In the time allowed, shot placement rules. This is similar to discussions on some gun forums about stopping an attack vs killing an attacker. A .22LR can kill an attacker, but maybe not fast enough.

A bear's physiology allows it to keep moving quite a bit longer than it takes to attack and kill a mere human. Then the bear moves off and the blood pressure drops off and it dies. We're back to putting rounds in the brain for an effective stop and that is much easier said than done against a fast moving bear.

I'd go with bear spray too.

YMMV <$.02