Quote:
Originally Posted by obsessed1
Take the diameter of your scope tube + diameter of bolt ( on an open top type action) or action on a closed top type and divide that in half. Add in the distance between top of bolt( action) and bottom if scope tube. That is the #. This data does matter as distance increases.
As for ROT you can do it the old fashioned way using witness marks and a tight patch on a rod. Mark the rod at your "start" and your "finish" of one full rotation. Measure between marks and that's your ROT.
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This works, personally I find it a lot easier to just pull the bolt out and use a tape measure or caliper to eyeball the distance between the centre of the bolt/rear action bridge and where the crosshairs are in the scope. Being relatively close, as in within a 1/4" is plenty accurate on this measurement. If you want to see the difference in drop input a bullet, speed etc in a drop calculator with the standard 1.5" scope height most calculators have pre-input, now change the height to 2.25, which is close to what most scopes actually are.
So as an example using a 117 grain bullet doing 3200 fps, 1.5" scope height gives you 3.3 high at 100 for a 300 yard zero, 2.0" scope height gives you 2.9" high at 100 for 300 yard zero and 2.25" high gives you 2.8" high at 100 for a 300 yard zero.