Any reason why you don't want to just shoot it, see where it hits, and adjust from there? It doesn't really matter where it is, it will be off either way.
If it matters that much though you can turn the dial all the way to one side, then measure the distance to turn all the way to the other side, then put it in the middle... it's just extra steps though.
Wanted: 50 Beowulf Brass, .500 cal bullets
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