Originally Posted by MontanaRifleman
The only thing is that the windage difference @ 1000 yds maybe coriolis and/or spin drift and not cant.
I doubt there's more than a 1/4th MOA error caused by coriolis and/or spin drift through 1000 yards. There's only 1/2 to 3/4 degree elevation angle above the horizontal for most cartridges to zero at 1000 yards. And the bullet's angle of fall at 1000 yards is just over 1 degree. Hardly enough to show the effects of coriolis and/or spin drift, in my opinion.
I've shot the same windage zero from 100 to 1000 yards with different 30 caliber cartridges and one 26 caliber one. I've got 100 yard zeros with new barrels then set the sights down equal to bullet drop plus sight height for mechanical elevation zero. Then made my usual come-ups for 1000 yards and windage (plus elevation) zero was good.
There's several internet sites showing that there really is a few inches of both horizontal and vertical deflection at 1000 yards caused by coriolis and/or spin drift. That's fine by me. In practical applications or even precise ones, the errors are insignificant. Us humans make more errors in judging windage corrections for cross winds than spinning bullets shot on spinning planets cause. I've shot long range in several places both above and below our planet's equator and haven't noticed any difference in windage zeros.