So - I have learned over the years that if you take ten people out in the field to do field research, maybe half of them have ever shot a gun before. An afternoon spent blasting clays with a shotgun, and an hour learning to aim slugs out of a shorter gun is all you need to get the confidence for someone to carry a gun, and potentially use it, safely. When out and about, you typically are not alone, so two people with shotguns as opposed to one. Reloading in a bear encounter seems very unlikely, as well, but I still carry spare ammo. Teaching someone to shoot an AR10 or a handgun is more involved.
That's for the temporary use. If you live someplace with bears, it might make more sense to have a semi-auto rifle in .308, but you're still lugging a heavy gun and relying on multiple hits to bring down your target. I mean poachers take elephant with AK47s and FALs all the time in Africa, but often on full auto. PHs and local governments don't let folks hunt elephants with anything less than a .4xx, because they rely on shot placement and one-shot kills, with really big and powerful bullets, and in fact if you talk to some PHs their "backup" gun in case of a charge is a pump or semi-auto shotgun with slugs loaded in it. These are folks are kill really large and dangerous animals for a living, that should tell use something.
Edit: And I think we've had this conversation before, maybe in the long gun forum, but the general consensus is - If you're within 25 yards of anything you might want to kill, a 12-gauge shotgun loaded with buck for two-legged primates, and slugs for anything bigger than a two-legged primate seems to be the best from a power-to-usability perspective.
-Rob