PolarStar JACK HPA Conversion Kit for M4/M16 Airsoft Guns Designed, manufactured and built in the U.S.A., Assembled from CNC machined aluminum components with high performance delrin nozzle. Universal cylinder design is compatible with numerous gearbox versions., Optimized flow profile, firing point and flow path promotes superior shot consistency and accuracy. Capable of functioning in damp and sub-freezing climates without affecting performance or reliability., User selectable Semi/Full Auto, Semi Auto Only and Variable Burst modes. Independently adjustable velocity and cyclic rate., Auto Switch mode allows for proper selector configuration for specific models. Easy to use Fire Control Unit (FCU) with LCD display and five position joystick., Instantaneous trigger response. Faster than an AEG with a Li-po!