CNC Aluminum Hopup Chamber M4A Pro (with BB Latching System) unit is precisely machined to perform accurately and consistently on Tokyo Marui (include G&G, KRYTAC, except KWA) Standard M4/M16 AEG series. The Hopup Chamber M4A unit is built with an aluminum Rotary Dial Knob for fine hopup adjustments, the precision Hopup Lever and 4mm Bucking Nubs (6mm Bucking Nubs are optional) to perform best with R-Hop and Standard-Hop to keep the BB shooting accurately and consistently on every single shot.