Between relays at Darrell Holland’s shooting school, riflemen discuss wind that swirls about the Oregon hills—a challenge at ranges from 300 to 800 yards.
Shooting rimfires at prairie dogs, you can hold center to a 75-yard point-blank range in a light breeze. Its effect on your position can trump its effect on the bullet!
Wind-Cheating Strategies: Reading the leaves, catching the drift, & reading the mirage.
He knew better. “I zeroed at 300,” he conceded. “Shot right over.” No surprise there. Most places, you’ll not often fire beyond the point-blank range of a big-game rifle zeroed at 200 yards. Given that sight setting, most modern loads will plant bullets 2 to 3 inches high at 100 yards and about that low between 250 and 280 yards. In vitals the size of a soccer ball or bigger, a couple of inches won’t matter. A long zero, or holding high to compensate for drop you’ve already factored in, can cause a mid-range miss.
Likewise, wind drift can be largely ignored inside 250 yards. A 180-grain Nosler Partition from a .30-06 sidesteps about 3 inches at 200 yards under the press of a 10-mph crosswind. A 10-mph blow not only makes leaves flutter, but it also bends light limbs. It won’t take your hat off, but if you throw it aloft, you’ll see that hat carried. Mostly, you’ll be shooting in less active air. Also, wind that comes from angles other than 90 degrees will move the bullet less. Compensating too much for wind can cause a miss.
Reading The Leaves
My best lessons in wind drift came in small-bore matches. A .22 LR Match bullet is very wind-sensitive. It starts at only about 1,000 fps, or just under the speed of sound. It’s not an aerodynamic bullet, compared to the sleek, jacketed boat-tail spitzers we hurl three times as fast at big game. Wind that would hardly move a .30-bore soft point can shove a .22 bullet across several scoring rings at 100 yards. I learned to mind not only the wind, but mirage, which showed air currents I didn’t feel, and that flags and “windicators” (fans with tails delicately mounted to swing on ball bearings) didn’t pick up. I learned that, because bullets spin, drift has a vertical component. A right-hand twist typically tugs bullets to 10 o’clock when they’re pushed from the right, and to 4 o’clock when nudged from the left.
I learned that wind from 12 and 6 o’clock has essentially no effect on bullets unless it is unusually strong. A bullet meets terrific resistance even in still air. Its own speed generates a fierce headwind and a great deal of friction on its ogive and shank. A bullet fired at 3,000 fps from a 7mm Magnum must drive through a 2,000-mph gale! A 10-mph head- or tailwind has an insignificant effect on such speed and friction. By the way, a bullet of ordinary construction leaves the barrel in line with the bore and stays that way as it drops. Unlike an arrow, it does not “porpoise.” The effects of head- and tailwinds are thus hard to state categorically, because a bullet in flight may get different pressures on upper and lower surfaces.
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by Clair Rees / Oct 15, 2013