Specially made and tested with close attention to tight tolerances and with clean C02, the Umarex 12-gram CO2 cartridges have uniform neck dimensions. That makes it more likely that every cartridge will pierce properly and gas will be evenly dispersed into your air gun. These are standard cartridges that work well with most 11-gram CO2-powered airguns, but are especially suited to Umarex's airguns.