I'd take a 3.5" 12 ga vs. a .300 at 25 yards on a bear any day of the week.

All you have to do is shoot a block of ballistic gelatin at close range with both weapons and look at the wound profile.

Not to mention having to deal with a scope or even iron sights while a grizz is bearing down on you at about 25 mph. You can't beat the pointability of a shottie in close quarters.