Years ago when I owned a 22-250 and I wanted to zero it in, looking at various books I read that all bullets cross the path of your eye twice. I forget now what the 22-250 was with a55 grain bullet but I believe it was 27 yards and 104 yards.
So as Stan stated if the gun is a bolt action remove the bolt and set a target at 27 yards and with the rifle rested look through the bore to set the rifle to hit the target then look through the scope.
Again if I am not mistaken a chuck at 400 yards aiming at his head the bullet would drop 4" at 3810 fps.
That exact distance has to do with the measurement that the exit pupil of the scope is above the centerline of the bore, among other things. I always liked to keep my scopes as low as possible. "See-thru" rings, and other very high rings, exaggerate the numbers and caused me more problems than they were worth. JMO, OMV.
