For the love of god, it's a bear, you're a human

Unless you get a solid shot and have a high-powered rifle, you're just going to piss the bear off. Add to that, you're under duress because a huge grizzly is coming after you. A lot of cops have a tough time reloading their weapons under very high-stress situations, I can't imagine how a person, experienced with the weapon or not, would handle a situation like a grizzly stalking them.