Old Moss,
I would not get a single shot at all. Too slow !
For a long gun, a double barrel shotgun, or double rifle might be as good as anything since it seems that in a real charge it is unlikely that you would have time to get more than 2 shots off anyway. EAA makes a double barrel twelve gauge that you can also put 2 45/70 inserts in and make it a 45/70 double rifle. Or you can use one shotgun barrel and one rifle insert for a 12ga/rifle combo. The big plus for this combo is that it is a great survival tool and can also serve in a defense sitation if needed.
You get the most knock down power with a bolt action, but it might as well be a single shot because the recoil and action type make it slow to cycle especially under pressure with the long magnum rounds. If I were going to carry magnum round, I would carry a double rifle but the ones in those calibers are really EXPENSIVE.
But if I were in big bear country on a regular basis, it would be a 45/70 lever action or a pump shotgun. Speed for repeat shots, adequate knock down power, and plenty of shots on tap so that if you slow the big guy down with the first 2 shots, you have 3 or 4 more to finish the job.
As for a handgun, I would carry the biggest double action revolver I could shoot one handed with my weak hand (the strong arm may be in the bears mouth by the time I am reaching for the handgun.) For me, that is a 4" Dan Wesson 445 Supermag (I can always shoot 44 mags in the same gun if need be or 44 specials for small game for the camp pot.) I am also building a ported 445 Supermag lever action which I will use for bear protection up to 600lb to 700lb bears. For the really big ones, it will be the 12ga with Brenneke premium slugs (and maybe a steel BB load up front) or a 45/70 PORTED guide gun stoked with Garretts 540gr Hammerheads.
Those are my present thoughts on the subject anyway.
To All:
Thanks to all who have offered responses. They have been very helpful to me.
Roll Tide