Quick Wind, also known as the B.C. Method or Gun MPH is a way to calculate and dial for the wind. In my opinion, it's the easiest and fastest way to calculate and adjust for the wind. Once you understand how it works, it can be used on almost any gun with any caliber. It doesn't work well with slow-moving bullets such as sub-sonic ammunition or very low B.C. bullets like a 150-grain 300 blackout starting at 1600 fps. For every other bullet, it works very well and works best with high velocity, high B.C. bullets. Unless I’m shooting past the capability of the quick wind method, then it is all I’m using. Outside of using the quick wind method, I use charts and my Kestrel. Let's take a look at how to use this method.
Ballistic Calculator and B.C. Method
To use the Quick Wind method I need some data. With this data, you will also understand the other names of this method. I like to use my ballistic calculator to get the data after it has been trued because I like to see the bullet's path. If you are using a ballistic calculator make sure to turn off spin drift and Coriolis. I like to start by setting the distance at 500 yards. Next, I set the wind to 90º (full value) and then set the wind speed. I start with 4 MPH. What I am looking for is to have a .5 mil hold at 500 yards. I'll increase the wind speed until I'm at a .5 Mil hold or very close. Next, I'll check between 200 and 700 yards. I'm looking to see that at 200 yards I have a .2 Mil hold, 300 yards .3, and so on. Depending on your rifle and bullet this method should work out to about 600 to 800 yards. My .308 is a 4 MPH gun. With a 4 mph full-value wind, from 100 - 800 yards I can use this method. This is where the “Gun MPH” comes from.
The other way is much more simplistic. I'd extract the gun’s MPH from the B.C of my bullet. With my .308 I’m using a 175 SMK. The G1 B.C from Applied Ballistics is .475. I use the first digit of the G1 B.C. In the case of the 175 SMK, it’s 4. With this data, I can call wind on almost any .308 rifle with great accuracy.
Explaining The Math
Let's put the Quick Wind method into practice and see how it works in different conditions. I’ll use the same gun in this example as above, a .308 with 175 SMK, 4 MPH gun. I use the clock method for cosines and DOF is always 12 o’clock.
EX. 1
Wind - 4 mph from 3 o’clock
Distance - 500 yards
We have a full-value wind of 4 mph. Because the wind and gun number matches I know my wind hold will be .5 mils. In this situation, 1/100 of my distance is my hold.
EX. 2
Wind - 6 mph from 3 o’clock
Distance - 500 yards
I look at finding the solution like this, 4 mph gives me .5 mils, 8 mph gives me 1 Mil.
6 mph is halfway between 4 and 8 mph. So, I need halfway between .5 and 1 Mil.
Halfway is .75 mils. It’s that easy.
EX. 3
Wind - 12 mph from 3 o’clock
Distance - 400 yards
When the distance and the gun mph match I call this the sweet spot because every 1 mph equals .1 Mil.
I always start by counting by the gun number.
4,8,12 mph (4x3=12)
In mils - at 400 yards .4 Mils, .8 Mils, and 1.2 Mils
In this situation, my wind hold is 1.2 Mils for a 12 mph wind from 3 o’clock
Time to get more complex. I'll have to adjust for the wind angle. To do so I need to know the cosines of the angles. Luckily, there easy to remember.
12:00 and 6:00 o’clock are 0
12:30 - .25
1:00 - .50
1:30 - .70
2:00 - .86
2:30 - .96
EX. 4
Wind - 12 mph from 1 o’clock
Distance - 400 yards
Count by 4 up to 12 or divide 12 by 4 = 3
3 x 4 (4 because we are at 400 yards) = 1.2 Mils
1.2 Mils is my full-value wind hold. Now I need to adjust for the wind angle. The cosine for 1 o'clock is .50. You can think of this in a few different ways and pick what is easiest for you.
1.2 x .50 = .6 Mils
12/2 = .6 Mils
50% of 12 = .6 Mils
Let's use every cosine with this example.
My full value is 1.2 Mils
The cosine for 12:30 - .25
1.2 x .25 = .3 Mils
12/4 = 3 (4 is because 4s gives you 1/4 which is .25 or 25%)
25% of 12 = 3
1:30 - .70
12 x .70 = .84 (.8 rounded)
70% of 12
30% of 12 = Y (Y - 12)
In this situation, it’s easier for me to get 10% of 1.2 and then multiply by 3 for 30%. Then subtract that 30% from 12. It sounds complicated but for me, it's fast and easy and looks like this. (Keep in mind, my goal with the use of this formula is to not rely on tools such as a calculator.)
To get 10% move the decimal to the left one place.
10% of 1.2 is .12
.12 x 3 = .36 (.36 is 30%)
subtract .36 from 1.2 = .84 Mils (subtracting 30% (.36) from 1.2 = .84 which is 70% of 1.2
I do this the same way with 2:00 and 2:30 except I round 86 to 85 and use 5%
The cosine for 2 o’clock is .86 (85 rounded)
10% of 1.2 = .12
5% is .06
I need to subtract 15%
10% (.12) + 5% (.06) = .18
1.2 - .18 = 1.02 Mils or 85% of the wind value
If this seems too complicated it’s probably only because I am explaining in detail how I do the math. I’m not very good at math, so I break it down into its simplest form. For me, I can have the answer in just 2 or 3 seconds. Doing it this way allows me to do the math in my head without using a calculator or writing out the formula on paper.
EX. 5
Wind - 10 mph from 1:30
Distance - 600 yards
First, I establish my baseline by counting by 4s in mph (my gun number)
4, 8, 12, I am somewhere between 8 and 12 mph
Next, assign a value.
At 600 yards 4 mph = .6, 8 mph = 1.2 and 12 mph = 1.8
These value derive from .6 Mils @ 600 yards per 4 mph
In this situation, 10 mph is halfway between 8 and 12 mph
Halfway between 1.2 and 1.8 is 1.5 Mils
Wind angle - 1.5 x .70
I look at this as subtracting 30%
10% of 1.5 is .15
.15 x 3 = .45
1.5 - .45 = 1.05 Mils
At 600 yards this is another “sweet spot” as I call it. Another way to get my full value wind at 600 yards is to multiply my full wind value by 1.5, or as I look at it, split my full value in half, then add that half to my full value. For every 1 mph, I will adjust .15 Mils. My sweet spots are 200 yards (split full value in half every 1 mph = .05 Mils) 400 yards (every 1 mph = .1 Mil) 600 yards (every 1 mph = .15 Mils) and 800 yards (full value x2, every 1 mph = .2 Mil) this makes getting my full value wind, much quicker and then if I need to, I can adjust for the cosine.
ERROR
This method isn't 100% accurate. However, it is very close with an error at around .05 Mils. If you're using a ballistic calculator you may see that at 300 yards you’ll have an adjustment of .24 Mils. Many ballistic calculators will round this down to .2 Mils. Using the quick wind method I got .3 Mils with an error of .06. My answer for this is that I don’t think most ammo is accurate within .06 Mils or most rifles. If I would like to be more accurate I can use 5 mph as my gun number out to 500 yards. At 600 out to 900 yards I can use 4 mph and this will correct the small error. But, by using 4 mph I get the best accuracy throughout its full range. The error that I do get is at shorter ranges means the error is smaller. .1 Mils at 200 yards is less than .75 inches vs .1 mil at 800 yards having an error of 2.88 inches. It is an error nonetheless that I want you to be aware of.
Expanding Your Knowledge
Another big benefit of the Quick Wind method is giving other people a wind call with a rifle or caliber I don’t normally shoot. After looking at the B.C. of some of the most popular bullets with common caliber I came up with a short list.
.308 - 4 mph
30.06 - 5 mph
6.5 C - 6 mph
300WM - 7 mph
.338LM - 8 mph
With this information, I can easily help someone get on target very quickly. In a hunting situation or worst-case scenario if I end up with a firearm I don’t normally shoot I will be a lot more accurate more quickly knowing and using this data. I’d like to reiterate how simple this method is. Because I’m not good at math I tend to add more steps. These additional steps are for me easier allowing me to do math in my head very quickly. Because I can calculate the wind in my head I'm not relying on equipment that can quit working like a cellphone screen in the summer when it's over 100ºF or when battles die. Paper charts can get wet or blow away in high wind.
You are the weapon and your skill set is what will set you apart.
The Overwatch
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