Re: Scope Leveling Pointers
If you dial your come-ups, then I would suggest using the feeler gauge or similar method to verify that the scope body & turrets are square to the gun.
If you're a hold-over type, then I would use levels and a plumb line to make sure the rifle is level and the reticle is perfectly plumb.
Not all scopes have a body that is square with the reticle; many times you have to choose which you want to true-up and then live with the slight error in the other.
For example, I installed a new scope a while back and after using parallel bars (which I find are easier and more accurate for me to use than feeler gauges) to ensure that the flat bottom underneath the turret assembly on the scope was parallel to the rifle's Picatinny rail, I then leveled the gun and aimed at a plumb line outside. I had about a 0.2 mil runout of the reticle over a 5 mil drop. If I were to use dialing to primarily adjust dope, then I don't really care what the runout is since the turrets should track true to the rifle and move the center of the reticle straight up and down in relation to the rifle. However, if I don't dial and instead use hold-offs, I'll have some inherent windage error built in unless re-level the system using a plumb line. Too OCD? Probably.