I ran into a similar problem as you have. I thought I needed a 20MOA base on my long range gun, only to find that I did not have enough adjustment (In three scopes) to zero the gun at 100 yards. I used the med zee weaver rings, and found that if I placed the +20 (Back bottom) and the -20 inserts (front bottom) it put me close to 0 MOA. I was then able to zero the gun in at 100 yards. I still have enough adjustment to go out way past 1000 yards, with either of two scope. (Weaver t36 or Vortex Crossfire.)