Retro Arms CNC Hop Chamber AR15 ULTRAIntroducing the Retro Hop Chamber in final form, the Pinnacle of Retro Arm's Hop up chamber line for AR Style Airsoft Replicas. Retro has their Basic, Pro, and now the Ultra. Each hop chamber has an increase in modularity and tun ability. The ultra is for those craving perfection with completely modularity. The Retro Arm CNC Hop Chamber Ultra has an adjustable feeding shaft as well as an adjustable Nozzle shaft. This is a key feature when fine tuning