Wind Ballistics

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CaseyJohnson

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I shoot a 175 grain .308 bullet from a custom HOWA 1500. I have recenntly decided im interested in trying to shoot up to 800-1000 yards. At this rangethe wind and humidity become a factor. What tools or formulas can I use in order to calculate how much to adjust my windage dial?
 
I shoot highpower competition. I have simple thumbrules for our fixed distances. If I get "lost" (usually shoot fast to keep up with the changes; sometimes I forget how much I have on), I'll go to a rosette (shows windage for different wind speeds and direction).

Dialing on the right windage is easy. It's figuring out the wind speed and direction that's hard.
 
There are lots of online programs were you can plug in data to caculte bullet drop and wind drift. I like this one. It is pretty simple to use.

http://www.hornady.com/ballistics-resource/ballistics-calculator

You will have to click on the "advanced" setting in the upper right corner to calculate wind drift.

You really need a chronograpy for any accuracy. If you are just guessing at YOUR guns velocity the numbers here don't mean much. You cannot count on ballistcs charts. I've seen rifles with identical barrel lengths shoot ammo from the same box with over 100 fps difference between the 2.
 
"Accuracy 1st Quick Wind Formula", is easy, fast, and works really well.

For .308 you use .1 mil per 100 meters for each 4 MPH of full value wind out to 600 meters, and add .1 mil beyond.

So at 500 meters, in a 8 mph full value wind, your wind dope is 1 mil (500 = .5 mil, x 2 for 8mph)..

For 800 meters in the same wind, your dope is 1.8 mils, (800 x .1= .8m +1 for range beyond 700m = .9, x 2 for 8mph).

The biggest factor though is experience. Find a range near you shooting LR matches, and go shoot a few.
 
Go to the CMP Bookstore and check out their guides, books and CDs on rifle shooting. Concentrate on the Service Rifle Guide and the SDM DVD. Both will give you an ideal on what you are looking for. Both cost $6.95 each. Granted they deal with Service rifles (ARs,) but the principle is the same.

https://estore.odcmp.com/Store/login/login.aspx

I've shot the M1A in 308 for about 35 years in high power at 1000 yards, using pretty much the same round as you're using. A 175 Grn SMK at 2500 - 2600 fps.

The formula you're looking for is R*V/10

R is the range in 100 yards. V is the wind speed in MPH, 10 is the constant for the round you're using.

Lets say you're shooting in a 8 MPH wind at 1000. It would be 10*8 = 80/10 = 8. So in a full value wind you'd turn your sights 8 MOA into the wind.

To determine wind speed you can use the conditions, blowing grass, tree limbs, trees, etc. or Range flags. Wind meters give you an ideal but only at the firing line or where you're standing, not down range.

If you have range flags, pick the one mid to 2/3s distance down range.

If you look at a flag you'll notice its blowing out from the flag pole. As the flag stands out, it creates an angle. Divide that angle by 4. That would give you an estimate the wind speed.

So lets say again you are shooting at 1000 yards. you see the angle of the flag is 40 degrees. 40/4 = 10. Now using the formula above. 10 * 10 = 100/10 = 10 clicks of windage to correct for the wind.

That is full value wind. If the wind is coming from 7-8 O'Clock, or 2 or 10, etc etc that would be a half value wind so using the above example you'd need 5 Min's of correction.

This is just the basics. As you learn, and get experience you'll learn to use mirage which in my opinion is a more accurate method.

The books and what you read here is just a guide. To learn shooting in the wind takes practice, lots and lots of practice.

As to temp. based on the round your using, every 10-15 degree change in temp will move your impact 1 MOA, an increase means the bullet will go faster so you come down one min. if the temp cools down so does the velocity so you add a click.

Light: Sun up sights up, sun down sights down. Meaning if you're shooting in bright sunlight, and clouds move in, come down one minute.

The same as to the difference in the position of the sun. If you start shooting in the morning and the sun is on your left you have one sight setting. So come after noon the sun is on your right. Click to the right one MOA. Click into the sun.

Like I said this is all basic. Everyone sees things different because our eyes are different. The above informant ion worked for me in the 15 or so years I coached the Alaska National Guard Rifle team and it still works in my Instructing CMP GSM Clinics.
 
I've long held a suspicion that bullets were fired long distances before computers
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LOL, yeah I have books by Hatcher and Edward Lewis written before and after WWI on rifle shooting.

Both give the same information as I just provided, plus its what I was taught in Sniper School and the NGB MTU's Coaches Clinic..........long before I was into computers.

One thing I did forget to mention is score or data books. Keep records of every shot you fire, and the conditions for that shot. Write down EVERYTHING.
 
Most everything we do today was possible before computers. Your cellphone has about 10X the computing power of the Apollo 11 craft that first landed on the moon. Many of the complex math problems solving trajectory to put them on the moon and get them back was done on a slide rule, or by hand on paper.

But they do make things faster and easier.
 
I'll take a computer over a book any day...
If you have a Droid phone, download Strelok... it's free, accurate, and loaded with features.
 
All those calculations and formulae and computer apps work fine after you crank in the wind speed and direction, not just at the firing line, but downrange 800 yards. Even range flags are not accurate (what are the flags made of, how heavy is it, did it get wet in the rain last night, etc.) at the firing line, and few ranges have flags all the way out.

If you can get a range to let you install them there are anemometers with radio transmitters to send the data to a receiver, which you install on your bench....

Or you can just guess. Or you can call it "doping" the wind, which is another name for guessing.

Jim
 
Regardless whether you use a computer or not, you need a data/score book.

Many things don't show up on a computer, like your position change, and what it does to your zero for example. Not many computer programs have light conditions and what light does at differant angles.

If you use a M1907 sling, there is no place in computers that mention the hole spacing for the clips, how are you gonna know when the sling requires changing holes, or maybe even replacing the sling.

I could go on all night with examples but you get the ideal.

I've been using computers off and on since the mid 90s (internet that is). I've lost my data more then once. Just last week I lost all my documents and pictures.

All those calculations and formulae and computer apps work fine after you crank in the wind speed and direction, not just at the firing line, but downrange 800 yards
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Computers wont catch a boil, that takes a shooter. Computers don't read mirage. That takes a shooter.

You record what mirage you see and what it does to your bullet.

I've never seen it done, but it would be fun to watch someone try to use a computer or ipod program during an infantry match. That takes a coach with 10X field glasses reading mirage.

Electronic devices are fun to play with, but I wouldn't trust my life to them.

I have score books going back to the 70s, Still readable.

No one, regardless of whether you use a computer or not should do any serious shooting with using a data book.

Record everything. If a fly goes by and hic-up, write it down. Take the data home and put it on your computer later if you want, but keep your notes.

You'll never know when you'll need them.

Learn to make corrections by what you know of the wind/mirage. If you're hunting and spot a nice elk across the canyon, chances are he's not going to wait around while you imput data. If you've learned wind the old fashion way, you can simple glace at the trees, get a reading and make the shot.

Also I've spent a great deal of time in Alaska (22 years to be exact). It gets nippy up there and many places in the lower 48. Cold whether eats batteries, computers take batteries.

A pencil works in all weather conditions.
 
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Computers are great but they can not read the wind.

The key is to practice, practice and more practice. Doing the math is easy, the wind is the X factor and knowing what the X factor is, that's the difficult part.

Or shoot on calm days only;)
 
Reading the wind is an accumulation of range experience . Electronic devices can offer a lot of secondary information and theoretical solutions but the shooter is the one responsible for observing conditions , evaluating the intangible values of temperature,humidity,mirage,light and wind. Then, with or without ballistic formulas or electronics, figure a response based on those intangibles. Most of this will come from being on the line and actually seeing what the wind does to a bullet. Then accurately recording the results in a data book or tablet for future reference. The best wind readers I ever encountered just seemed to have a special sense. Kraigwy's posts are the short, and well written answer to the big question .
 
DaseyJohnson:

When I was shooting on a Marine Corps rifle team I paid little attention to what I thought the wind velocity was. What I did is rely on my experience with the effects of the range conditions and what effect that they had on my bullet's wind drift. What I did was to walk up to the firing line and put on my rifle's zero. Next, I would look at the effects the wind was having on the grass, tree limbs, somke behind the firing blowing dust and anything else out of the ordinary. Important is to evaluate the conditions not only at the butts but mid range also. After I evaluate the conditions, from memory and my data book, I moved my sights to componsate for the conditiions, I evaluated necessary sight moves for every shot slow fire. it's called keeping in step with the wind.

Semper Fi.

Gunnery Sergeant
Clifford L. Hughes
USMC Retired
 
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