The Reffye mitrailleuse used a 13 mm (.512 inch) centerfire cartridge, designed by Gaupillat, which represented the state of the art in ammunition design at the time. It was rather similar to an elongated modern shotgun shell: centerfire with a rimmed brass head and a dark blue hardened cardboard body. The , 13 mm (0.512 inch) patched bullet was propelled by 185 grains (12 grams) of compressed black powder at a muzzle velocity of , three and a half times more powerful than Chassepot or Dreyse rifle ammunition. This was, by far, the most potent rifle caliber ammunition in existence at the time. The Montigny and Reffye mitrailleuse systems were not designed to function with paper cartridges such as the 11 mm Chassepot combustible paper cartridge.