The biggest problem is that hunters usually let the bears psych them out and they don't shoot straight. I've been hunting bears of all varieties for over 20 years in AK and Canada, and a .270 is plenty fine to kill them if you calm down and shoot them in the heart. A .270 is not a bear stopper, but it is a bear killer. If you honestly expect to stop a charge (which rarely, rarely happens despite the hooror stories that 'always happened to a freind of a friend'

, you need something in the range of a .404 Jeffrey or bigger.
Make the first shot a killing round. The BS about 'breaking them down' first has resulted in more wounded and lost bears than I care to think about.