Taking Homers scenerio in mind which he's right the bear will be on you in a matter of seconds. I would choose one of two options.

Option 1 try to load your rifle again and get that one vital shot off being rushed and in panick. Not gonna be a great situation. But probally the quickest and most effective. Hopefully you'll stun him to the point of a follow up shot. Or kill it outright.

Option #2 One shot from a pistol before the bear grabs you and shakes you into lil pieces of flesh hanging out of it's mouth. I think if I get one shot from a pistol I'd probably want the biggest baddest thing on the market. I'd have to say 500 S&W. The chances of getting two aimed shots off using magnum class loads in a pistol in two seconds is doable but still got to consider the intensity of the situation.

I've been in one scrape with a bear but it was a black bear and I did have an advantage beings I already hit him once solid. But I got to tell you being 3 feet away from a bear still lively enough to get ahold of you is a feeling your not going to forget the rest of your life. I for one would pass on repeating that experience again. Just a note don't shoot bears on a steep incline straight above you they are coming down at you. Hehe the lessons we teach ourselves at some point in life. Me 1 the bear 0 I think i'm good with keeping those odds the way they are.

I've always thought of bear charge scenerio's. Do you draw your pistol and fire right away? Then have the bear knocked you down and there goes your pistol. Do you go to the ground and let the charging bear raise above you while you shoot? Will the bear roll you like a bull does? Will the bear automatically grab you and start shaking you losing your firearm in the process?

I would think most alaskan guides would know the answers. I say shoot while you got the chance. I'd rather get fined for killing a bear that was snapping it's teeth at me before the charge then wait to see if it's actually gonna charge you. Action vs reaction.