@ White_knight, sorry to tell you this, but NPAS definitely sucks on the KJW's M4. The only way to go is Cradle Velocity Reducer kit, as the RA-TECH adjusting screw will most likely bend and eventually break within only a few shots.
Installed two of these for a customer, and after only 3-5 shots, after having 50fps inconsistency, I took it out to see that it was already bent... I had to shim the screw so it was seating on both side so I could not see the tiny screw. Thus the fps couldn't be adjusted, unless you thin or thick the spacer...