[Mauzen]

You would have to rewrite the ammo system. Just give the player one full clip at once, store the real total ammo in a variable. Everytime the player reloads (make a callback with GetPlayerWeaponState) give him a full clip, and decrease the ammo variable. You could use e.g. a TextDraw to show the ammo left.
Cant think of another way to do this atm.