Understanding the wind
Reading and understanding how the wind affects your bullets separates the amateurs from the experts. After reading this page, you will understand how the wind affects your bullet and how to find the error in your wind call. This will help increase your hit probability, making you a better shooter.
Before we jump into the math, you need some information. You will need your D.O.P.E. out to 800 yards. The data needs to have been trued and confirmed to be accurate. You will also need your wind value per 1 mph. I can't help you with your D.O.P.E., but if you don't have your values for 1 mph, don't worry. I'll show you how to get that information.
Use your preferred ballistic calculator to get the wind value per 1 mph. For this to work, you will need a readout in 1/100 (.00). Make sure to turn off spin drift and coriolis. You do not want these on as they will give you an incorrect value. Next, set a full value wind (90°) for 10 mph. Ex. At 500 yards with a 10 mph full value wind, my correction is .8 mils. For a 1 mph wind, move the decimal over 1 place to the left. My .8 Mils for 10 mph will now read .08 for a 1mph wind at 500 yards. The last step is building your 1 mph wind chart to 800 yards.
Let's jump in!
Ex. I
11" target @ 610 yards with 6 - 8 mph full value wind
11 x 27.77 / .5 = 610 yards
If we Mil our target, we'll see our target size is .5 mils. Next, we need to get our wind correction for our minimum and maximum wind. Looking at the chart, we can see a 1 mph wind at 600 yards is .1 mils.
.1 x 6 mph = .6
.1 x 8 mph = .8
Our wind hold will be between .6 and .8 mils.
The following formula is to get our target size in mph. This formula tells us how much wind it will take to push our bullet the entire width of our target.
Size of target in Mils / 1 mph wind effect
The size of our target is .5 Mils at 610 yards
Our 1 mph wind value is .1 mils
.5 / .1 = 5 mph
Our target size in mph is 5.
Because we have a 5 mph target and our wind call error is .2 mils (the difference between .6 and .8 Mils), we have an extremely high probability of impacting our target.
Let's add another element to this equation.
We'll say our wind is from 1:00
The cosine for 1:00 wind is .5
This means we have a half value wind. Let's look at the math.
At 600 yards with a full value wind of 6 to 8 mph
Our correction is .6 - .8 mils. To get our wind angle correction, we need to multiply by our cosine of .5
.6 x .5 = .3 mils
.8 x .5 = .4 mils
We went from .2 mils to .1 mils, further increasing our hit probability.
Because our target is .5 mils wide, our wind error is .1 mils, and we have less wind than what is needed to push our bullet the entire width of our target, we can almost guarantee impact.
Ex. II
8" target at 740 yards with a 5 - 15 mph full value wind
8 x 27.77 / .3 = 740 yards
We'll start by looking at our chart. We can see that at 700 yards, we have a 1 mph correction of .12 Mils; at 800 yards, our correction is .14 Mils. 740 yards is very close to halfway, so we'll say at 740, our 1 mph correction is .13 Mils
We multiply our 1 mph correction by our wind speed to find our minimum and maximum wind correction.
.13 x 5 = .65 Mils
.13 x 15 = 1.95 Mils
Our wind correction will be between .65 Mils and 1.95 Mils
Our difference is 1.3 Mils
To find our target size in mph, we will divide our target size in Mils by our 1 mph correction.
.3 / .13 = 2.3 mph
Our wind is between 5 and 15 mph. This is well over our 2.3 mph target size. Our target size is .3 mils wide, and the difference in our wind correction is 1.3 mils with a total error of 1 Mil. We have a high probability of a miss. We must pay close attention to the changing wind to make this shot. We should wait until the wind dies down to its minimum or is at its maximum before we fire to increase our hit probability. We can also float our reticle between .65 Mils and 1.95 Mils as the wind picks up and dies down to try and make an impact. At the range on a steel target, absolutely take the shot. Call your shot and estimated wind speed, and write it in your dope book. Mark down your impact. If you missed, run the calculations and see what the wind was doing and why you missed. Now is the best time to learn. If this shot were on an animal, I would definitely not take it.
The Overwatch
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