Posted: 6/25/2015 7:37:09 PM EDT
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Below is based off of .308 175 grain pushing 2650 FPS
Over the years I've used just about every formula for dialing wind than you can imagine. In the Marine Corp we used the following formula: Range (in 100ths) x Wind (in MPH) divided by the range constant = Minutes of full value wind Our Constants were the following: Yards 1000 - 10 900 - 10.5 800 - 11 700 - 11.5 600 - 12 500 - 12.5 400 - 13 300 - 13.5 200 - 14 So if you had a target at 400 yards and the wind was 8 mph. You would take 4 x 8 = 32 divided by 13 = 2.46 MOA In the real world having a calculator in hand isn't realistic. I started using this formula and it's easy to remember and can be done in your head. Wind (in mph) x constant = Minutes of full value wind Yards 1000 - 1 900 - .8 800 - .7 700 - .6 600 - .5 500 - .4 400 - .3 300 - .2 200 - .1 Same problem as above .3 x 8 = 2.4 MOA This formula is accurate to 16th of an MOA. (99.9% of the time) If it's half value, divide the answer in half. Quarter value, three quarter value... divide appropriately. If your working with Mils, divide by 3.438 I've used this formula all over the world. It works for me. |
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Yeah, wind charts and my formulas are all Full Value Winds. Meaning directional winds blowing from 3-9 or 9-3 o'clock. If you have winds from 1:30, 4:30, 7:30 or 10:30, those would be half value. So wind would affect the projectile half of what a full value wind would. If you come up with a shooting solution of 3 MOA of wind, and the wind is blowing over your right shoulder from 4:30, add 1.5 MOA.
1/4 value wind for 2 MOA would be a 1/2 Minute. 1/2 value wind for 2 MOA would be a 1 Minute. 3/4 value wind for 2 MOA would be a 1.5 Minutes. No value winds (12-6 or 6-12 o'clock directions) can affect your projectile, meaning a right hand twist with a head wind at distances of 800 yards or more, can cause the projectile to hit high and right. Tail wind, low and right. (Left hand twist same high and low, just impacts left) A lot of shooters make the mistake of calling wind direction and speed off of range flags (10 feet in the air) and at their shooting position. A lot of times, that's all you can do. However, look at the trajectory of your projectile and how high above line of site it goes. Why? Because wind goes in layers, also trees and hills will act as a wind barrier to either reduce the velocity, block it, or in many cases, redirect the wind and cause velocity and direction changes. I usually make my wind call 3/4's of the way down range. (500 yards, .308 only goes approximately 5-6 feet above line of site. Flagpole is at ten feet, and there's a hill 8 feet high blocking the wind) Bottom line is, every time I go shooting, the wind will humble me as a shooter. A lot of times shooters make correct wind calls but wait to long to fire. By the time they shoot, conditions have changed. "No value" winds will humble you as well because they often times turn into 1/4 or 1/8 value winds with little or no warning. Or worse yet they turn into fishtail winds. (Blowing left and right) I'm lucky I live and shoot at Tiger Valley. We average 17 MPH winds here. I get a lot of chances to practice "calling" wind shots. Every time I make a shot, I ask myself three things; "Did I hit the target? Do I need to shoot again? What do I need to do to hit it?" |