If you shoot into a head-wind, does the bullet slow appreciably and thus strike lower on the target? Well, not unless the head-wind is of hurricane strength and the target is very far off. Fired into still air, a .270 bullet meets a force equal to that imposed on a stationary object by a 2,000-mph gale. A 20-mph breeze is pretty strong, but it adds (or, in the case of a tail-wind, subtracts) just 1 percent to (or from) existing drag. Any resulting vertical displacement of the bullet is very hard to see.
But wind does move bullets vertically â€“ with a little help from spin induced by the rifling. A right-hand twist will give the bullet â€śspin-driftâ€ť to 10 oâ€™clock in wind that drives from 3 to 9 oâ€™clock. That same twist will depress the point of impact in wind moving from 9 to 3 oâ€™clock â€“ youâ€™ll get a 4-oâ€™clock strike. Reverse that rule for left-twist rifling. Vertical shift is of no account when youâ€™re firing a hunting rifle at big game over normal shooting ranges. But itâ€™s a factor at long range when the X-ring or prairie dogâ€™s noggin is tiny even at top-most magnification.
Accomplished marksman David Tubb has researched this phenomenon and come up with a scope reticle calibrated not only to accommodate normal drop and drift, but also spin-drift. The reticleâ€™s horizontal lines appear on a slant, tracking the actual path of the bullet, not the direction of the wind. Iâ€™ve used it; it works!