If your having problems shooting right or left of poi play with the cast off shims they supply w gun. Screw in full choke. Set up target with baseball sized dot at 15 yds. Snap gun to shoulder and shoot at dot as instinctually shooting. That will tell you what adjustments need to be made. Should be able to make adjustments to gun to obliterate dot. Worked w my m2 years ago . I too required the c drop shim to obliterate that dot and right hand cast shim.