I think its possible to have a number of rifles chambered for the same cartridge without them being redundant, since each rifle is acquired for a specific purpose. Lets consider the .308 Winchester cartridge. Prior to the ban, one could own a military style semi-auto rifle chambered for .308, or post ban a Garand, an FN-49 or similar rifle which would be useful in service rifle competitions, personal defense, and so on. A .308 target rifle could be used in competition like F class, for varminting, and long range shooting. A light weight carbine chambered for .308 is a dandy deer rifle, and might well be the go to rifle of the rural household for problems that can only be solved with gun fire.