I get the notion that a .45 is adequate IF the shots can be well placed. Disabling a bear’s hindquarters would probably necessitate a good spine shot, but in a close situation, that would be hard to accurately place. A big Magnum gun should give better odds.
I have shot bears with rifles. shotguns and handguns.
Good shot placement is the key to make any of them work.
Proper bullet ammunition selection helps also.
I am always torn between raw power and controllability.
Follow up shots with full power magnums loads are a lot slower to do.