This section lists the parameters displayed in the
Current Data panel, giving a qualitative description of each
parameter to assist data selection. The mathematical
handling of the parameters is detailed in Part 2 of this
document, together with additional information and tabulated
data.
|
Parameter
|
|
Description
|
Units
|
|
QUARRY
|
Probable
X-speed
|
1
|
The velocity at which the quarry crosses the
firer's line of sight: this affects the required
lead and swing. The quarry's component of velocity
towards or away from the firer is assumed to have
little effect.
|
m/s
|
|
Maximum entry energy
|
2
|
The kinetic energy density lost by a pellet
penetrating through the most resistant area of
feathers and skin. Note that 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.
|
/mm2
|
|
SHOT
|
Material
density
|
3
|
The effective average density of the pellet
material. The density of some materials commonly
used or considered for shot is given in Appendix
C.
|
g/cc
|
Pellet
diameter
|
4
|
The average diameter of the shot. The program
does not cater for duplex (i.e. multiple) pellet
sizes. Appendix C lists standard shot sizes.
|
mm
|
Shot mass
total
|
5
|
This is used together with the shot material
density and pellet diameter to compute the number
of pellets (which is then displayed at the bottom
of the Current Data panel.)
|
g
|
|
VELOCITY AND CHOKE
|
|
Measured velocity
|
6
|
The velocity of the shot cloud measured at some
measurement range (see next parameter) from the
muzzle. Note, the declared velocity almost
invariably relates to the leading pellets in the
shot cloud: if used, this value will give an
overestimate of effectiveness. The measured
velocity together with measurement range is used to
compute the effective muzzle velocity (which is
then displayed at the bottom of the Current Data
panel.)
|
m/s
|
|
Measurement range
|
7
|
The distance from the muzzle at which the
velocity is measured. If the velocity measuring
device comprises two detectors which derive
velocity from the time taken for the pellets to
transit, then the measurement range is
approximately the distance from the gun muzzle to
midway between the two detectors.
|
m
|
|
Drag factor
|
8
|
This parameter allows for distortion or surface
roughness of the spherical pellets. A value of 1
has no effect, less than 1 corresponds to drag
reduction, and greater than 1 corresponds to an
increase in drag. The value must be obtained by
comparing the observed downrange velocity with that
predicted by the program, and its value will
generally lie in the range 0.90 to 1.15. In the
absence of trajectory instrumentation, the drag
factor should be assigned a value of 1.000.
For example:
Giblin & Compton give the following standard
ballistics for a single #6 (2.6mm diameter) lead
pellet.
If muzzle velocity = 400m/s then
at 40yards (36.6m), velocity = 189m/s.
To match this in the program, the drag factor is
reduced by 3% from 1.000 to 0.970.
|
|
|
Choke
|
9
|
The modification to the pattern (lateral spread
of the shot cloud) produced by profiling the
internal muzzle of the gun. The program
conveniently uses the traditional measures of
choke, i.e.:
|
|
Choke name
|
% in 30in circle @ 40yds
|
|
|
Cylinder
|
40
|
|
|
Improved cylinder
|
50
|
|
|
Quarter
|
55
|
|
|
Half
|
60
|
|
|
Three-quarter
|
65
|
|
|
Full
|
70
|
|
and
|
Other
|
1 to 99
|
The 'Other' choke provides for non-standard
patterns. Most guns are assessed for patterning
ability using lead shot, and it should be noted
that some natures of shot material or construction
will tend to pattern differently to lead shot from
the same gun. The ammunition construction,
particularly under- and over-wads, propellant
selection, compression and crimp, will further
affect patterning. The combination of each
particular gun and new ammunition should be checked
for pattern: in the program: use the measured
rather than the nominal choke.
For example:
If the barrel is marked 'half choke'
but on firing your new ammunition you measure a
55% pattern at 40 yards (i.e. quarter choke) ,
then use quarter choke in the program.
Note: the pattern size does not grow linearly
with range. The program follows the observation of
Giblin & Compton that pattern size is more
linearly related to time of flight. For this reason
it is vital that when measuring the pattern
percentage in a 30inch (76.2cm) circle, the range
is exactly 40yards (36.6m)
|
|
|
ACCURACY
|
The four 'errors' listed here will together
affect the achievable accuracy. The supplied
'accuracy datafiles' and the text below give only
advisory starting values for these 'errors'. Their
proper values need to be obtained by detailed
measurement.
|
|
Basic error
|
10
|
A measure of the limiting accuracy of the firer
as achieved when unhurriedly shouldering the gun
and firing at a stationary target. The declared
value is a standard deviation. A novice game shot
is likely to produce a basic accuracy of around
1°, whereas an experienced shooter will
generally reduce this to 0.4° or less
|
degs
|
|
Swing error
|
11
|
A measure of the limiting accuracy of the firer
as achieved when unhurriedly shouldering the gun
and firing at a stationary target. The declared
value is a standard deviation. A novice game shot
is likely to produce a basic accuracy of around
1°, whereas an experienced shooter will
generally reduce this to 0.4° or less
|
5
|
|
Lead error
|
12
|
This significant inaccuracy is also measured as
a standard deviation, but only in the direction of
flight of the quarry. The shooter aims ahead of the
quarry, but can misgauge this required lead. The
error is taken to be some percentage of the
required lead calculated using the quarry crossing
speed and pellet time of flight: in the field a
value of 20% is very good, and around 80% for a
poorer shot.
|
%
|
|
Range error
|
13
|
In firing shotgun, mis-estimation of range
affects the application of correct lead, thereby
supplementing the lead error. In the field a value
of about 20% is likely for an experienced shot, and
perhaps as great as 80% for the inexperienced
shot.
|
%
|
|
FIELD POLICIES
|
|
Retriever
|
14
|
Is a retrieving dog being used, yes or no? The
availability of a retrieving dog affects the
ability to bag some birds which initially are not
killed outright.
|
Yes/no
|
|
Wildfowl over water
|
15
|
Is the quarry a species of wildfowl flying over
water, yes or no? A downed wildfowl which still has
the use of one leg may avoid being brought to bag
by swimming and diving. This effect is considered
by the program in computing retrievability with and
without a retrieving dog
|
yes/no
|
|
Policy ranges
|
16 to 19
|
The distribution of ranges at which the shooter
expects to fire at game. The program automatically
guards against irrational policy ranges.
Note that if shortened ranges are achieved by
decoying or other field techniques, the crossing
speed of the quarry may be much reduced, and so the
crossing speed parameter should be adjusted to
suit.
|
m
|
