I know several people who have used buckshot on Black Bear, with excellent results.
I have always been fond of #1 and #4 buckshot....
Buckshot is a "woods" gun. Closer range, but it is excellent on deer, hogs and just about anything else that you see in the woods. It is not the right tool for coyote, as you would rarely if ever be close enough to use it. Any kind of small game would also have to be close and IF they were close would be blown to tarnation....
This is a guess, BUT most of the time I hear about buck shot doing poorly, I think that they may have not taken the range limitations seriously enough. If buckshot is used at anything approaching 50 yards, it's effectiveness drops considerably.