People up here kill bears with .223's when they have the upper hand and opportunity. When the bear is attacking you, the .223 is not the weapon of choice, neither would be a .300 BK or 6.8 SPC. Better than a sharp stick, but not the best choice.

A .458 Socom is the ballistic equivalent to a 45-70 medium/light load. A 45-70 is a highly regarded lever action round for up close bears with full power rounds. I wouldn't feel too undergunned with a .458 socom.