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Calculating drop with head or tail wind?

 
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  #1  
Old 09-21-2009, 03:34 PM
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Calculating drop with head or tail wind?

Hey all,

Anyone have a formula for calculating drop with head or tail wind? Or just some good insight.

Thanks,

Steve
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Old 09-21-2009, 05:24 PM
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Re: Calculating drop with head or tail wind?

I think there is a good reason this isn't discussed, because it will have very little effect on the flight of a high BC bullet. But hey, that's just my hunch.
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Old 09-21-2009, 08:05 PM
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Re: Calculating drop with head or tail wind?

Just ran a test with Exbal. Used generic 308 ballistics (175grain SMK BC = 505, 2600fps). With 10mph wind from 12 o'clock and 6 o'clock. This changed the scope adjustment by .5moa at 1k.
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Old 09-21-2009, 10:35 PM
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Re: Calculating drop with head or tail wind?

Where a head or tail wind does have an effect is when it is up or down slope (especially a steep slope).......Rich
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Old 09-21-2009, 10:37 PM
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Re: Calculating drop with head or tail wind?

The example below is not technically 100% correct but it is so close it is scary.

You can find the FPS of the wind by converting it from MPH. Add or subtract the FPS of the wind (subtract for a head wind, add for a tail wind) from your true FPS and you will be within a small fraction of an inch at 1K with a 10 MPH wind. The conversion number is 1.467

MPH * 1.467 = Feet Per Second.

PS:

Steve, that excell file I sent you corrects for head winds and tail winds.
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Old 09-21-2009, 10:59 PM
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Re: Calculating drop with head or tail wind?

Quote:
Originally Posted by Michael Eichele View Post
The example below is not technically 100% correct but it is so close it is scary.

You can find the FPS of the wind by converting it from MPH. Add or subtract the FPS of the wind (subtract for a head wind, add for a tail wind) from your true FPS and you will be within a small fraction of an inch at 1K with a 10 MPH wind. The conversion number is 1.467

MPH * 1.467 = Feet Per Second.

PS:

Steve, that excell file I sent you corrects for head winds and tail winds.
Thank you Michael,

If a wind is not straight on to the path of the bullet, does it have more surface area to act on than when it is straight on? Such as a two o'clock wind.

The winds that we dealt with yesterday were very turbulent and it may be as suggested earlier that we had a down draft we were dealing with. That and all but one of the rifles that we had on the outing were in one stage or another of development. The one rifle that had a proven load did not perform predictably vertically either.

Seems to me that long range shooting works better when it is calm.

Thanks all for the info.

Steve
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Old 09-22-2009, 12:22 AM
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Re: Calculating drop with head or tail wind?

Mathematically with a wind other than 6 or 12 O'clock a bullet will have a measure of up or down varience as well as a sideways varience. Of course there is always the vertical component of crosswinds but for simplicity sake lets forget about the minor technical issues.

You ask a good question. To the letter of physics, I cannot offer you an honest answer. Mathematically I can help you.

That said, if you had a proven load not acting normal vertical, I would ask if you accounted for ALL of the enviornmental factors such as temp, humidity, pressure. Raw pressure that is and NOT altitude. Also, was the powder hotter or colder than normal? Were you able to accuratey judge the windage at locations other than the firing line and the target?

What was the distance fired? How 'proven' is the load? How well have you documented the velocity of the load (ie: how many sessions have you chronied the load in different temps)??

There is a reason your load did not perform as expected. There is a reason AND an answer. You just have to perform the proccess of elimination tactic to find the answer. Be honest!
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Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.

Last edited by Michael Eichele; 09-22-2009 at 12:26 AM.
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