A common misconception about windage is that the wind speed at the target is the most important. Superficially this seems reasonable since the slower a bullet travels the more it is deflected by the wind. An M855 is deflected by a 10MPH wind by 3.6 inches between 0 and 200 yards, by an additional 4.6 inches between 200 and 400 yards, and by an additional 6.4 inches between 400 and 600 yards which adds up to 14.6 inches but the actual 600 yard deflection is 39.3 inches as shown below. Something else is going on.
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