The Madbull Ultimate Hop Up Chamber has many features that you won't find on any other M4/M16 hop up. For example, the integrated chamber lock system keeps all of the BBs that are inside the hop up nozzle in place even after the magazine is removed. Also, on the side of the loading nozzle is a place to mount Madbull's LED Tracer system. The LED add-on will be available soon and sold separately. With this revolutionary system you can use tracer BBs with any M4/M16 magazine. Finally, the adjustment wheel has been changed so that it's easier to adjust. Madbull has been and continues to lead the way with innovative airsoft products such as this Ultimate Hop Up.