Posted: 12/2/2001 7:44:37 AM EST
Based on the M193 cartridge:
Bullet deflection @ 10 mph 90 degree wind 5.56 mm /.223 55grain 0.250 ballistic coefficient 3240 f.p.s AR15 20" rifle .50 MOA windage click 100 yards 1.1" or 2 clicks x .5" 150 yards 2.6" or 3 clicks x .75" 200 yards 4.8" or 5 clicks x 1" 250 yards 7.7" or 6 clicks x 1.25" 300 yards 11.6" or 8 clicks x 1.5" 400 yards 21.9" or 11 clicks x 2" 500 yards 37.1" or 15 clicks x 2.5" 3000 f.p.s AR15 16" Carbine .65 MOA windage click 100 yards 1.2" or 2 clicks x .65" 150 yards 2.9" or 3 clicks x .975" 200 yards 5.4" or 4 clicks x 1.3" 250 yards 8.7" or 5 clicks x 1.625" 300 yards 13.0" or 7 clicks x 1.95" 400 yards 24.7" or 10 clicks x 2.6" 500 yards 41.5" or 12 clicks x 3.25" Does this look pretty accurate to you? 


See Figure F9, Example of effects of a 10mph wind, in old.ar15.com/books/FM239.pdf,
Rule of thumb for M193 Ball is 1" per mileperhour of wind at 250 meters. 10" at 10mph, etc. Been trying to battlesight a Marlin M1895G (.4570 Government) all afternoon and my mind is on larger calibers .  Chuck 

United States Offensive M4 Carbine Club.

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 AR15 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!) 


Lot of math !
In a 10mph cross wind I aim 10" into the wind at 250 meters to hit center of mass, that's about half a body width. No time to "click" anything. At 50 meters that's only 2".  Chuck 

United States Offensive M4 Carbine Club.

Could you work one of those up for me . .308 175gr Sierra BTHP Matchking bc .264. Thanks



Yeah, it is a lot of math, but not really. The idea is to think of crosswinds and angles in terms of the number ten.
Chuck, I like your system because it's efficient and easy to remember. This other system tries to undo some of the confusion of MOA and get you to think in terms of clicks. You know one basic adjustment for a 10 mph wind at a certain distance and then you can calculate for angle or windspeed. I thought of the AR for this example, but this theory can be adapted to other rifles and scopes with the help of a ballistic calculator. 


I think one of Chuck's points, although he did not say this directly, is that in battle conditions any lead you put on your target is going to be calculated in your head, by experience, not by changing the zero on your rifle. The lead/hold will be based on range, how fast your target is moving, wind, and all the angles involved. Doing the math is a good learning exercise but in the end you need to get the feel of leading by shooting. 


Battlesight vs. slow fire on the 600 yard line at Camp Perry. Two different disciplines.


United States Offensive M4 Carbine Club.

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