I would like to add. As your round slows down in flight the BC ever so slightly increases. To put this in to point I will use some data from the book being released soon. Take a 6.5mm 150gr BTHP round. Above 3000fps the G7BC is .303 once it falls below 3000fps it changes to .306, once it drops below 2000fps it changes to .314, below 1500fps it is at .322 and starts to curve off from there. This of course isnt a perfect fall off from point to point, but is a curve. As this BC changes, so does the effect your wind has on the round.
Now I would also point to a research article done by one of our engineers here at Applied Ballistics. You can read this article here
http://www.nvisti.com/wp-content/uploads/2014/06/NVDOC1403-Wind.pdf but it explains when, and where the wind is the most critical and how when it changes its effects change. The wind at the shooters location has the most effect on the bullets trajectory. Now as you increase in range (using the example from the article) that effect starts to level out. But if you are shooting at 200 or 1000 the wind still has around 50% of its effect from the first third of the bullets flight path.
This is a direct quote from the study "If we break each range into thirds, how much do those segments contribute to the overall effect of the wind? Figure 3 shows that breakdown: at 200m, the first third accounts for 56% of the influence, the middle contributes 33%, with the third closest to the target roughly 12%. As the distance increases to 1000m, the influence of the first third drops to 44%, the middle third increases to 39%, and the last third grows to 17%. The front portion of the trajectory obviously plays the most significant role in determining the bullet's deflection, but with increasing range, the middle section needs to be considered as well."
I would bring the formulas in to this thread, however they are in the article if you wish to give them a go! Just to complicate things a little
As the bullet slows down, the BC increases in which case the winds effect on the round changes, so at each step along the flight path (each time the fps changes) the winds effect changes, and you end up with a formula that becomes extremely complicated and long. Or you can let us do the solution for you!
One last thing to add, driving a heavier round, at a higher velocity helps to reduce the wind deflection.
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