These guns are powered by an electric motor that run off of a rechargeable battery similar to those used in radio controlled cars. The motor powers a series of gears which wind and compress a spring, which in turn is connected to a piston and cylinder mechanism. When the spring is completely compressed by the motor, it is released and exerts force on the piston and cylinder mechanism. This in turn forces compressed air through a nozzle and onto a BB, which in turn is propelled out of the gun. Stock AEGs can deliver BB speeds of 240fps to 285fps using a standard 0.2g BB. Upgrading the spring, and hence the supporting gears, can easily deliver BB speeds of over 400fps or more.