The heck with old, in my game there are still two types of firearms that are always cased; revolvers and shotguns. Seriously, how the drek would you even LOAD a revolver with caseless ammo? As for shotguns, I suppose you could make one that would only fire slug rounds with caseless, but the entire point of shotguns is the variety of speciality rounds they can fire, and several of those would pretty much have to be cased to work, the most obvious one being shot.