A new video guide for users of PolarStar Airsoft wanting to install a new FCU (Fire Control Unit) in the buffer tube of M4/M16 and similar platforms. In this case, they used an VFC HK416 for the demo. The FCU allows you to control the Rate of Fire and Burst Settings of the PolarStar Fusion Engine, and is separate from actually controlling the pressure, giving you even better control of your HPA-powered airsoft gun unlike before.