Currently using guns as a primary weapon is can get prohibitively expensive in either parts or ammo. An unbreakable gun that uses the cheap .22 ammo and can accept a silencer could make it viable to shoot your way through the apocalypse. The slow rate of fire and a small magazine would keep the weapon balanced by leaving the player vulnerable to hordes and feral packs. Similar in function to the Echo S2 from Heartland.
In SOD1 there was the 983 Squirrel bolt action .22. Maybe that could make a comeback.