Re: Canting - the right answer
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I will be convinced when 1000yd competitors start zeroing at 100yds and then applying 'perfectly vertical' holdover in order to reduce their cant errors by a factor of 10.
[/ QUOTE ]For what it's worth, a friend and I have done the following with .308 Win. match rifles after rebarreling.
First, shoot the same load we've always used for best accuracy to find out its muzzle velocity in that particular barrel.
Next, shoot the rifle prone with aperture sights; the front sight has a spirit level on it. Zero the rifle and ammo at 100 yards, then check a ballistics table/program for our atmoshperic conditions to find the bullet drop from level fire at 100 yards.
Calculate the actual bullet impact change for the rear sight movement per 0.002083-inch movement per click based on the sight radius used (varies from 32 to 38 inches depending primarily on barrel length), then adjust the rear sight down an amount equal to bullet drop plus front sight height above bore axis. Sight height's usually about 1.5 inches and bullet drop's about 1.9 inches, so move the bullet impact down 3.4 inches at 100 yards. Now the rifle's sights are set to mechanical zero; line of sight is parallel with the line of fire as the bullet leaves.
Then use a good ballistics software program to find the bullet drop at 300, 600, 800 and 1000 yards. Add sight height to those drop numbers then calculate how many clicks the rear sight needs to be raised to zero at these ranges.
How well does this work? Never been off more than two clicks (about 2/5ths MOA with a 38-inch sight radius) in elevation with several barrels. Sometimes more error in windage 'cause us humans can't dope wind that well all the time.