The above wind card is from data obtained from a ballistic computer program. Printing it out and using it as a guide for your shooting of M193 ball ammunition is recommended. Actual wind drift is going to be different from theoretical data, obviously, but this information serves as a starting point or an educated guess if no other system is in place. Below, we will examine a system to expand upon our data and use it for differing wind speeds and angles. This system was fashioned into utility by Ed Pocock III and I've edited to be as helpful to AR-15 shooters as I could.
First determine the range and the number of clicks needed for a 10 MPH Full Value Wind. Second, multiply the percentage of wind speed, as it relates to 10 MPH. For example, 1 MPH = .1; 2 MPH = .2; 3 MPH = .3 and so on to 10 MPH, which equals 1, and up to 12 MPH, which equals 1.2. This chart should be accurate up to 12 MPH and possibly to 15 MPH. Lastly, multiply the number of remaining clicks by the Value of the wind, where a Zero Value wind equals 0; 1/4 Value equals .25; a 1/2 Value equals .5; a 3/4 Value equals .75; a 9/10 Value equals .9; and a Full Value wind equals 1. The final equation looks something like this:
CLICKS * WIND SPEED * WIND VALUE = ACTUAL ADJUSTMENT IN CLICKS
We'll apply some basic problems to the Wind Card and work our way up to some more complicated examples.
1) Your target is at 300 yards. The wind was determined to be a steady 10 MPH FULL Value Wind. If you answered "8" clicks into the wind (for the 20" rifle), you're right, since the chart is already set to this number of clicks anyway. That was easy, let's try something a little harder.
2) Your target is at 300 yards. The wind was determined to be a steady 5 MPH FULL Value Wind. To calculate the number of clicks, the equation is as follows: 8 * .5 * 1 = 4. The answer is "4" clicks into the wind.
3) Your target is at 300 yards. The wind was determined to be a steady 10 MPH 3/4 Value Wind. To calculate the number of clicks, the equation is as follows: 8 * 1 * .75 = 6. The answer is "6" clicks into the wind.
4) Your target is at 300 yards. The wind was determined to be a steady 12 MPH 9/10ths Value Wind. To calculate the number of clicks, the equation is as follows: 8 * 1.2 * .9 = 8.64. The answer is "9" clicks into the wind. Even here, a finer adjustment can be made with the remaining .64. Instead of just rounding up, consider how the wind was acting. If it seemed more like a Full Value, round up. If it seemed a little less severe than a 9/10ths value wind, but not of a 3/4 Value, then round down to "8".
It's the Actual Adjustment in Clicks that gets dialed into your sights. Remember to click INTO the wind (we've all turned the knobs the wrong way!)