Set up a yard stick, or a bolder Sharpie drawn graph, at 100 yards and look at it through the optic. Take a measurement, then convert it to Mil (3.6" @ 100 yards) or MOA.
With a 2" sight offset, a 50 yard zero is almost exactly a 200 yard zero. But sight offset has to be factored to get it right.
800 Yard Steel Range
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