Mechlabs brings you the Nexxus series engine for the M4/AR15 platform. The Nexxus is a full mechanical engine capable of firing in Semi-Automatic and Full automatic with flip of the selector. No need for batteries just hook up your HPA tank and you are ready to rock. It also boasts an Ultra Fast trigger pull and is very efficient on air up to 3000+ shots with a full 48/4500 tank. The Nexxus engine comes ready to attach to your external HPA regulator set up but if you'd like to run a shoulder stock tank we have a kit that has a regulator built in. Jump on board the HPA revolution with Mechlabs!