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# Aerodynamic Jump and Ballistic Solutions

#1
10-15-2013, 04:41 AM
 Junior Member Join Date: Mar 2012 Location: Denmark Posts: 12
Aerodynamic Jump and Ballistic Solutions

Most ballistic solution gadgets and ballistic software solutions, I have reviewed, do not correct for aerodynamic jump. The vertical bullet deflection caused by aerodynamic jump due to wind may be significant at long range. Bryan Litz has developed a very accurate estimation of aerodynamic jump, but, except for Rianov, nobody - to my knowledge - has incorporated aerodynamic jump into their solution. I wonder why!

This issue is of importance to me as I shoot long range in a very flat environment with high winds most of year. I would be grateful to hear from you regarding your solution to solving this problem. Thank you.
#2
10-15-2013, 06:53 AM
 Platinum Member Join Date: Aug 2003 Location: NC, oceanfront Posts: 4,226
Re: Aerodynamic Jump and Ballistic Solutions

It's called 'magnus effect'
External ballistics - Wikipedia, the free encyclopedia

By the time you did any calculations of it in the field, the conditions would likely change enough to negate results.
I've heard of compensation at pre-chosen values of conditions(many) by turning the scope in it's mount/reseting elevation level. This would work for competitors, given all conditions known/fixed up front.
#3
10-15-2013, 10:23 AM
 Junior Member Join Date: Mar 2012 Location: Denmark Posts: 12
Re: Aerodynamic Jump and Ballistic Solutions

The Magnus effect is even effecting a bullet in no wind conditions, as the rotational movement of the bullet causes airflows to create low pressure under the bullet relative to the top of the bullet (bullet viewed from the back), resulting in a downward force called “Magnus". I am not referring to the Magnus effect.
I am referring to “aerodynamic jump” as described in Bryan Litz’s book “Applied Ballistics for Long-range Shooting” – second edition, pages 75-83. A gyroscopic stable bullet will point its nose into the oncoming airflow (wind) and experience precession cycles, which are lop-sided, resulting in a vertical deflection of a constant angular value for the entire trajectory – thereby making aerodynamic jump a deterministic variable, which should be accounted for in the ballistic solution. I have 0.1 mill scope adjustments and at 300 yards, I am one clicks off in low wind conditions.
Bryan’s estimated jump (Y) is calculated as follows:
Y = 0.01 x SG – 0.0024 x L +0.032 MOA/MPH
Where
SG = Gyroscopic Stability Factor (Don Miller; and air density dependent)
L = bullet length in caliber (bullet length in inches/caliber)
Y is up for wind from the right (right twist)
Y is down for wind from the left (right twist)
In order to get vertical wind deflection(up or down), you must multiply Y by wind force in mph, for a deflection in MOA, which is subsequently adjusted for range in order to get vertical deflection in inches (or cm where I come from) at that particular range.
Ballistic solutions, which include spin drift at range already calculate SG and L, as well as air density, so including vertical “jump” adjustments into the solution, should be fairly simple, if horizontal wind deflection is already employed (direction and power of wind is entered into the ballistic solver).
Wind conditions where I live vary a great deal. Calm is 10 mph and windy up to 25 mph. With high winds and long range, the jump adjustments become an important part of the total vertical adjustment - sometimes 3 clicks and 400 yards.
I would be grateful to receive advice, as how to EASILY adjust for vertical jump caused by wind – without carrying a computer and spending precious time making calculations.
#4
10-15-2013, 02:35 PM
 Gold Member Join Date: Aug 2011 Location: Lynchburg, TN Posts: 785
Re: Aerodynamic Jump and Ballistic Solutions

I just usually give it a little Kentucky Windage.
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#5
10-15-2013, 03:16 PM
 Platinum Member Join Date: Jan 2004 Location: Blackfoot, Idaho Posts: 8,876
Re: Aerodynamic Jump and Ballistic Solutions

Frank,

It would have been better for me if you wouldn't have raised this question.

I knew that the into the wind was different than with the wind but didn't know it was readily calculable.

One more thing to worry about.

Is SG a straight forward calculation? If so, one could do a little better than what I've been doing which is combination of guess work and KY windage.
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#6
10-15-2013, 03:27 PM
 Platinum Member Join Date: May 2008 Location: South of Canada and North of Wyoming Posts: 6,068
Re: Aerodynamic Jump and Ballistic Solutions

Quote:
 Originally Posted by royinidaho Frank, It would have been better for me if you wouldn't have raised this question. I knew that the into the wind was different than with the wind but didn't know it was readily calculable. One more thing to worry about. Is SG a straight forward calculation? If so, one could do a little better than what I've been doing which is combination of guess work and KY windage.
I'm gonna pretend I didn't see this thread
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#7
10-15-2013, 04:58 PM
 Gold Member Join Date: Nov 2012 Location: Green River, Wyoming Posts: 539
Re: Aerodynamic Jump and Ballistic Solutions

Quote:
 Originally Posted by MontanaRifleman I'm gonna pretend I didn't see this thread
+1 ...

Oh boy . . . Definitely don't have any input on this one...

I'm happy this factor can be measured though, might need to check on the sanity of the guy who came up with that equation though . . .
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