"Replaced from stock nozzle on a JG AU-4G (AUG ), at the same time I replaced the spring guide with a metal version with bearings. This was a ver 3 box. The combination increased my FPS by just about 25. That's 374 with .25 and 400 with .20. Please remember if your not ready to disassemble your gearbox or have never done that, then beware. This upgrade may be more then you can handle technically."