1 MPH Wind value and Target Size in Wind

I've launched Season 2 of Into The Wind, my YouTube series on long-range shooting. Watch it at https://www.youtube.com/@theoverwatch23-10. I just wrapped up Episode 6, where I break down several formulas. In this blog, I'll discuss four formulas, including how to calculate the 1 MPH wind value and target size in wind. Let's tackle the 1 MPH wind value first.

Knowing your 1 MPH wind value gives you a quick, accurate way to calculate wind. To find your 1 MPH value, first collect the following information.

Distance - 600 yards

Gun Number - 4

Wind Speed - 12 MPH

Wind Direction - 1 O'clock (30°) Sine .5

To find the 1 MPH wind value, follow these steps: Start by choosing a wind speed to use in your formula; I prefer a 10 mph value for simplicity, but you can use your actual measured wind speed. We'll use this in our wind calculation formula, shown below.

Wind Speed / Gun Number x 1/1000 Distance x Sine = Correction for Wind in Mils

EX: 10 / 4 x .5 x .5 = .62 Mils

To express the formula more clearly: (Wind Speed ÷ Gun Number) × (Distance in yards ÷ 1000) × Sine of Wind Angle. Here, 'Wind Speed' is measured in miles per hour, 'Gun Number' is a ballistic constant specific to your rifle and ammunition, 'Distance' is the range to the target in yards, and the 'Sine of Wind Angle' accounts for the angle at which the wind is blowing relative to the line of fire.

To calculate the 1 mph wind value, use the formula above for a 10 mph wind. Next, move the decimal point one place to the left. For example, a .62 Mils result for 10 mph becomes .062 Mils per 1 mph. Multiply this value for higher wind speeds. Round as needed for practicality and record the process in your d.o.p.e. book for quick reference.

The Sine of our wind angle is based on using the clock method. Every 30 minutes from 12 o'clock (our Target) is an additional 15º. This means 12:30 = 15º, 1:00 = 30º, and so on. The sines of these angles are the percentages of wind we will calculate.

12:30 - 15º = .25

01:00 - 30º = .50

01:30 - 45º = .70

02:00 - 60º = .86

02:30 - 75º = .96

03:00 - 90º = 1

TARGET SIZE IN WIND

Understanding target size in wind is crucial because it tells you how much wind error you have before missing the shot. This value helps you quickly assess risk, make better decisions in the field, and sharpen your wind-reading skills.

If our target is 1 Mil wide and the wind affects our bullet .2 Mils, with everything else being on point, that's a guaranteed hit as far as wind goes. If the target is .5 Mils wide and our wind effect from our min and max is 1 Mil, we have about a 50% greater chance of a miss. The key takeaways are: 1) Knowing the target wind size helps us estimate the probability of a hit. 2) In hunting, it guides our decision on whether to move closer if the shot is risky. 3) Tracking first-round hits when the hit probability is low shows improvement in wind reading. The formula is as follows.

Target size (Mils) / 1 MPH Wind Value = Target Size In Wind

With a 6-inch target at 600 yards (1 MOA), using the information above, our 1 mph wind value is .062, and the target is .28 Mils wide.

.28 / .062 = 4.5 MPH

This means we have to read the wind within 4.5 mph. Remember, it takes 4.5 mph of wind to push our bullet the full width of the target or .28 Mils. If we are aiming center, that cuts the 4.5 mph in half to just 2 mph (2.25 actual), that's a 2 mph wind error on both the high and low sides. If we hold center and estimate a 12 mph wind, and it's actually 9mph on our low side or 15 mph on our high side, then we will most certainly miss. The good news is that with this formula, whether we hit or miss, we can learn what the wind is doing and fine-tune ourselves to what a 9- or 15-mph wind feels and looks like. If we miss to the left, we know we have wind over 14 mph. If we miss right, we know we have less than a 10 Mph wind. We can then use our reticle to see our impact and calculate what the wind was doing at the moment we pulled the trigger.

I only recommend studying our impacts when in what I'll call "learning mode," so as not to create a bad habit of staring through the scope at our impact on an empty chamber. Outside of "learning mode," why we missed doesn't matter. Rechamber, correct your hold, and fire again. Don't sit on an empty chamber. Stay ready to shoot. Once your skill set improves, you will be able to chamber your next round and still spot your impact, creating faster follow-up shots.

Drills to Improve Speed and Accuracy

To help build these skills efficiently, I recommend a specific drill: The Wind Call Challenge. Set up multiple targets at varying distances on a range day dedicated to practicing wind-reading skills. Use your skill set and other indicators to observe real-time wind conditions. With each shot, make a conscious prediction about the wind's effect before firing, then immediately assess the impact relative to your prediction. Repeat this process at different wind speeds to enhance your knowledge and accuracy.

Another effective routine is the Follow-Up Shot Drill. After taking your initial shot, quickly rechamber your next round while keeping your eye on the target. Aim to fire your follow-up shot within a few seconds. This practice not only enhances your speed but also conditions you to make adjustments based on the outcome of the first shot. By using these drills in your regular shooting practice, you'll quickly increase your proficiency in wind calling and follow-up shooting.

Application in the Field

Let's apply the formulas above in a real-world hunting application. We are going to the hill country to hunt a beautiful deer. To increase our chances of success with a fast, accurate shot, we are going to build a few dope charts with our 1 mph wind value and Target size in wind from 300 to 700 yards. This allows us to focus on shooting rather than doing math in the field.

We'll use the same parameters from above, but with a 5-12 mph wind. Because we are using a 4 mph gun at 400 yards, every 1 mph equates to .1 Mils, and a 4 mph wind every 100 yards is 1/100 of the distance In Mils. Let's go ahead and run the math at 400 yards.

5 MPH / 4 (gun number) x .4 (1/1000 distance) = .5 Mils

12 MPH / 4 x .4 = 1.2 Mils

Distance                1 MPH    4 MPH    10 MPH

(Yards)

300                           .075          .3            .75

400                           .1              .4           1.0

500                           .12            .5           1.25

600                           .15            .6           1.5

700                           .18            .7            1.8

Key takeaway: Adjust wind holds by multiplying the 1 mph value by wind speed for fast calculations; half the wind requires half the adjustment, and double the wind needs double the adjustment.

Distance                 6 MPH    8 MPH    12MPH

(Yards)

300                             .45           .6             .9

400                             .6             .8             1.2

500                             .75          1.0            1.5

600                             .9            1.2            1.8

700                            1.05         1.4            2.1

The next step is applying our Sine to our wind value. This can be done by applying the Sine to the wind speed or to our full value hold in Mils.

If we apply the Sine to our full value hold at 500 yards with an 8 MPH full-value wind, we would have a correction of 1 Mil. With the wind coming from 01:00 o'clock, our Sine is .5 or 50%, turning our 1 Mil hold to .5 Mil hold. We can also apply this to our wind speed. 50% of our 8 mph full value wind would be 4 mph. We can run the formula with 4 mph or refer to our chart. 500 yards with a 4mph wind gives a wind hold of .5 Mils. For field expedience, building a chart for quick reference is the best option. You definitely don't want to be doing calculations while the animal you are hunting is within range.

The final step is to find our target size in wind. We can estimate that a deer's vitals are roughly the size of a 10-inch circle. Because we can't accurately Mil a visualized 10-inch circle at 700 yards, we have to use a formula to figure out how many Mils a 10-inch circle would be at 700 yards.

Target size (inches) x 27.77 / Distance ( yards) = Target Size In Mils

10 x 27.77 / 700 = .396 (.4 Mils Rounded)

We can now apply our formula for the target size in wind.

Target size in mils / 1 mph wind value

700 Yards

12 mph wind from 01:00

.4 / .09 = 4.4 mph

If the difference between our minimum and maximum wind speeds is less than 4.5 mph, we have a high probability of hitting our target.

The Overwatch