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Which Wind to use?

 
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  #8  
Old 08-10-2009, 01:03 PM
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Re: Which Wind to use?

Now you're getting it. The angle created by a wind in the first part of flight stays in effect all the way to the target. I'm making up a drawing of the effect and will get it up as soon as it's done.
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Old 08-10-2009, 01:09 PM
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Re: Which Wind to use?

In the picture below the angle of the flight of the bullet offline to the right is the same is all examples. You can see how the flight of the bullet is effected if the wind is in the first part of the flight and how it effected if the wind is only farther on out.

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Old 08-10-2009, 02:09 PM
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Re: Which Wind to use?

Thanks. ill be waiting....
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Old 08-10-2009, 02:28 PM
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Re: Which Wind to use?

Quote:
Originally Posted by tracker12ga View Post
Alright, I think I just had a eureka moment hear. From what you guys are saying and from another archived post that I read, if you have a wind that pushes the bullet 1" at 100yds, then you will have a 10" drift at 1000yds. Compared to having the wind push at closer ranges to the target, the drift will be less.
but it takes more wind at the muzzle to affect the flight of the bullet.
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Old 08-11-2009, 02:25 PM
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Re: Which Wind to use?

Just keep in mind that the only thing you know for sure IS the wind at the muzzle. The rest is a good guess at best. I personally will try to work out some kind of average based on what I see throughout the whole range I'm shooting.

I think any of us that shoot in canyon country can admit that there's been more times than a few that you make the best guess you can come up with and let one rip.......then go WOW, WTF happened there?

So what does one do?........shoot in the worst conditions you can as much as you can. The more you shoot in crappy conditions, the better your guesses will get.
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  #13  
Old 08-11-2009, 07:35 PM
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Re: Which Wind to use?

What ss7mm posted is an excellent text book explanation. In a perfect world, the 'near' wind usually tends to have more effect than the wind right at the target.

Unfortunately we, or at least *I*, don't live in a perfect world.

The terrain over which you're shooting has a lot to do with what matters - is there a cut in the trees further downrange, allowing a nice 'river' of wind to come through and smack your bullet about? Are there multiple ridges between you and the target that may give you some fits with vertical on target? Etc. and so on.

The 'near' wind theory makes logical sense... if you take the time to work out the numbers for a regular trajectory out to say 1k yds and then use start playing with wind values at various distances, the near wind does have the most effect, despite the velocity decay further downrange. The fly in the ointment per se, is one that most of us don't normally think about all that much - how high the bullet is off the ground at any given point in the trajectory.

Most of us have probably noticed that the wind often seems a lot stronger when we are standing straight up with our head 6'+ into the wind, vs. when we are laying down about a foot above ground. Now consider that your bullet is flying 10-12' over the line of sight, and god only knows how much over the terrain (depending on where you're shooting - even KD ranges aren't perfectly flat)... and the wind speed can pick up considerably as the bullet gets higher above ground. Even then it is rarely consistent.

So in effect its probably not so much the 'near' wind, nor the 'far' wind, but more the 'mid' wind where the bullet is at the apogee of its trajectory.

To be fair, this isn't something I came up with on my own. It's something I read in Bryan Litz's new book 'Applied Ballistics', and kind of smacked myself in the head as I read it, as it explains (to me) why when I get a firing point where I can actually use my spotting scope to watch the mirage, most long-range KD shooters focus back to about 2/3 the distance down range - which is awful close to the 'peak' of the trajectory.


YMMV,

Monte
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  #14  
Old 08-11-2009, 07:58 PM
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Re: Which Wind to use?

You need to TRY to take into account how any/all winds can affect your bullet. SS7MM is correct in saying the earlier in a bullets flight the wind deflects it from its original path the greater the deflection will be at the intended target. Milanuk is correct in saying that the wind velocity is usually higher at the bullets maximum ordanance (highest point in trajectory) which is approximately 2/3 the distance to the target (according to ballisticians that work for the military).
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