Our box of ten CO2 cartridges are custom fit for the Byrna HD/SD & EP. 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.
It is recommended to swap out punctured CO2 cartridges and leave an un-punctured cartridge inside the Byrna HD/SD & EP to avoid any compressed air loss. The Byrna will puncture and fire the first round at the same time.