Exterior Ballistics - Wind Effects

Started January 16, 2017.
Updated at random.

Competitive shooters have been using this old wind rose for decades.
I got to wondering how accurate it is for modern high BC long range bullets.
WindVector


The Hornady 4  DOF exterior ballistics program accounts for drop, aerodynamic jump, and wind drift.  It also outputs directly to a file that Office Spreadsheet can read. 

In 4DOF I created an accurate profile of my 6.5 Creedmoor firing 143 grain Hornady ELDx bullets and tested the results on targets to 1,000 yards on the range.

Next, using Hornady's 4DOF,  I entered 10 mph wind at 15 degree intervals all the way around the shooter, and stored the results in 100 yard increments to 1,000 yards in the spreadsheet.
I did a little simple number crunching to combine all of the data into bullet impact points in minutes of angle horizontally and vertically away from the point of aim for each range with each wind.   The plot below is simplifed to show only 1,000 800 and 400 yard impact deflections as predicted  by Hornady 4DOF.

Wind Deflection Plot 143 ELDx 10 mph 1,000 800 400 yds


Finally, I took that spreadsheet data into AutoCAD and created a true to scale drawing of the results.
This represents what the wind will do to a bullet very accurately, and it's qute remarkable in that it looks very little like the old style wind rose.
Another (at the time unremarkable) feature of this plot is the vertical symetry around the point of aim.  Notice wind from 12 O'Clock supposedly moves the point of impact about -0.17 MOA and wind from 6 O'Clock moves the POI about +0.16 MOA?  Jump to the AB Mobile solutions and you will see that the entire impact plot is shifted vertically because head wind and tail wind are not symetrical!

I ran some similar plots in JMBALLISTICS and that's where things go 'interesting' ... so I purchased Applied Ballistics Mobile to attempt to resolve the discrepancies. 

DETOUR

As I got more involved in these plots, I found that JMBALLISTICS and Hornady's 4DOF ballistics programs have a big difference from Advanced Ballistics Mobile in the amount of wind drift this load experiences at 1,000 yards, particularly with respect to a wind from 9 O'Clock where it adds to spin-drift.

The data below is for Hornady 143 ELDx, 2652 fps, 2473 ft ASL, 71.5F, 1-8" twist.

Raw 4DOF output:
Wind 10MPH < 90,   1000 yds; Total Come Up:  +29.10, Total Wind Drift (MOA):  5.93
Wind 10MPH < 270, 1000 yds; Total Come Up:  +29.68, Total Wind Drift (MOA): -6.99

Raw JMBallistics output:
Wind 10 MPH <90,   1000 yds; Drop (MOA): -29.1, Windage (MOA): 5.2
Wind 10MPH < 270, 1000 yds; Drop (MOA): -29.1, Windage (MOA); -5.2

Raw Advanced Ballistics Mobile ouptput:
Wind 10MPH < 90,   1000 yds; Come Up moa*: U29.80, Windage moa*; R6.15
Wind 10MPH < 270, 1000 yds; Come Up moa*: U30.50, Windage moa*; L7.35

The plot below is my latest update replacing the Hornady 4DOF above with AB Mobile data below.  The AB Mobile app allows for selecting wind by the O'Clock method, and I found it easier to plot using the O'Clock value, so there are plots every hour (30) below vs. the 15 used above.

Here is an article by Bryan Litz about the Hornady 4DOF but I don't see where the differences he referrs to should be responsible for the difference I see in this discussion.




10 MPH AB  Mobile
To test for altitude sensitivity between my home range (2473 ft AGL) and Sea Level standard atmosphere I ran the following in AB Mobile:

If the target is at Mud Lake (DA: 2473), in Spring (Temp: 71.5F) then;
10 MPH < 3 O'Clock = U29.50, R6.00 | 10 MPH < 9 O'Clock = U30.20, L7.20

If the target environment is changed to sea level std. atmo. (DA: 0ft, Temp: 59F), then;
10MPH < 3 O'Clock = U29.40, R5.95 | 10 MPH < 9 O'Clock = U30.10, L7.15

The difference is negliglible for 1,000 yards.
The new wind plot shows an entirely different set of effects from Aerodynamic Jump and Spin Drift.
I trust Brian Litz to get ballistics right.  With that said, I went back through my DOPE and found the AB Mobile solutions matched real world conditions I had recorded over many days, firing locations, weather and range.  So I'm going to rely on AB Mobile solutions from here on.

Now back to the original discussion.

END DETOUR