Are black bears hard to kill..... Nope.
Like jerrygoat states, there vitals are smaller than anticipated, that has lead to not the best of vital hits in my experience.
Another thing with bears is the layer of blubber they have in the fall sometimes will close off exit wounds to an extent also. That can make trailing a dead bear a chore at times
I have not killed no where near the bears Ralph Young has or have seen killed. I do know they die very well with a good ol'brain pan hit 'my favorite' or the ol' fashioned heart/lung shot with just about any caliber that you shoot deer with
