Range and Wind Uncertainty in Field Target

 

From observing and talking to top shooters it is evident to me that on the non-discipline shots ranging and wind reading are the two most important factors in consistently hitting a KZ.   But how much does the ability to range accurately and read the wind increase the chances of a hit?  Is there a way to quantify range and wind uncertainty?

Bryan Litz has written several books about accuracy and precision in long range shooting.  

He takes a very methodical approach and isolates factors that impact accuracy and precision.  In light of those factors, his writing and consulting assists shooters in making intelligent choices about where to spend money on equipment and their practice time.  His books are well written and worth a read.

Having read his books, I became interested in what he calls his Weapons Employment Zone (“WEZ”) analysis found in his Applied Ballistics analytics software.  I was curious of his software could model range, wind, and other uncertainty effects with airguns to evaluate the impact of  ranging and wind estimation errors on hit percentages.  After some communications with Applied Ballistics, it was confirmed to me that the software could model at our field target ranges.

While this is not a review of the software, I think it is worth mentioning a few things out of the gate about it.

  • This is a PC program and the user interface is not very slick.   The focus is clearly on function.
  • It only uses the G1 and G7 drag models.  
  • There is a bullet database with custom drag curves, but this is not helpful for us airgun shooters since there are no pellets in the database. I selected the G1 model in the software.
  • As a tool for making range cards, it does not allow the user to get results in clicks.
  • It is not a product designed around the specific needs of air rifle shooters.

With that out the way, my primary aim was to get statistical results so that I could compare trends based on basic inputs about the ballistics of pellets.

As an initial foray into this, I decided to limit the analysis to two commonly used pellets:  the JSB 10.3 and the JSB 7.9.   While there are other pellets in common currency in FT, the purpose of this initial analysis is to find trends in the data and draw some general conclusions at 20fpe and 12fpe power levels.

I am certain that upon careful inspection and thought that the technical-minded in our FT community can raise questions about the approach and results.   To that end, any and all critiques are welcome. However, all I am doing is using the Applied Ballistics Analytics software to get the results.  So the critique will either be on the variables I used or the operation of the software.  I can only defend my choice of variables, so let us start with the basic ballistics variables I used:

  • JSB 7.9g
    • BC .021 (Chairgun)
    • Diameter .177″
    • Length: .216″
    • FPS: 822 (11.9fpe) with SD of 5
  • JSB 10.3g
    • BC .031 (Chairgun)
    • Diameter .177″
    • Length: .246″
    • FPS: 932 (19.9fpe) with SD of 5
  • Wind 7mph at 9 o’clock to shooter
  • Ranging SD +- 1, 2, 3, 4 and 5 meters
  • Wind speed SD +- 1, 2, 3, 4, and 5 mph
  • Rifle capable of 1 MOA extreme spread
  • Target distance is 50 yards
  • Target  is 1.5″ circle

I had initially considered modeling 45, 50 and 55 yards using the 1.5″ KZ.   However, after starting the process and looking at the results from 45 and 55 yards, I concluded that the 50 yard analysis was representative and instructive at least for the last ten yards that we shoot.  Granted, under our rules we have the largest kill zones out past 45, but that is also where the wind and ranging challenges are most difficult.

The results of multiple calculations at the 50 yard target with the 1.5″ KZ are in the table below.   The Y axis is the range estimation error in meters (the software, oddly, does not allow one to set this in yards) and the X axis is the wind estimation error in MPH.   The software calculates a hit percentage based on the ballistics of the projectile.     In my analysis I focused on the range and wind effects and the relationship between those effects on hit percentages.

 

Based on an informal poll of Tar Heel Air Gun Club members, most Open and WFTF shooters say they are able to range to within 1 to 3 yards of a 50 yard target.   Hunter shooters indicated they could range within 3 to 5 yards of a 50 yard target.

Example 1:

  • 20fpe rifle with JSB 10.3’s;
  • Range SD 1 meter at 50 yards;
  • Wind SD of  3 mph;
  • then the hit percentage is 75.49.

Example 2:

  • 12fpe rifle with JSB 7.9’s;
  • Range SD 1 meter at 50 yards;
  • Wind SD of  3 mph;
  • then hit percentage is 55.27.

Example 3:

  • Hunter piston at 12fpe
  • Range SD 4 meters at 50 yards;
  • Wind SD 2 MPH
  • then hit percentage is 35.44.

Example 4:

  • Hunter piston at 12fpe
  • Range SD 2;
  • Wind SD 1;
  • then hit percentage is 82.42.

The results assume a rifle/shooter combination capable of producing a 1 MOA group.   This is an incredibly huge assumption.  However, we are simply looking at the impact of range and wind uncertainty on the hit percentages applied to that (big) assumption to find trends in the data and see if any useful conclusions can be drawn.   Do not read the results to mean that any given shooter will  have the hit percentage shown in the tables.  Also implicit in the analysis is that the wind is constant.   We know that in the real world wind is often not constant in direction or speed.

Conclusions:

  • Range uncertainty results in vertical errors.   Wind uncertainty results (primarily) in horizontal errors. A shooter should seek to reduce those uncertainties because
    • A perfectly placed shot in the vertical axis has more room for horizontal error induced by wind uncertainty; and
    • A perfectly placed shot on the horizontal axis will allow more room for vertical error induced by range uncertainty.
  • The ballistics of a 10.3 JSB at 20fpe gives more room for error in ranging and wind estimation errors at every similar combination of wind and range SD’s than the JSB 7.9 pellet at 12fpe.
  • The drop off in hit percentages after 2 standard deviations for both wind and range is remarkable with the 7.9 grain pellet at 12fpe compared to the 10.3 grain pellet at 20fpe.
  • The major advances in hit percentages in Hunter division (shooting at 20fpe) will come from the ability of the shooter to range a 12x scope and use other ranging methods such as bracketing to reduce range uncertainty.
  • A Hunter division shooter must be adept at reading the wind to offset ranging errors inherent in the optics of parallax ranging a 12x scope.
  • Hunter piston shooters who shoot around 12fpe have the worst case scenario of range uncertainty and 12fpe ballistics.
  • Assuming the average WFTF and Open shooter can consistently range to within 1 or 2 yards on a 50 yard shot, hit percentages are increased with better wind reading.