This Colt M4A1 rifle is having the GHK Gas Blowback system as the shooting engine. It is equipped with Nylon Fiber receiver to reduce the rifle weight and high grade Aluminum tactical rail to install accessories. This rifle is an official licensed product with full trademarks and logo (licensed from Cybergun). Green gas is recommended to be used on this GBB. Package comes with a 40 rounds magazine. This rifle GBB system can be interchange with KA M4 AEG gearbox so user can enjoy the GBB and AEG experience from the same rifle.