Well thing is, I also own a javelin m4 RIS, and have never taken it apart. However, in this video, NCman talks about the tube and doesnt even mention anything about the castle nut.... He just takes the screw out. I though all m4/ar15 stocks were similar.... so what would you guys do if you were in my shoes right now?
YouTube - ‪Javelin Airsoft Works M4A1 Internal Review‬‏ Go to 4:45