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# Vertical component of wind drift

#8
04-08-2003, 10:27 AM
 Posts: n/a
Re: Vertical component of wind drift

4MESH,

The vertical component of wind drift is not a result of pressure differential from aerodynamic forces. It is in fact a result of gyroscopic precession.

Len,

Harold Vaughn and I differ on only a few things. The vertical component of wind drift is one of them. If you look at Harold's example at 100 and 200 yards you'll notice he tries to make a case for the vertical component to be linear. The examples that he gives for shooting in a varying crosswind component and then doing a least-squares function and plotting the resultant angle to estimate gyroscopic stability is valid. My six PPC with a 14 twist barrel shoots right at 18 degrees with a 67.5 gr. bullet. The Wolf with an 11 twist barrel will shoot about 26 degrees when a least-squares function is plotted at 100 yards.

As we all know, wind drift is a squared function, not linear. If one were to continue Harold's theory well past 200 yards, let's say to 1000 yards, there would be a massive reduction in the angle plotted because Harold believes the vertical component is linear and wind drift is exponential.

The truth is, in practical observation, we see a significant angle (15-20 degrees) at 1000 yards, very similar to what 4MESH describes. Mathematically, we describe gyroscopic precession with an exponential curve, yaw of repose is one example.

I believe the observations of 4MESH are correct, I don't believe he has identified the actual forces involved. There are several explanations that I would offer as to why Harold missed the mark on this element. One, he did not have the equipment and a controlled environment to test at extremely long ranges, if he did he would have noted that the vertical component was not linear. Second, much of Harold's research was done with the equipment that fired at significantly higher launch angles than the typical 1000 yard rifle. To understand this issue from a practical sense, you must have a rifle that will shoot with almost zero vertical error. Without this tool, any attempt to measure will be lost in the noise of other overlapping error sources.

Remember that Harold offers data only to a very short distance relative to what most guys on this site are shooting. His ascertion that the angle is strongly correlated to gyroscopic stability is correct.

I have observed on many occasions past 1000 yards a vertical component relative to the actual wind drift in a ratio of 1 to 4, with bullets on the edge of stability, 1 to 6. [img]images/icons/wink.gif[/img]

[ 04-08-2003: Message edited by: S1 ]
#9
04-08-2003, 05:12 PM
 Platinum Member Join Date: Jun 2001 Location: Palmer, Alaska Posts: 2,539
Re: Vertical component of wind drift

Sam, thanks for your insight. Looks like some more testing's in order now. [img]images/icons/smile.gif[/img] Here's a teaser from Harolds book. You might have to save the images to be able to zoom in closer to read the text.

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Brent Moffitt
#10
04-08-2003, 08:04 PM
 Silver Member Join Date: Dec 2002 Posts: 374
Re: Vertical component of wind drift

S1, so you contend that the bullet changes direction because of gyroscopicly applied/affected forces. I have another set of conditions to run past you but I'll have to get back on that.

Brent, for those people without the book, you're gonna have to post that in a higher res. Blowing it up is pretty problematic.
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If you have something that you disassemble and reassemble enough times, sooner or later, you'll have two!
#11
04-08-2003, 08:41 PM
 Platinum Member Join Date: Jun 2001 Location: Palmer, Alaska Posts: 2,539
Re: Vertical component of wind drift

I saved it and enlarged it on Microsoft Picture and Fax Viewer "OK", but it is a little hard to read, but manageble, the other programs didn't work as well.

When I send the images to Sony Imagestation so I can post them they are obviously reduced in size automatically, the original was 896 x 1408 at 244KB, now it's 286 x 450. I don't know how to do it any better than that. I can email you them if you need me to, they should stay at the higher res.
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Brent Moffitt
#12
04-08-2003, 08:51 PM
 Silver Member Join Date: Dec 2002 Posts: 374
Re: Vertical component of wind drift

I've got the book so I don't need them. Thanks anyhow. What'd ya think of the collet dies? Did ya notice the marks where the taper changed so the one resized the neck on a taper? That other case you saw was Ken Markles invention. Pretty cool huh. That's a 416-6.5 that shoots pretty darn good at 1000.
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If you have something that you disassemble and reassemble enough times, sooner or later, you'll have two!
#13
04-08-2003, 09:15 PM
 Platinum Member Join Date: Jun 2001 Location: Palmer, Alaska Posts: 2,539
Re: Vertical component of wind drift

Sorry I forgot all about it. It does look like it was alot of work. Why size the neck on a taper? The short little funky shouldered fella there looks interesting! Nice lookin rifle you got there too!

You sure are a handy kind a guy, the can do type, I like that! [img]images/icons/wink.gif[/img]
__________________
Brent Moffitt
#14
04-08-2003, 09:34 PM
 PUBLISHER Join Date: May 2001 Posts: 6,508
Re: Vertical component of wind drift

Followup question:

How much vertical rise or drop due to tail or headwind? Examples at 1,000 yards?
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