Product Features: (1) Gearbox V.2 for Class Army or Marui gun body. (Prefer metal body.) (2) Steel trigger + Steel charging handle. (3) Default velocity: 300ft/sec (Upgradeable) (4) Blow back single shot action. (Just like paintball gun's action.) (5) Semi auto (Upgradeable) (electronic trigger under development.) (6) 12g CO2 cylinder in your grip. (~70-80 shots depend on pressure/ temp.) (7) Optional: external CO2 adapter/ quick connector.