This FN factory part is called a Gas Control Screw. It screws into the barrel through the gas block. These gas control screws are more narrowly bored than standard, resulting in less gas flow and less recoil and spring buzz from the bolt assembly. It’s our experience that all FS2000s are overgassed and will benefit from this upgrade, without impacting dependability, regardless of ammo type and environment. If you do encounter a situation where more gas is needed for the weapon to cycle, please let us know, but in the short term, switching the gas plug to the adverse setting will more than counteract the reduction effect of this reducer.