I forget the statistics but most gun owners own multiple guns including liberal and conservative Americans. I consider myself liberal and I have three rifles and a pistol. Most of my liberal friends have something at home.
There is this myth that all the conservatives will descend on a city and it would be like shooting fish in a barrel, as you say. But they don't figure into the equation is having to get off their lazy asses and drive, en masse to a liberal city and it's like liberal city wouldn't see a bunch of pick up trucks filled with yahoos from the country coming many miles away. Then is the population density of cities. Even though there might be more guns in conservatives hands, you can only fire one at a time and because of population density there would always be far more liberals and many have guns. Plus city warfare is hell. Just look at Ukraine. Good luck with your little civil war!