After sighting in my scope, I did some calculations that show the actual cant of my scope/base is 7 moa, not 20 moa. I'm kind of surprised because I bought what I think are quality parts: Farrell 20 moa base, SWFA SS rings, SWFA SS 3-9x42 scope.

Some background info: Rifle is a new Savage 116 FCSS Weather Warrior, .30-06. Base is a Ken Farrell standard aluminum Savage round top long action 20 moa base (whew!). Rings are SWFA SS standard low rings. Scope is SWFA SS 3-9x42. I used the Wheeler Engineering scope alignment rods to confirm the rings were aligned after mounting to base. I tightened all base/ring screws to Farrell recommended torque specs. I penciled in witness marks on the scope and verified that the scope did not slip in the rings while firing. I measured the scope centerline height to be about 2 inches (5.08 cm) above the bore centerline.

I used a laser rangefinder to range the target at 88 meters (8800 cm). Ammo was Federal Vital-Shok .30-06 with Barnes TSX 180 grain bullets, specced at 2700 fps muzzle velocity (did not verify with chrono). A ballistic calculator (Ballistic FTE iPhone app) calculates the bullet drop at 5.842 cm down from barrel bore centerline. Bullet impacts were 6.35 cm above point of aim.

When I do the calculations, I find the actual angle between scope centerline and barrel centerline is 6.7 minutes of angle. I was expecting 20 moa, since that's the base I ordered and installed. If the angle really was 20 moa, I calculate the bullet impacts should have been 40 cm (16 inches) above point of aim. With the effect of muzzle rise, I expect the actual point of impact to be even more than 40 cm above point of aim.

First of all, are my calculations above reasonable? If so, is a 13 moa total error (receiver top, base, rings, scope) normal?

I realize this doesn't matter much in practice. I'm just curious to know if this is within expected tolerances. I'm also wondering if I might get closer to the actual 20 moa angle if I undo then redo the base/ring/scope mount.