The box of ten 8g co2 cartridges are custom fit for the byrna hd.Now including 1 co2 cartridge with oil for simple maintenance every 10 co2 cartridges used.Each cartridge (new) will be good for 15-20 rounds (4 mags in a 5 round magazine) at full speed.Punctured cartridges within the byrna hd will leak over time.Size: 8 GramQuantity: 10 Per PackHazair: Yes