The "Support_AmmoGuns" script included in various mods (Bushido's tiered set, TF2 basic guns, .880 Rifle) supports weapons having a limited clip size and reload functions but doesn't use any physical 'item'. It has to be implemented into every specific weapon using it with image states rather than some general one like Rotondo's zombies ammo mod as it would probably break any kind of special weapon or ones with alternate firing. (e.g. spread machine guns)