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# Calculating drop with head or tail wind?

#8
09-22-2009, 12:47 AM
 Official LRH Sponsor Join Date: Mar 2007 Location: Montana Posts: 2,925
Re: Calculating drop with head or tail wind?

Quote:
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
09-22-2009, 12:56 AM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,830
Re: Calculating drop with head or tail wind?

What was the distance?
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, 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.
#10
09-22-2009, 01:10 AM
 Official LRH Sponsor Join Date: Mar 2007 Location: Montana Posts: 2,925
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
09-22-2009, 10:03 AM
 Gold Member Join Date: Oct 2007 Location: Patagonia Mountains, Arizona Posts: 770
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.
#12
09-22-2009, 12:53 PM
 Platinum Member Join Date: May 2008 Location: South of Canada and North of Wyoming Posts: 6,068
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
#13
09-22-2009, 11:43 PM
 Official LRH Sponsor Join Date: Mar 2007 Location: Montana Posts: 2,925
Re: Calculating drop with head or tail wind?

Quote:
 Originally Posted by MontanaRifleman 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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To hunt... or not to hunt...? What a stupid question.

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