CNC Aluminum Hop-Up 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 Hop-Up Chamber M4A unit is built with an aluminum Rotary Dial Knob for fine Hop-Up adjustments, the precision Hop-Up 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.
The Hop-Up Chamber M4A unit is designed to accept 21.00mm to 21.25mm nozzle length, and fully compatible with most aftermarket soft and hard rubber buckings without losing FPS or dropping BB during use.
The Hop-Up Chamber M4A unit is wisely equipped with an interchangeable Inlet Adaptor OD11mm to ensure the Hop-Up unit is inserted exactly in the center of the 11mm inner bore AEG Gearbox/HPA Engine nozzle outlet without wobbling. (Inlet Adaptor OD11.5mm and OD12mm are optional)
Also mounted the removable CNC Brass Side Wings to slide smoothly into the outer barrel slots, and included an advanced CNC Delrin Locking C-Clip to hold the inner barrel tight in place without wobbling and twisting.
More than that, the Hop-Up Chamber M4A Pro unit is specially designed with a new BB Latching System to prevent BB dropping after removing the magazine. The Latching Arm can also be manually pressed to release the remaining BB from inside the Hop-Up chamber.

Rossi M4 MOE Style Compact Stock