An FCU (Fire Control Unit) is needed for all Polarstar rifles with the acception of the Polarstar Kythera whether its the standard Polarstar FCU or a Gorilla FCU. The Gorilla FCU gives you the ability to change the setting of your HPA rifle on the fly via a mobile app and blue tooth. The app offers unlimited presets for any rifle so you can plug this into a CQB rifle and load one tune, then plug it into a DMR and load a different tune. If buying this with a Polarstar rifle from the airsoftUS it will come pre tuned for that specific rifle. If your buying this as a solo product and you would like it tuned for your rifle please fill out the contact form or leave a comment giving the following details, the more specific the better
Which Polarstar Engine - Ex. Polarstar Jack
Hopup unit ------------- Ex. Maxx me pro M4A
Bucking ---------------- Ex. Maple leaf macron 70 degree
