SIPMEUMRICINL? IPO CIMILISS,
AS POLICE OFFICERS are often faced
with the investigation of cases involving
the use of shot guns a few notes regarding
this type of arm may be of interest and
value.

We often hear of a shot-gun having a
“full choke” or a “cylinder bore” barrel,
but outside of knowing that the full choke
barrel makes a “tighter” pattern and car-
ries a little further, the average person
does not know a great deal about the sub-
ject.

In the manufacture of shot-gun barrels,
there are generally four types of barrel.
The “cylinder bore” is usually made with
the muzzle of the same diameter as the
remainder of the bore. In the three other
types, the muzzle has been squeezed in
to give an orifice of smaller diameter than
the barrel. These types are ‘Improved
cylinder”, “Modified Choke” and “Full
Choke”. These different types are not
arbitrary sizes of barrels, and may vary
from one manufacturer to another even
though the guns are of the same gauge.

The relative diameter of the muzzle is
arrived at by test, and depends upon the
particular weapon making a certain pat-
tern on a target at a given distance.

The measurement of shot-gun chokes
is usually carried out at a distance of 30
yards, and the target is a 30-inch circle,
that is, a 30-inch circle is applied to the
area of greatest shot concentration. If
only 45% of the shot are within the 30-
inch circle, the barrel is a “Cylinder Bore”.
If 55% of the shot are in the circle, then
it is an “Improved Bore”. If 65% of the
shot are concentrated in the ring it is a
“Modified Choke’, and 75% within the
prescribed area indicates the barrel is
“Full Choke’.

On shot-gun shells there will often be
found two numbers such as “3” and “6”.

Page Seventy-four

These can be interpreted to mean that the
charge of powder in the shell develops
a pressure equal to that of 3 drams of
black powder, and that the shot is Number
6. The letters “‘c” or “ch” indicate chilled
shot.

To ascertain the diameter of a specific-
ally numbered shot, it is merely a matter
of subtracting the number of the shot
from the constant number 17. Thus if we
have a shot numbered 6, we subtract 6
from 17, which leaves 11. This denotes
the diameter of the shot in one hundredths
of an inch, so in this case it would be
eleven one hundredths or in decimals .11
inch.

It is also interesting to know that “drop
shot” is made from pure lead, while the
shot known as “chilled shot” contains a
percentage of antimony to harden the lead.

ENb Point’ INDEPENDENT OF CHARGE

Another and little known fact concern-
ing shot or spherical projectiles, is that
for every diameter of sphere there is a
definite “end point’” or maximum range,
irrespective of the amount of propellant
or power used to drive it.

This fact was discovered by a French
captain of artillery while conducting bal-
listic experiments with ancient type field
pieces using spherical cannon balls. He
found that after increasing the charge be-
hind the ball to drive it a certain maxi-
mum range, any extra powder in the
charge did not materially increase the
range. He then figured out the mathe-
naatics of this phenomenon, and discovered
the rule, which is as follows; Multiply
the constant 2200 by the diameter of the
shot, and the result will be the extreme
range in yards. Thus taking our No. 6
shot, which we find has a diameter of .11
inches, we find that the result indicates
a maximum range of 242 yards, regardless
of the amount of propellant used. Of
course if the amount of powder is less
than the maximum charge the range will
drop in like proportion.

The old method of determining shot-
gun gauges may be of some interest.
sriefly it consisted merely of the number
of lead balls to the pound each of which
would fit the bore of the arm snugly. Thus
a 12-gauge shot-gun would be a weapon
which would accommodate a sphere of
lead of one twelfth of a pound. Similarly

a 10 gauge gun, would have a projectile
of one tenth of a pound, and so on.

However due to the “choking” of shot-
guns, such a plan could not be continued, |
and manufacturers established other arbi-
trary sizes. Thus now a 10 gauge shot-
eun accommodates a ball of two twenty-—
sevenths of a pound, and a 12 gauge takes
a ball of one seventeenth of a pound,
while 201% balls to the pound fit the 16
gauge arm.

os

PHOTOGRAPHIC NOTES
by CONST. G. S. PEARSON
SINCE PHOTOGRAPHY is steadily

being recognized as an important part of
general police investigation and no longer
a specialized study, it behooves the aver-
age police officer to have a nodding
acquaintance with the bare essentials re-
quired to take pictures under any and
all circumstances. There are a number
of good books published, which deal
with the subject exhaustively and any
serious student can avail himself of
plenty of carefully compiled information.
This article is designed to study a few of
the angles of photography met with most
often, and an effort will be made to
explain them in a straightforward manner,
so that the taking of pictures under
adverse circumstances will not present a
problem or require a good deal of study
on the subject.

First, a few words about film. Such
rapid strides have been made in recent
years in the manufacture of new types
of film that any person not practising
photography in the last few years will be
in the same position as an amateur start-
ing out to learn something of the art.
Colour film is rapidly becoming some-
thing more than just a dream and in the
next five years will take the place of
black and white in a good many instances.
However, for ordinary police work, it
will be a long time before colour film will
be simple enough to use. At the moment
the colour temperature of the light source
is of paramount importance and exposures
are critical, requiring an exposure meter,
ete. Ordinary film for black and white
photography has made some long strides
in regard to speed and exposure latitude,
and we may. now take advantage of these
new features. Panchromatic film such
as Kodak's Super XX and Ansco’s Super
Pan Press as well as being sensitive to
all the colours is very fast and both are
good film to use under adverse circum-
stances. The film ratings are usually
supplied with the film and since these
films are sensitive to all colours, they
must be processed in complete darkness.
However, if it is thought necessary to
process the film by observation, (should
the requirements not render it possible
to control the exposure) a fast ortho-
chromatic film may be used. As this film
is not sensitive to red colour, it may be

THE SHOULDER STRAP