Department for Environment, Food and Rural Affairs

QUARRY:
a program to assess the effectiveness of shotgun ammunition
against wildfowl and other quarry

APPENDIX B: SHOOTER ACCURACY

The four contributory parameters characterising shooter accuracy, as described in Part 1, the User Manual, are specified as standard deviations as follows (given with their units):

 

Basic error

… the basic shouldering and pointing of the gun,

(degrees)

 

Swing error

because target movement undermines the accuracy,

(time in sec's

 

Lead error

due to incorrect judgement of how far ahead to shoot,

(%)

and

Range error

arising from estimation of range.

(%)

The 'Basic error' is converted to radians within the program. The 'Basic error' and 'Swing error' are measures of aim distribution about the mean. However 'Lead error' is a measure of variability about the correct lead angle, given as a percentage of the correct lead. Similarly, 'Range error' is specified as a percentage of the actual range. These are used in the following first-order approximations to determine the contributions to total dispersion of aim. The first three terms are considered independent, but the errorRange term is due the supplementary effect of range estimation error upon the application of lead.

errorBasic

=ErrorBasicR

errorSwing

=ErrorSwingQ

errorLead

=ErrorLeadQtR

errorRange

=ErrorRangeQ (R/vR-tR)

where

error

= standard deviation, m

R

= range to target, m

Q

= target crossing speed, m/s

t

= pellet time of flight, s

v

= pellet velocity at range, m/

Eleven sample datafiles are provided representing shooter ability. The parameter values for each category -poor, fair, good, very good, super - vary according to whether the target is a clay pigeon or a gamebird. The 'perfect' category is the same for either target: this equates to a target fixed in the centre of the pellet pattern. The sample datafile parameter values are listed below, together with bag/hit rates predicted by the program for typical conditions (program repetition = 5000 shots per range). The values are advised here as being representative of the shooter accuracy errors; specific values may be obtained by direct measurement or by fitting the program results to observations from well-controlled trials.

Shooter Characteristics versus Gamebird

Error
Poor
Fair
Good
Very Good
Super
Perfect
units

Basic
1.0
0.8
0.6
0.4
0.2
0
degrees

Swing
0.05
0.04
0.03
0.02
0.01
0
seconds

Lead
80
50
30
20
10
0
percent

Range
80
50
30
20
10
0
percent

Bag rate*
5%
10%
23%
43%
85%
100%

 

* Lead #6 (2.6mm) shot at 400m/s. Mallard underside, 15m/s. Long-ranging.1/2 choke.
 

Shooter Characteristics versus Standard Clay Pigeon**

Error
Poor
Fair
Good
Very Good
Super
Perfect
units

Basic
0.05
0.40
0.30
0.20
0.10
0
degrees

Swing
0.025
0.020
0.015
0.010
0.005
0
seconds

Lead
40
25
15
10
5
0
percent

Range
40
25
15
10
5
0
percent

Bag rate*
14%
28%
52%
76%
95%
97%

 

* Lead #71/2 (2.3mm) shot at 400m/s. Clay pigeon at 30°, 15m/s. Long-ranging. 1/2 choke

** The program assumes that each clay pigeon only requires one striking pellet to break it: this is the limiting best case, as in practice the reliability to properly break depends on the characteristics of the manufactured clay pigeon. The standard clay pigeon targets of the supplied quarry datafiles are assigned zero entry energy: this renders them rather sensitive to impact, so the user may wish to impose a modest value (say 0.1-0.2 J/mm2) for their maximum entry energy.

These contributions to dispersion are then combined

error2x = error2Basic + error2Lead + error2Range + error2Swing

error2y = error2Basic + error2Lead + error2Range

where x and y are respectively parallel and perpendicular to the target path as seen by the shooter. These total dispersions of aim are then used to drive a random Gaussian generator, sampled to determine the aimpoint of every simulated firing.

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Published 22 December 1998
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