The M4A3 (W) 76mm we have in AH, the M10, and the M18 all fire the exact same ammo. Think of it as the difference between a Browning, Winchester, and Remington 12 gauge shotgun. Different brands, different mechanisms, same ammo.
As far comparative fire power goes, those AFV's have for all practical purposes the same firepower as the German Panzer IV H and StuG III/IV. Obviously, they lag behind the Panther, Tiger, and Firefly.