Even chronograph data can be wrong. I don't know how many times I've input Chrono average velocity, ballistic coefficient, and environmental data. Get a calculated trajectory correcetion, shoot it, and it's wrong. A couple tents Mil at 500 is actually quite a bit, it only gets worse the farther out you go. I'm not in the business of close enough. Shoot it, write down "level", .1 or .2 Mil high or low, run it out as far as you can, then go back into the ballistic calculator and adjust MV or BC until calculated data matches what you just shot on the range. Now you have true D.O.P.E. Data On Previous Engagement. If you saw my post, you saw what I wrote down in the little spiral notebook as true DOPE. That was not calculated data, that what what I just shot on the range. There is a difference.
Chronographs get you in the ballpark. Nothing is a substitute for actually shooting the rifle/ scope/ ammo combination on the range.
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