We spent a couple of months time in Montana and Wyoming during the 90's 4x4 base camping by rivers and streams, a fave the Bob Marshall Wilderness where one fall trip we saw a big grizz most days fattening up on berries a couple hundred yards downriver. A Mossberg Marine 12 ga was always in quick reach.
Per the advice of a black bear hunter we had met when getting our Montana fishing licenses, the first five shells going into chamber were sabot rounds for distance followed by 000 for in your face range.
His advice that because grizzlies were so freaking fast on the charge, the moment one turned toward your let one round off hitting something close to the bear, which gave you target distance and warned the bear, and than be prepared to fire on the bear the moment it began any continued movement towards you, justifying the shooting afterwards if still alive.
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