For a survival rifle that fits in a (deep) backpack, a Thompson Contender carbine with a rimfire, centerfire and shotgun barrel would cover all the bases. I'd rather have a 20ga over a 410ga, even though shells weigh more or you carry less for the same weight.
For a social uprising gun, well, the Roof Koreans made good use of semi-autos and bolt actions in Los Angeles, Ferguson and other riot torn cities. Didn't even have to use them. Just having them and the social misfits knowing they had them solved the immediate problem.
There have been several videos lately where social misfits are urging other social misfits to go to the suburbs, run amok, and burn the suburbs down. Apparently they must think most suburbanites are not armed, unlike Roof Koreans. if they can manage to get to the suburbs in numbers large enough to cause problems, they'll likely be in for a big surprise.
The real problem is going to be with small but armed gangs (blunt instruments, knives, or guns) raiding individual homes in a social breakdown. Time and again we've seen flood victims on the east coast spray paint on plywood or garage doors that looters will be shot on sight. Those areas seem to have calmed down quite a bit after notice was served. Saw a lot of shotguns and .30-30's being carried. A scoped .30-30 makes a devastatingly effective anti-personal weapon, yet is "politically correct". Sure, the magazine on most holds 5 or 6 rounds, yet most overlook that those versions with loading gates can be topped off at will. I've used lever guns in tactical matches just to prove a point and topped them off between firing points. It's not the gun, it is determination and practice.