."
I've killed 4 black bears. Of the 4, 1 was a big one at #10 for youth in Oregon, 18 15/16". I didn't get a live hanging weight as we skinned and quartered him in the canyon, but he was all of 400 lbs. I took this bear at about 200-250 yards with my 300 RUM, 1 shot and he slid on his nose. Glad I had that cartridge at that time for that big of bear.
My other 3 bears I have killed with a "lowly" 25-06 at 375, 440, and 450 yards. 2 of the bears took 2 shots to kill, the other took a single shot. I was using 115g NBT's on the 440 and 450 yard bears, and the 117g sierra gameking on the 375 yarder.
I believe in using enough gun to a certain extent. If you cant shoot a big rifle well enough to hit where you should be, then you should not be using it, as a smaller caliber with better shot placement will be more efficient.