Seriously, the survivor’s .223 carbine is amazingly powerful. In general, I prefer single shot rifles since I don’t like wasting bullet, and each shot does high damage. At around 4-5 tiles away, it’s pretty much instant death to most zombies. Even brutes. Can even manage to kill a hulk in 4-5 shots.
Case in point, encountered a big horde. Had enough ammo so I set out to shoot them. Killed about 100-plus, and none of them got near enough to damage me, not counting corrosives spitting out acid which didn’t do damage. For most part, I waited for the zombies to reach around 10 tiles away, and start shooting, and back away when they got too near. It was enough to get my rifles skill up to 11.