Long range wind

Discussion in 'Long Range Hunting & Shooting' started by Coyoter, Feb 28, 2006.

  1. Coyoter

    Coyoter Well-Known Member

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    Living in "Windy Wyoming", doping the wind is obviously a concern with any shot over about 100 yards... even with a belted magnum! Of course I have the "toys" to determine distance and wind speed, but is there some advanced (or simplistic) gizmo on the market to precisly determine wind direction? I realize that wind where I'm shooting from vs. where I'm shooting to will be different, but close helps when you can't judge the wind by the waving of the sage brush.
    Many thanks for all help and input.
     
  2. sscoyote

    sscoyote Well-Known Member

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    I use a Speedtech.com watch when i go afield. It has been partly responsible for a couple successful long-range shots just this year on coyotes. As far as the wind direction goes, i just approximate that at full value, 1/2 value, or 1/4 value.
     

  3. Coyoter

    Coyoter Well-Known Member

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    What I've been looking at is the ballistics program readouts for an 800y shot with a 15 mph cross wind. 180gr Scirocco @ 3200 fps. Full value is (according to the program) 43.3" of drift, half value is 30.6" and quarter value is 16.2". Either my program's all wet, or it's not an exact ratio of wind angle to shot angle to figure drift. I'm contemplating trying to make a weathervane with 5 degree increments, but I'd far rather just throw some money at a gizmo if I can.
    Thanks for the input though.
     
  4. remingtonman_25_06

    remingtonman_25_06 Well-Known Member

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    I cant remember exactly how this one guy was doing it, but he was doing it by pointing the way to the target, then drawing the way the wind was going, then multiplying by some number to get the direction. Its something like that. It kinda reminds me of maybe a triangular trick, draw a line to the target, then draw a line the way the winds blowing and you'll get some kinda angle, then you multiply or divide by a certain number or degree, damn I cant really remember. I remember the guy from shooters.com, his name was LRnut. I dont remember the whole process, but he said it worked for him. If anybody else kinda knows what I'm talking about, I'd be interested in it as well. I was shooting at 1150 yards today with a 10-15 mph wind with a 180g btip at 3300fps. For the first 600 yards or so, the wind was going to the left pretty good, but after that, the terrain was different and it was more of a tailwind.
     
  5. Bart B

    Bart B Well-Known Member

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    Long range highpower rifle competitors have been using a simple formula for about 90 years at ranges from 600 to 1000 yards. It goes like this: range (in hundreds of yards) times wind speed (in mph) divided by 10 equals minutes of angle correction for a full value wind.

    A full value of wind is one from either 3- or 9-o'clock relative to the line of fire. Half-value winds were from 1, 2, 4, 5, 7, 8, 10 and 11-o'clock. And a no-value wind was from "supper time" (6-o'clock) or midnight (12-o'clock). This method worked pretty good firing the old M2 173-grain boattail machine gun bullet from .30-06 Springfield M1903 and M1 Garand rifles. It at least got one on the 6-foot square target paper when winds were pretty strong.

    With more recent cartridges shooting bullets that buck the wind a lot better, I've came up with a bit more realistic formula using the same type of simple math. And winds from 1, 5, 7 and 11 are really true half value ones (the sine of 30 degrees is 0.5). Winds from 2, 4, 8 and 10 are really closer to 90% ones (the sine of 60 degrees is 0.87).

    1. Use a very good software program for ballistics such as that sold by Sierra Bullets to calcuate the wind drift for your bullets for each hundred yards of range you'll shoot at.

    2. For each hundred yards of range, convert the bullet's drift in inches for a 9-o'clock 10 mph wind to minutes of angle (MOA).

    3. Multiply each hundred yards of range times 10, then divide that number by the drift in MOA number for that range. The answer is your "magic number" for wind corrections at that range. Note the longer ranges will have smaller magic numbers than shorter ranges.

    In use, you'll need something to measure wind speed. There's many types available from the simple Dwyer Gage to fancy, expensive digital electronic windmills. Then laser or estimate the range. Multiply the range in hundreds by the wind speed in mph then divide that answer by your magic number for that range.

    Example: range is 600, six times indicated wind speed of 4 mph is 24 and dividing 24 by your magic number of 16 (Sierra 30 cal. 180-gr. SBT @ 3000 fps at 3000 ft elevation) equals a 1.5 MOA correction for a full-value 4 mph wind. If the wind's from 4-o'clock, 90% of 1.5 MOA is about 1.25 MOA, so make a 5 quarter-minute click correction to the right, aim, hold very still then take your shot.

    I've used magic numbers for .264 Win. Mag, .308 Win., .30-.338 Win. Mag with much success. It's nice to read my old Dwyer wind gage, do the mental math for a .308 Win. shooting 155-gr. bullets out at 3050 fps at 6000 ft. elevation in a 20 mph crosswind then make the correction on a receiver sight that has 1/5th moa clicks fire the first shot at the 1000 yard target and miss the letter "X" in the center of the 10-inch diameter scoring ring by about half an inch. But then there's been times when I missed it by a couple of feet 'cause the downrange cross winds weren't the same speed as the wind at the firing point.
     
  6. royinidaho

    royinidaho Writers Guild

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    Bart,

    Was shooting today and was serious enough that I put up a wind flag well more of a wind indicator than a flag. Thend during the course of shooting and making the 200yd trip to the target holder I got to thinking, which is usually a bad thing, for me...

    I was wondering if wind from 90 degrees = 100% then is wind from 45 degrees = 50% effective for the same wind speed.

    If I read your post correctly the impact wind with respect to angle varies as the cosine of the angle. Am I understanding correctly??

    I also googled on Dwyer Gage. Hey those things are plenty spendy!! Already have GPS for elevation so I think I'll just add one of those windmill thingers for wind speed.

    However, you lost me completly on the "magic number" /ubbthreads/images/graemlins/blush.gif

    I'll follow your example and do a little figuring and see if I can sort it all out.

    Appreciate the post, thanks...
     
  7. sscoyote

    sscoyote Well-Known Member

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    Roy-- take a look at the Windtronic anemometer-- i picked mine up fairly cheap-- google them, or maybe just google anemometers period. Might find something even cheaper.
     
  8. Bart B

    Bart B Well-Known Member

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    Idaho Roy, first the easy part. The Dwyer Wind Meter I mentioned can be seen at

    http://www.stumpfballoons.com/wind.htm

    and

    http://store.yahoo.com/cspoutdoors/dwyerwindmeter.html

    selling for $22 and $15. Just hold their back side into the wind and read the speed next to the floating foam ball. Hold your fore finger over the top for high winds. Such a deal.

    "Magic numbers" are the number you use at each range for each load (bullet at some muzzle velocity). Each one has to be calculated then memorized or written on a label taped to the back of the wind meter (that's how I used them). Multiply range in hundreds by wind speed in mph, then divide that answer by the range's magic number.

    Example: You've calculated magic numbers for a given bullet as follows:

    200 yards = 18
    300 yards = 17
    and when you get out to the longest range you'll use...
    1100 yards = 11
    1200 yards = 10

    "Magic numbers" can be also called a "wind constant" for a given bullet at a given muzzle velocity at a given range. As range increases, the wind constant gets smaller as wind drift increases in moa.

    Let's say the wind's 14 mph from 2 o'clock and your $5 laser rangefinder says the coyote's 850 yards away. Multiplying 8.5 times the 14 mph wind speed is about 120; dividing 120 by your load's 900 yard magic number of 13 you get 9.2. A 2 o'clock wind is worth 90 percent and 90% of 9.2 is about 8.3. So move your sight 8.3 moa into the wind and nail that prairie puppy pouncer pronto!!!

    The wind's value from some angle is based on the sine of the angle. At 1 o'clock, the sine of 30 degrees is .5, at 1:30 or a 45 degree wind, the sine is .7, at 2 o'clock, the sine of 60 degrees is about .9 and at 3 o'clock the sine of 90 degrees is 1; a 3 o'clock wind is a full value wind. Same numbers apply from other clock numbers that have the same relative angle.

    Hope this helps.
     
  9. Bart B

    Bart B Well-Known Member

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    Roy, here’s another way to get those “magic numbers” or range constants.

    Let’s take a 30 caliber 180-gr. spitzer boattail leaving at 2960 fps at an altitude of 6000 feet. At each range below, the wind drift in inches is for a 10 mph cross wind from 3 o’clock.

    At 400 yards, 8.3 inches, 2.1 MOA correction needed

    At 800 yards, 36.9 inches, 4.6 MOA correction needed

    At 1200 yards, 94.1 inches, 7.8 MOA correction needed

    What’s needed is some number to divide the base formula’s answer (Range in hundreds by Wind in mph) by to get the correction for a full value wind.

    At 400 yards, 4 x 10 = 40, so 40 / 2.1 MOA = 19, the magic number (or constant) for this load at 400 yards.

    At 800 yards, 8 x 10 = 80, so 80 / 4.6 MOA = 17, the magic number (or constant) for this load at 800 yards.

    At 1200 yards, 12 x 10 = 120, so 120 / 7.8 MOA = 15, the magic number (or constant) for this load at 1200 yards.

    Run the wind calculation formula for each range and see what MOA value you come up with for each one. Again, the formula is Range (in hundreds of yards) times Wind (in mph) divided by the Magic number. Or: RxW/M
     
  10. royinidaho

    royinidaho Writers Guild

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    Hmmm, I'll give it a go.

    Was blown off the test range this morning. 90 degree wind was blowing the .243 100gr bullet 5 to 8 inches at 200 yds.

    Only slightly less wind at about 10 degree off of line of sight had minimal effect this afternoon. Was quite supprised. This is the first time I have shot anything smaller than 338 in over a year.......
     
  11. Bart B

    Bart B Well-Known Member

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    [ QUOTE ]
    Was blown off the test range this morning. 90 degree wind was blowing the .243 100gr bullet 5 to 8 inches at 200 yds.

    [/ QUOTE ]
    That's not much wind. Here's a "windy" bit of reality.

    When the US Palma Team started to shoot in the 1988 World Championships Team Match held in Sydney, Australia, the wind was coming from about 8-o'clock. Coming very, very hard. I laid down on the first relay of four on our 16-person team and my coach was talking with the other three behind their shooters. They were deciding how much wind to use on the 800-yard line. It was a toss-up between 27 or 29 minutes left correction for the arsenal 147-gr. bullets we were using in our .308 Win. rifles. 'Twas decided to go with 28. That's 112 clicks on my quarter-minute rear sight. He told me to load and be ready, so I did. Then put on 112 clicks left. "Shoot" he says so I did and called the shot a bit left and high as the wind was buffeting me around somewhat. Target went down then came up with the spotter a bit left and high of center. Such is life when you've got a good wind doper for a coach. My job was to shoot small groups. His job was to keep it in the middle.
     
  12. Coyoter

    Coyoter Well-Known Member

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    Well, I went out today for a little plinking with the .243AI... The breeze was a pleasant 20+ mph out of the west with gusts to 33 according to the Skywatch Meteos. Fortunately the balmy 57 degree temperature made it almost tolerable. About the only thing I really learned today is that at 20+ mph, I blow around way more than the bullet does! Anyone know where I can get a deal on a "portable" concrete bench and wind block?!
     
  13. älg

    älg Well-Known Member

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    Guys, it would be interesting to know what signs from vegetation, etc.. you look at for calculating the speed of wind ..... you can´t always have a wind meter with you.
     
  14. Bart B

    Bart B Well-Known Member

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    The best long range competitive rifle shooters use their spotting scope focused to see the mirage (heat waves) wrinkling across the field of view. By focusing the scope about 2/3rds the target distance, the wrinkles moving across are an exact image of what the wind is doing.

    There are zillions of videos and printed words on the market that try to teach folks how to "read the wind." None of them work well.

    The best way to learn how to do this is to have a very good shot ready to shoot at a 600 to 1000 yard target on a rifle range, then you look through your spotting scope, read the mirage then estimate how much windage correction is needed. You get excellent feedback when the target's spotted on both on how well you estimated the correction as well as how well the shooter performed. As the cross wind speed changes you'll get to change the amount of correction.