In the last 2 days, I have been asked about how I make my wind calls. I figured I would pass this info on. Shooters sometimes look at me puzzled when I tell them I would rather shoot in a full value wind than a head or tail wind, or a wind that is variable from the front or rear. Why? Because I can "calculate" the full value wind much better than I can predict the changes in wind from the front or rear. So, here's how I do it.
Take the ol' trusty 6.5 Creemoor that everyone has now. We are shooting a 140 grain ELD-M at 2750 fps with a G7 BC of .326. Below is a drop chart and wind value of this bullet in mils. (For moa, you do the exact same thing, just use moa) I run all my wind charts in 1 mph increments to be more precise, and keep the math easier and simple. I analyze the shooting range and calculate my wind at 8 mph coming from my 2 o'clock position. My target is 500 yards away. Looking at the drop chart, I see my 1 mph wind value is .08 mils. So, .08 times 8 mph is .64 mils for a full value 3 o'clock or 9 o'clock wind. My wind is coming from the 2 o'clock, so I take 87% value of the .64 mils, which would be .55 mils (.64 times .87). Now, .55 is half way between .5 and .6, so I would hold .5 mil and make any slight adjustment on my second shot, if needed. But either way, I'm going to be near dead on for my wind call.
(My fast math method- .08 x 8mph = .64; 10% of .64 is .06; .06 minus .64 is .57 mils)
Let's do another one. Target is 700 yards away in a 14 mph wind coming from the 7:30 position. 1 mph wind drift is .12 mils. .12 times 14 mph is 1.68 mils (this is a full value wind). Wind out of the 7:30 position takes 70% of the full value wind, so 1.68 times .70 is 1.17. I would round up and hold 1.2 mils into the wind.
(My fast math method- .10 x 14mph = 1.4, plus .02 x 14 mph = .28 (round up to .3), for 1.7 mils full value. 30% off is about 1.2 mils)
This is the exact system I use for my wind calculations. Once I learned the "clock" system, I went from guessing my wind to actually "calculating" my wind. My first round impacts became much more common. The fast math method is how my brain often works in computing the wind quickly in my head. Often times my quick calculations are easily within less than .1 of the actual calculated wind. I break down the figures in tenths most of the time in my head and can calculate it quickly. But that's just me. You may think or do math differently to get to the same amount, but do what works for you!
What's easy about it is, you really only need to remember 3 values-
.5 or half value at 1 o'clock
.7 or 71% value at 1:30
.87 or 87% at 2:30
From there, it's the same all the way around the clock system, depending on which angle the wind is coming from. This is how I calculate my wind. It's simple and fast to run. And yes, I often have a calculator on me if I feel like I need to compute it. Often times I'll round up the .87 to .9, and calculate a 10% less in my head, and run that if the wind isn't blowing much. It will certainly get you close enough on target to make a hit.
Range Elev Wind
(yards) (mil) (mil)
0 --- 1 mph
100 0 0.01
200 -0.44 0.03
300 -1.12 0.05
400 -1.91 0.06
500 -2.78 0.08
600 -3.74 0.1
700 -4.79 0.12
800 -5.93 0.14