With the high-quality M4 gas blowback rifles from the Viper Tech which match the Inokatsu ones, come a high quality CO2 magazine which can be used with these GBB-Rs. This magazine can take in 12g CO2 Cartridge but there's no mention of the magazine capacity. This can only be used for the Viper Tech AR-15 & SR-15/16 GBB series only and costs US$64.26 each at CWI Airsoft.