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

#1
02-10-2012, 06:02 PM
 Gold Member Join Date: Jan 2011 Posts: 607
9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

I'm getting 52" of drift with a 9 o'clock vs. 33" of drift with a 3 o'clock wind using bullet flight on my iPhone. I'm assuming these numbers are different due to spin drift with a right hand twist but didn't think the difference would be that great. Am I doing something wrong? This was a 5mph wind @ 1000yds.
#2
02-10-2012, 06:24 PM
 Gold Member Join Date: Sep 2009 Location: Washington Posts: 782
Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Not sure why you're getting that. I get the same going either way on mine, only difference is -2moa or 2moa depending in wind position. I'm using bullet flight fte on my ipod
#3
02-10-2012, 06:28 PM
 Platinum Member Join Date: Feb 2007 Location: Townsend, Montana. Posts: 8,652
Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Something is wrong. Probably an input parimeter or a lead installed like a moving target app. Spin drift at 1000 should be more like 5 to 7 inches. Go over all your settingand see if one needs zeroed out.

Jeff
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#4
02-10-2012, 08:21 PM
 Platinum Member Join Date: Nov 2008 Posts: 1,087
Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

52-33=19
divide by 2 = 9.5"

Seems a bit much for Spin drift even with Coriolis thrown in as well. But I just punched the numbers into "Shooter" for a .308 with 155gn bullet and they are similar for a Northern Hemisphere location when SD and CE are taken into account.
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#5
02-10-2012, 09:23 PM
 Gold Member Join Date: Jan 2011 Posts: 607
Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Both spin drift and coriolis are being accounted for. Also this was 180gr. Fusion ammo B.C.=.478 going 2950
#6
02-10-2012, 11:37 PM
 Gold Member Join Date: Jan 2011 Posts: 607
Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Another interesting fact is that 52" of drift @ 5mph becomes 94" when 10mph is plugged in. I would think it would be 104". Ive gone through this app and can't find what could be causing these readings. If I take spin drift off and coriolis off then the drift is the same whether it be a 3 o'clock or a 9 o'clock. It does make sense that with a no wind hold the bullet would drift right (and low) with a right hand twist so I could understand a different hold when dealing with a 90* or a 270* wind. I just have a hard time believing it would be as great as what it is telling me.
#7
02-10-2012, 11:59 PM
 Platinum Member Join Date: Oct 2009 Location: Thunder Basin, WY Posts: 1,788
Re: 9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

Quote:
 Originally Posted by shortpants Another interesting fact is that 52" of drift @ 5mph becomes 94" when 10mph is plugged in. I would think it would be 104". Ive gone through this app and can't find what could be causing these readings. If I take spin drift off and coriolis off then the drift is the same whether it be a 3 o'clock or a 9 o'clock. It does make sense that with a no wind hold the bullet would drift right (and low) with a right hand twist so I could understand a different hold when dealing with a 90* or a 270* wind. I just have a hard time believing it would be as great as what it is telling me.
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".

Every app that I've personally looked at also suggests that a 10 mph wind doubles the effect of a 5 mph wind. Hmmmn.....??
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