Pertaining to my experience only here in CO. With many overnights deep in the backcountry, I have not ACTUALLY had a confrontational situation with any predators, luckily. However, I have seen more than enough fresh moose and bear tracks/scat around my tent. Here is the knowledge of my area though, lol. I do tie my food up at night and away from camp.
Mountain Lion-highly elusive, but if one gets you, they will ambush you and you won't see it coming, knife or stick better than a gun in most situations. News stories with witnesses present usually say ambush attack from behind for mountain lions (unless protecting a kill).
Bear-(luckily only black bear here in CO)-will fuck your shit up when you have food with you, tent/car/etc. Normally when confronted by a human that they didn't expect, they take off, Friends/Family with multiple personal stories on that. However, if you're sleeping and one tries to get in your tent, a gun would be a great tool to have.
Moose-Extremely aggressive especially around their young. Will stand ground and attack. BIGGER than black bear or mountain lion. They are very use to people around here and don't give a shit.
Wolves-Wolf sightings are increasing here. A personal friend of mine was surrounded by a pack two years ago. The wolves were coming after her dogs. I think a gun would certainly help here. They weren't moving fast, but were closing in and howling crazy.
A perfect gun for what you want may be a Taurus Judge.