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Old April 22, 2013, 05:40 PM   #13
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 4,907
I have used Sierra Bullets' old software to calculate sight settings based on a zero at 100 yards and the come ups for 600, 800 and 1000 yards. Muzzle velocity was know from chronograph data and the atmospheric conditions noted for both when zeros were established as well as when chronographing. Done this for 190's and 155's in a .308 Win. case in each of two different rifles.

Zeros were established for "mechanical zeros" meaning the sights would be set to match a "shooting boresight" for an target at infinity. Shooting prone a 100 yards, the sight settings for a zero were logged then calculated bullet drop and front sight aperture height above bore center were subtracted and the rear sight lowered such to move the group center down that far. Actual sight radius and thread counts on the sight lead screws were known to use in the calculations. The resulting sight setting was the "mechancal zero" and was the reference for sight settings at the longer ranges.

Using Sierra's software and the atmospheric conditions at the range, come ups were calculated for each bullet and rifle combination. At all three ranges, the actual sight settings for a zero at them was within 1/4 MOA of what was calculated. Sierra's software, in my opinion, was right on the money.
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