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Thread: Wind chart

  1. #16
    Protea Benchrest (Air) Team '13

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    Thing is, the horizontal part works more or less the same for rimfire and pellet, but in my limited experience, the vertical deflection works just the opposite. Wind from 3o'clock, deflection will be lower and from 9o'clock it will deflect higher. Like I said, personal experience from all my guns with right hand twist barrels and confirmed by Gert v Wyk. When I started this diagram confused the hell out me until I figured out that it does not apply to airguns. Can anyone else confirm this, or have I lost it?
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  2. #17
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    Quote Originally Posted by EugeneDP View Post
    Thing is, the horizontal part works more or less the same for rimfire and pellet, but in my limited experience, the vertical deflection works just the opposite. Wind from 3o'clock, deflection will be lower and from 9o'clock it will deflect higher. Like I said, personal experience from all my guns with right hand twist barrels and confirmed by Gert v Wyk. When I started this diagram confused the hell out me until I figured out that it does not apply to airguns. Can anyone else confirm this, or have I lost it?
    I can confirm that I agree with you!

    for a more useful insight to the diagrams at the beginning of this post:

    Imagine you are dividing up your FT course into segments. starting at 25y to 30y, 30y to 40y, 40y to 50y, 50 to 55 yards.

    the wind drift of a 12 ft/lbs pellet will be very close to the following pattern irrespective of strength, because wind displacement is a constant force unlike gravity which is an accelerating force (speeds up the more it drops).

    25-30y = 1x
    30-40y = 2x
    40-50y = 3x
    50-55y = 5x

    "x" is equal to the amount that the pellet is moved by the wind. So if yourpellet is moved by 1/2 an inch at 25 yards it will move by 2 1/2 inches between 50-55 yards (5x 1/2 inch)

    It also works in reverse, so if you notice your pellet has ben shifted 5 inches horizontally between 50 -55 y, then it will be shifted by 1 inch at 25-30 yards. Its an approximation, but quite close. I could post the entire printout of the data I used, but its useless to do that, as the pattern is all that is important.

    Using the above pattern to assess what is happening in the wind at any given time (providing the wind is the same from shot to shot) can allow you to judge short shots to long shots in a lane and use the feedback to adapt when the wind is causing you grief. Of course you have to watch for the switches!

    I also use a table I printed out, which tells me all the distances and how much my pellet will move in any mph.......but its complicated so I just memorized one set of numbers for 10mph at all distances and that allows me to be adaptable and make decisions on the fly.

    I don't consider that I am beating the wind, rather "negotiating" a better solution than not knowing or doing anything.

    The problem I have sen in many forums is that when shooters say "experience" is the only way to get good in the wind, they actually mean "I'm not sharing what I know".

    It is common sense, and applying things that you understand like what an inch looks like on an FT target faceplate, so you can make a judgement call about how much the pellet has ben blown off your point of aim.

    One more thing I noted was that if you try and use a ballistic program to get your wind displacements, it will be innaccurate if you use the same BC for both trajectory/drop, and windage. Because gravity accelerates the vertical displacement, but wind does not, the BC used must be different to get accurate figures out of the software. Usual story.....

    GS
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  3. #18
    Sharp Shooter
    SAFTAA FT Colours '19

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    Quote Originally Posted by greyskullnz View Post
    I can confirm that I agree with you!

    for a more useful insight to the diagrams at the beginning of this post:

    Imagine you are dividing up your FT course into segments. starting at 25y to 30y, 30y to 40y, 40y to 50y, 50 to 55 yards.

    the wind drift of a 12 ft/lbs pellet will be very close to the following pattern irrespective of strength, because wind displacement is a constant force unlike gravity which is an accelerating force (speeds up the more it drops).

    25-30y = 1x
    30-40y = 2x
    40-50y = 3x
    50-55y = 5x

    "x" is equal to the amount that the pellet is moved by the wind. So if yourpellet is moved by 1/2 an inch at 25 yards it will move by 2 1/2 inches between 50-55 yards (5x 1/2 inch)

    It also works in reverse, so if you notice your pellet has ben shifted 5 inches horizontally between 50 -55 y, then it will be shifted by 1 inch at 25-30 yards. Its an approximation, but quite close. I could post the entire printout of the data I used, but its useless to do that, as the pattern is all that is important.

    Using the above pattern to assess what is happening in the wind at any given time (providing the wind is the same from shot to shot) can allow you to judge short shots to long shots in a lane and use the feedback to adapt when the wind is causing you grief. Of course you have to watch for the switches!

    I also use a table I printed out, which tells me all the distances and how much my pellet will move in any mph.......but its complicated so I just memorized one set of numbers for 10mph at all distances and that allows me to be adaptable and make decisions on the fly.

    I don't consider that I am beating the wind, rather "negotiating" a better solution than not knowing or doing anything.

    The problem I have sen in many forums is that when shooters say "experience" is the only way to get good in the wind, they actually mean "I'm not sharing what I know".

    It is common sense, and applying things that you understand like what an inch looks like on an FT target faceplate, so you can make a judgement call about how much the pellet has ben blown off your point of aim.

    One more thing I noted was that if you try and use a ballistic program to get your wind displacements, it will be innaccurate if you use the same BC for both trajectory/drop, and windage. Because gravity accelerates the vertical displacement, but wind does not, the BC used must be different to get accurate figures out of the software. Usual story.....

    GS
    Hi GS, this is probably the first post that I've been able to understand and make sense of with regards to making adjustments for wind. Thanks for the info.....the newby appreciates it!
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  4. #19
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    My pleasure.

    The wind chart at the top of the thread is true for large calibre bullets.

    For .22 cal smallbore bullets it follows more of an oval than an "S".

    For .177 cal pellets it is in fact in reverse, and almost completely flat up to about 10mph wind, which at 12 ft/lbs means there's virtually no vertical displacement until the pellet has been shifted more than 3 inches horizontally. I have no hard data on exactly how much, but have a gut feeling the ratio is about 1:10, meaning one inch vertical displacement for 10 inches horizontal displacement at 20 mph approx.

    And it is in reverse direction for a diabolo pellet to a bullet shape. Has to do with where on the projectile the Centre of Pressure is effecting, and where the Centre of Gravity is located, and the magnus moment effect.

    So just imagine a long almost flat oval, that leans down slightly to the left (R to L wind) and up slightly to the right (L to R wind).

    cheers
    GS
    Last edited by greyskullnz; 12-10-12 at 19:26.
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