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.
