SECOND LIFE - MAXX HOP UP PROThe Hopup Chamber ME unit is designed to accept the nozzle length from 21. 00mm to 21. 25mm, and fully compatible with most aftermarket soft and hard rubber bucking without losing FPS or dropping BBs. The Hopup Chamber ME Housing is equipped with a new CNC Delrin Locking C Clip design to hold barrel tight without wobbling and twisting, and 3 compression springs on top, at bottom and in center of housing to ensure the hopup unit is exactly centered,