Wind Advice - can you help?

Discussion in 'Long Range Hunting & Shooting' started by Subsonic Flyer, Aug 21, 2006.

  1. Subsonic Flyer

    Subsonic Flyer Member

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    I use a wind meter and charts to help me adjust for normal wind conditions but yesterday I was faced with a situation that I was unsure of how to deal with. I was preparing for a 400 yard shot with a 10 mph wind from 9.00 o'clock (full value) but after 200 yards a large wood acted as a screen and judging by the leaves and grass there was no wind for the remaining distance to the target.

    Should I have calculated the wind for only the first 200 yards or is there a formula for this type of situation? Any advice would be greatly appreciated.

    My setup is a 26" heavy barrel Steyr .308 155g Amax which would have given 12.6" of drift under normal conditions.
    SF
     
  2. overbore

    overbore Well-Known Member

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    As a positive suggestion, divide the total distance into thirds. Use the near wind to get the basic "hold into- click into" direction then use the last third as the most important as that is where your round will spend the most time. Suggest you print out ( as in Load From a Disk ) the wind defelction chart and you will see the deflection for yourself. Get first 1/3rd and last 1/3rd aligned as to same conditions and record your shot after careful trigger release. Overbore /ubbthreads/images/graemlins/cool.gif
     

  3. Subsonic Flyer

    Subsonic Flyer Member

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    OverBore
    Thanks for your reply.
    I am still a little confused. I have several ballistics programs that will estimate the wind at varying angles and speed but what I am unsure of is how do you adjust for varying conditions along the bullet path for a given shot? If half the distance to the target has 10 mph wind and the second half has only 3 mph how would you calculate this prior to taking the shot?
     
  4. overbore

    overbore Well-Known Member

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    SubSonic: ( I spent most of my professional years flying at Mach .78) visualize a plot of your bullet trajectory; the rate of curve increases with the distance, right. Now mentally rotate that curve 90 degrees so that the curve's greatest distance is off to the right. You are now looking at a 1,000yard wind diagram with a 9 o'clock wind from the left. The greater the distance the greater the wind effect. Even with a Horus system, you must fire one shot and see if your calculations and adjustments are valid. KD shooting allows the use of spotting discs but field uses require that you follow through to see your bullet's impact then correct with your second shot. NO systm I know of can do better. Overbore /ubbthreads/images/graemlins/frown.gif
     
  5. overbore

    overbore Well-Known Member

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    Two updates for you Sub Soncic ( actually three ) First, change Mach no. to .82, next From www.creedmoresports.com order C1255 @ 9.95 "Reading the Wind and Coaching Techniques" and the last is "When the Wind Blows." Best wishes, Overbore
     
  6. eshell

    eshell Well-Known Member

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    [ QUOTE ]
    I use a wind meter and charts to help me adjust for normal wind conditions but yesterday I was faced with a situation that I was unsure of how to deal with. I was preparing for a 400 yard shot with a 10 mph wind from 9.00 o'clock (full value) but after 200 yards a large wood acted as a screen and judging by the leaves and grass there was no wind for the remaining distance to the target.

    Should I have calculated the wind for only the first 200 yards or is there a formula for this type of situation? Any advice would be greatly appreciated.

    My setup is a 26" heavy barrel Steyr .308 155g Amax which would have given 12.6" of drift under normal conditions.
    SF

    [/ QUOTE ]

    IMHO, I would hold/dial for a half-value wind, i.e.: use data for a 5 mph 9 o'clock breeze.

    I say this because the wind only seems to have effect over one half the course.

    There is a lot of controversy about which part of the wind is most important, whether the greater angular dispersion at the muzzle will affect bullet flight more than wind at the target, which is now working on a slower moving bullet. . . no one of authority can seem to agree. In either case, you will only see the effect of half of the wind influence and a half value wind would get you 6.3" hold-off. Even accounting for a very minor difference in wind effect over "which half of the course?", you'll still end up with an extremely close first round impact.
    /ubbthreads/images/graemlins/cool.gif
     
  7. Subsonic Flyer

    Subsonic Flyer Member

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    Thank's for your replys E.Shell and Overbore both very usefull. I will certainly be ordering some reading material to further my knowledge in this area.
    SF
     
  8. Bart B

    Bart B Well-Known Member

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    [ QUOTE ]
    There is a lot of controversy about which part of the wind is most important, whether the greater angular dispersion at the muzzle will affect bullet flight more than wind at the target, which is now working on a slower moving bullet. . . no one of authority can seem to agree.

    [/ QUOTE ]The wind closest to the shooter is the most important. All the coaches on long range rifle teams around the world know that. Other top competitors at long range know that, too. Some long range hunters know this: see below:

    http://longrangehunting.com/ubbthreads/s...part=1&vc=1

    It's easy to see what wind has the most effect by using ballistic software showing wind drift, plotting the wind drift curve as a graph, then laying a straight edge tangent to any point on that drift curve. It's then easy to see there's about three times as much wind drift distance caused by a given wind across only the first third of the bullet's flight as there is for only the last third.
     
  9. overbore

    overbore Well-Known Member

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    Different opions allowed? Coaches at highpower may "know" that concept but winners ( note I did not say shooters) at 1,000 yd br have the opinions I posted prior to yours.
    What ever works is key which is why I use Horus on the important rifles as the combo of large Vias brake and the ability to locate the "miss" for the second shot hit is a given. Overbore ps do a search on Benchrest central forums-- this is where the LR accuracy folks post.
     
  10. Bart B

    Bart B Well-Known Member

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    [ QUOTE ]
    Different opions allowed? Coaches at highpower may "know" that concept but winners ( note I did not say shooters) at 1,000 yd br have the opinions I posted prior to yours.

    [/ QUOTE ]Opinion's are plentiful and I respect yours. And long range highpower competition rifles are just as accurate as benchrest rifles but few folks know this. There's winners in every shooting discipline including highpower competition. But only one fact about wind over long ranges.

    Of course bullets drift from wind more at lower velocities than higher ones. But folks usually forget (or don't realize) that the direction a bullet's traveling after the first third of the range where wind is makes it strike further from the aiming point than if the same wind speed was only in the last third.