Over the past year or two, I've had many people from the forum PM or email me about wind reading. I started working on a decent reply, something more lengthy than, "watch the grass and trees!" about a year ago, but I wasn't satisfied with it until some recent reading helped clarify what I do, and helped me formulate a better reply. Here is that extended article. Any errors are mine. Before we start, I should point out the Jeff Hoffman of Black Hills Ammunition developed the actual formula and deserves credit for it.
The Big Mystery
Reading the Wind and Successful LongRange Shooting
Since beginning my long range shooting career, I have found that there are really only a few significant variables in successful shooting. Unfortunately, those variables are sometimes hard to define, and sometimes even harder to control.
My journey has led me to realize that the largest obstacle to successful long range shooting is my ability to read the wind.
A bullet fired from a rifle moves in three dimensions; longitudinally (from you to the target), laterally, (the effect of the wind), and vertically (the effect of gravity). Since you have fired the bullet, we’ll assume that you have controlled the longitudinal travel to the best of your ability. Since gravity always is in place, and with very few exceptions always has the same force on an object, (remember the Leaning Tower of Pisa and Galileo from grade school?) we’ll assume that you have correctly compensated for the drop of the bullet.
That leaves us with lateral movement, or the effect that wind will have on your bullet.
Over the years I have read dozens, if not hundreds, of articles on windreading, and I’ve learned tremendous amounts about if from listening to masters like Gene Econ, Monte Milanuk, and Paul Scott. I’ve made the take home reading from this paper in an italicized font, so you can discard all the rest if you like and just read the take home points!
The first thing I learned was to estimate the wind speed by watching natural wind gauges. Watch the movement of trees and grass.
Figure the wind to be 1 to 3 miles per hour if smoke moves laterally, approximately two to four miles per hour if the long grass moves occasionally, approximatelyf ive to nine miles per hour if the grass leans and smaller tree limbs move, approximately 10 to 14 miles per hour if thicker tree limbs move and 15 to 20 miles per hour if trees sway and the grass constantly moves.
Those are great approximate indicators, but they only are part of the story. Wind direction is the other factor. It’s easy to calculate wind effect if it is at 90 degrees from your bullets line of flight, but what about if its 45 degrees, or 30 degrees?
A 90 degree wind is a full value wind, meaning that it will affect your bulletmore than any other, so if you know that there is a 10 MPH wind at 90 degrees affecting your .308 bullet, you will know it drifts less than an inch at 100yards, 22 inches at 500 yards, and almost 10 FEET at 1000 yards.
But what about winds that aren’t directly perpendicular, how do you calculate those?
Fancy calculators, cell phones, and ballistics programs will do it; put in good data, and they’ll pop it right out, but those are difficult to handle in the field, take time, and are expensive. Isn’t there a cheaper way?
Fortunately, there is, and with a little practice, you can master it. (Hey, I didn’t say itwas going to be easy! Shoot more, and practice this while you do it!) So here you go!
There are just a few things you need to memorize, and a few things you can calculate in your head, and 3 Basic Steps:
1. Make you initial range calculation in hundreds of yards, and subtract 1.
2. Adjust for actual wind speed.
3. Adjust for actual wind value.
See, I said it was basic, right?
To accurately compensate for wind speed, you have to KNOW wind speed. You can use that information I gave you earlier to approximate it, and plug one of those numbers in, or you can get accurate numbers by buying a Kestrel or similar anemometer. (That’s the fancy word for a wind speed gauge! See you even get some vocabulary education on the Grendel Forum!) You can buy these for less than 100 bucks now, so it’s really a little piece of what shooting costs. I like Skywatch anemometers (made by JDC) because they are omnidirectional and you don’t have to worry that you are perfectly facing the wind to get a good reading, but Kestrel and other unidirectional wind meters work fine with a little more effort on your part.
Practicing with your anemometer and judging wind speed will allow you to develop a more accurate wind estimation than the general information I gave you above, and you will soon find you are within a mile or two of actual wind speed without having to look at the gauge. That’s a big step, because it speeds up the process!
Then determine wind value:
90 degrees is full value
65 degrees is 9/10 value
45 degrees is ¾ value.
30 degrees is ½ value
15 degrees is ¼ value
Lots of references will say that a 45 degree wind is half value, but we’ve compensated a little for that with the initial range compensation figure (subtracting one from the actual range) and these numbers work more effectively. (Trust me here! It works!)