My thought is.....
I'd hate to spend the time and money to go on a bear hunt and have my only shot at a mature bear be at 75+yds...knowing full well that the shot is not one that should be taken. (Some would, but it's a mistake)
Buckshot will kill bears...UNDER 50 yards. It will kill them further, but not consistently enough for me.
If it were me, I'd opt for buying or borrowing a rifle. Probably half of all hunters have an old 30-30 sitting in a closet somewhere. They are an incredible bear rifle under 150yds.
Good luck.