I use a 20x Leupold for load development so I can use a 1/4" dot or square...on ANY/ALL rifles then switch to whatever power fits what I hunt.
I think you are doing more work than required with trying to use the scope adjustments to do a drop chart. Just sight in "0" at 100 yds, shoot some targets at whatever longer range you want and measure the drop, then use any drop program to calculate the midranges. "Ibendoon" it this way for about a million years. It is simple, quick and works for hunting applications.
I have very accurate rifles(or they don't last in my rack) so once sighted at 100 yds, it only takes one or two rounds at 200, 300, 400 etc to find the drops, then input the data into a software program or an online program for the intermediate ranges. Sometimes I do it the other way around...use chrono and BC data and 100 yrd target, input that data into the drop program, THEN check the drop chart at actual distances to see how close the data actually is. Most of the time it is pretty close if the bullet BC and chrono data is anywhere true.
And as Larry said, most scopes aren't installed perfectly square and perpendicular to the bore line so unless you have a super accurate rifle, high dollar perfect scope, you won't know how much off the scope is.
Open sights and human eyes are not very good for ranges beyond 100 yds...remember a 0.005" movement off targer is equal to 1" at 100 yds, 2" at 200 yds, etc.
Use a bench and sand bags, or a lead sled if you have one, to eliminate the wiggles.
Luck