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9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

 
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  #8  
Old 02-11-2012, 12:24 AM
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Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

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Originally Posted by SBruce View Post
That does seem excessive. The numbers I've seen generated from Exbal suggest only a 3" effect at 1000 yds due to Coriolis alone. Spin Drift (as near as I've been able to gather) could perhaps be 3 times that amount in some cases.?.........Still, we're only talking about maybe 12" difference at 1000 yds, not 19".

...??
Remember you have to half the drift difference to compare it against SD and CE.
SD is added in one direction and subtracted from the other as it is always to the right with a RH twist barrel.
So the 19" difference is actually 9.5" total drift due to SD and CE.
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Old 02-11-2012, 01:53 AM
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Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

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Originally Posted by Topshot View Post
Remember you have to half the drift difference to compare it against SD and CE.
SD is added in one direction and subtracted from the other as it is always to the right with a RH twist barrel.
So the 19" difference is actually 9.5" total drift due to SD and CE.
AhHaaaa, that makes sense. Good point. Thanks for that insight!

If I'm understanding correctly, in theory we'd have 9-10" right at 1000 under no wind for SD and CE, dead on with a 3:00 wind and 20" right with a 9:00 wind, assuming the wind alone accounts for 10" drift at 1000.

That seems to also explain why when we were shooting at 1000 yds (with a 4:00 wind that increased speed as the day went on) that our shots continued to climb higher than expected (as the wind increased) and the wind didn't blow them off as much as expected.
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Old 02-11-2012, 05:40 PM
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Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

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Originally Posted by SBruce View Post
AhHaaaa, that makes sense. Good point. Thanks for that insight!

If I'm understanding correctly, in theory we'd have 9-10" right at 1000 under no wind for SD and CE, dead on with a 3:00 wind and 20" right with a 9:00 wind, assuming the wind alone accounts for 10" drift at 1000.

That seems to also explain why when we were shooting at 1000 yds (with a 4:00 wind that increased speed as the day went on) that our shots continued to climb higher than expected (as the wind increased) and the wind didn't blow them off as much as expected.
Yes, the first part is correct for that scenario.

Not sure about the second part with the shots "climbing higher"? That could be due to a vertical component of the wind?
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Old 02-11-2012, 11:16 PM
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Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Thanks for clarifying that Top Shot that makes since. I ran some different numbers to help make sense of it.
A no wind hold puts me 9.2" right
A 1mph 3 o'clock wind puts me .7" right
A 1mph 9 o'clock wind puts me 17.8 right

A 1 mph wind has an effect of roughly 8.5" of drift
A 3 o'clock wind you subtract 8.5 from 9.2 since the wind is pushing the bullet back against the spin drift almost canceling eachother out which gives you .7

For a 9 o'clock wind you have to add 9.2 and 8.5 since they are working together which gives you 17.7 (close enough). Not sure why the .1 difference but understand the answer to my question now.

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Old 02-11-2012, 11:57 PM
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Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

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Originally Posted by Topshot View Post
Yes, the first part is correct for that scenario.

Not sure about the second part with the shots "climbing higher"? That could be due to a vertical component of the wind?
It sure could be, I haven't yet totally proved to myself that horizontal wind causes vertical drift, but it seems to be a more recognized phenomenon here lately. I even started this thread a while back to try and get some answers.
Wind Direction changes our Vertical Impact......Fact or Myth?


In the video How to Dope the Wind Beyond Belief, one guy talks about how the spinning bullet drops less with a right wind, and drops more with a left wind. Just as spin drift "rolls" the bullet right (RH twist), it supposedly also makes it drop less or more depending on the wind direction. He stated that for every 3 or 4 minutes of drift, there would be about 1 minute of elevation change.??

When I get my LRR all load picked and dialed in at 1000, I intend on testing this theory for good. I can shoot 1000 yds east and then turn right around and shoot 1000yds west in no wind conditions. Then on another day, when there is a slight wind from the north or south, I will shoot the same test at the same distances and try to see just how much the wind changes my vertical........problem is, on different days there will be a different pressure or temperature to deal with too. If Coriolis affects the vertical (like the program says) that's 6 inches vertical that would have to be accounted for. Might take a long time and alot of ammo before I can totally prove this theory right or wrong. Expensive too at $5 a crack and a new barrel after $1500 rounds.

In addition to the chart in the above link, here's another one that has been posted here on LRH lately. Even if it's never proved, it's interesting to discuss.
None of my programs address this phenomenon at all.
Attached Thumbnails - Click to View Larger
9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???-wind-drift.jpg  
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  #13  
Old 02-12-2012, 12:24 AM
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Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Not sure if I am reading your chart properly but there seems to be a big change in POI when the wind is going from indication points #6 and #7. Also the same large change in POI when the wind is going from points #12 and #1.
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Old 02-12-2012, 12:33 AM
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Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Yes there is, hadn't noticed that before.?? That's weird.

This chart isn't quite so drastic. I didn't make either one of these, just passing them on for sake of conversation. I don't yet shoot 1000 yds and beyond often enough to have my own interpretation of what's really happening out there.
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9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???-wind-chart_1.jpg  
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