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Calculating drop with head or tail wind?

 
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  #8  
Old 09-22-2009, 12:47 AM
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Re: Calculating drop with head or tail wind?

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Originally Posted by Michael Eichele View Post
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!
The honest answer is... Not enough accuracy in all the elements to know for sure where the bullet would hit. We use altitude for the pressure, temp was good at 50 to 55 deg. Wind for us at this stage of the game is nothing more than our best guess. I have always saved the long range shooting for calm weather.

Thanks again,

Steve
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  #9  
Old 09-22-2009, 12:56 AM
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Re: Calculating drop with head or tail wind?

What was the distance?
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Originally Posted by Broz View Post
Please just answer one very simple question. Why would anyone shooting long range load a low BC , low SD 168 gr offering in a 300 win???????

My answer to this is. The only reason is to make the 7 RM look good. There is no other reason.

Jeff.
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  #10  
Old 09-22-2009, 01:10 AM
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Re: Calculating drop with head or tail wind?

At 575yrds my calcs worked out well. Moved to 1038yrds and had a tough go. 1 out of three was a good shot. Other two went low in the dirt.

Steve
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  #11  
Old 09-22-2009, 10:03 AM
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Re: Calculating drop with head or tail wind?

Chapter 7 of Robert L. McCoy's "Modern Exterior Ballistics" gives the equations for head and tail winds. It's simply the amount that gravitational drop changes due to the increase or decrease in the time of flight of the bullet to the target,. The effect increases with more than the square of the distance to the target, so it can be significant at long range.

Most commercial ballistics programs are based on McCoy's work and included the calculations. To see the effect just run the programs and look at the effect. Also try it with the wind angle a few degrees offset to see what's important.

Last edited by LouBoyd; 09-22-2009 at 05:03 PM.
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  #12  
Old 09-22-2009, 12:53 PM
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Re: Calculating drop with head or tail wind?

Been thinking about this a little and a 20 MPH wind is eqivilent about 30 fps, which will rsult in about a 2 1/2" difference in drop. I dont think the head wind itself is the cause. It may be the buffeting action of the wind with up and down drafts. But still doesn't seem like it would have a big effect. Maybe it was enough to cause some slight instability and those bullets are right on the stability edge with your 10 twist. This might be a dumb question, but any chance your muzzle was being slightly moved by the wind?

We will probably never figure this out
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  #13  
Old 09-22-2009, 11:43 PM
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Re: Calculating drop with head or tail wind?

Quote:
Originally Posted by MontanaRifleman View Post
Been thinking about this a little and a 20 MPH wind is eqivilent about 30 fps, which will rsult in about a 2 1/2" difference in drop. I dont think the head wind itself is the cause. It may be the buffeting action of the wind with up and down drafts. But still doesn't seem like it would have a big effect. Maybe it was enough to cause some slight instability and those bullets are right on the stability edge with your 10 twist. This might be a dumb question, but any chance your muzzle was being slightly moved by the wind?

We will probably never figure this out
I am more willing to blame my inabilities then some quirk of nature. Just got my mind to wondering about the effects. I am going to lean more towards form problems with trying to send a bullet between gusts.

Steve
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