Most long-range competitive riflemen use mirage for "doping the wind"—their jargon for estimating wind direction and speed. This isn't the kind of mirage that produces an imaginary oasis or any other nonsense. No, in reading mirage you employ an optical device—your spotting scope—to detect the way heat waves shimmer above the earth. When examined through a spotting scope, this mirage tells you wind direction and speed with great accuracy.
To see mirage, lay prone and focus your spotting scope on your distant target. Now, rotate the focus ring and you'll sec that as the target becomes blurry, the heal shimmer you may have hardly even noticed becomes very clear. Disregard the target and tune the focus for this shimmer—the mirage.
Mirage is most easily seen by focusing at a point about halfway to your target and is most distinct against a dark background. You may find that you must tip the scope down a bit closer to the earth for the best perspective.
We've illustrated four views of mirage on the facing page to show how it's affected by wind. On the left, mirage is rising straight up—u'boiling," as shooters say—which indicates no wind at all.
The easiest way to understand what hap-
A Marine Force Recon operator reads mirage in Iraq's western desert to calculate wind direction and speed.
Minimize wind effect by repositioning directly up or downwind (L) or reducing the distance (R)
Wind values, by direction
Fine-tuning wind values
Range and Wind Estima i ion
pensation correctly, you have to determine the angle of the wind, because how the wind flows across the bullet will determine the amount of drift.
As our illustration on page 356 shows, a tailwind or headwind will have no value; they have essentially no effect on a bullet's flight. A direct crosswind, which blows from the right or left 90 degrees into the path of the bullet, is called a "full" wind because the full effect of the wind is experienced.
Here, though, please pay close attention: an oblique wind of 45 degrees, from right or left, has not a one-half value but a ihree-quaners value. It has a 75-percent effect, even though the angle is only halfway between no effect and full effect.
Most shooters initially have trouble getting this straight in their heads. The effect is not proportional because of the aerodynamics of a bullet in flight. Just remember that halfway between full and zero effect is three-quarters.
As seen in the next illustration, benchrest shooters use even finer values and split the wind for exact aiming. I've included this to give you a better feel for how quickly the wind has an effcct once a bullet is other than at tail or head. Once it's just 15 degrees right or left, already a quarter of the wind value must be used when compensating.
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