azide styphnate or other mixture
which avoid corrosive action of ful-
minate or mercury. The primer in-
dented by the firing pin, shows a
very definite embossed pattern. This
pattern not only shows the marks of
the pin but in different weapons of
the same make, the pin strikes the
primer in a slightly different position
giving an additional point of com-
parison.

EXTRACTOR AND EJECTOR
MARKINGS

No discussion of the cartridge as
it concerns the firearms examiner, can
be complete without reference to ex-
tractor and ejector markings. All
automatic weapons and those in
which ejection of the spent cartridge
is by lever, pump, or bolt action,
have a small part which engages the
base of the cartridge and withdraws
it from the chamber prior to ejecting
it. As the cartridge is firmly wedged
in the chamber due to gas pressure
at the time of firing, the ejector or
extractor, leaves an indentation in
the soft brass. As in the other points
of comparison above, the location
and mark of indentation is quite
individual to the type of weapon
from which the cartridge was fired.
Frequently the shape and pressure of
the extractor or ejector leaves an
engraving peculiar to itself alone. We
see therefore, that a cartridge may be
identified by its caliber, its type, the
markings on the case left by the
chamber, the markings left on the
base by the breach block or bolt,
the markings on the primer by both
firing pin and breach. and the marks
left on the cartridge base rim by the
ejector or extractor.

Perhaps a few remarks on what

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EN

Page Thirty-four

is meant by ‘‘caliber’’ and “‘gauge”’
may be enlightening to those un-
familiar with the terms. ‘‘Gauge’’ is
used mostly in describing the bore
diameter of a shotgun or of an old
type muzzle loading musket. In an-
cient weapons, the bore was made
to fit leaden balls of a given weight.
These shot went so many to the
pound. In one size of ball there
might be ten to the pound, while in
another size there would be 12 or
perhaps a third size would have
sixteen balls to the pound. The arms
manufacturers arbitrarily applied to
the guns they were making a number
of the same value. So, if a musket
was bored to accommodate a ball
whose weight was one-sixteenth of
a pound, he would call the musket
a “16 Gauge.’”’ This method of de-
termining the size of smooth bore
weapons is still carried along in de-
scribing shotgun bore diameters.

The term “‘caliber’’ was also used
in conjunction with smooth bore
weapons of a later date. A pistol
which fired a ball having a diameter
of one-half inch or .50 inches, was
called a “50 caliber.’’ The caliber of
a weapon indicates its diameter in
hundredths of an inch. Continental
arms use the metric system in de-
scribing bore diameters thus a metric
caliber of 6.35 millimeters is equival-
ent to a nonmetric caliber of .25
inches.

In the past the caliber followed
quite faithfully the actual diameter
of the weapon. Now, however, there
are small discrepancies and the near-
est accepted caliber is quoted. In one
weapon which is called a ‘.38 cali-
ber’ the actual bore diameter is only
.36 inches.

Going back to shotguns, it may be
mentioned that the muzzle of one
barrel in double barreled shotguns is
frequently tapered to a smaller apert-
ure, though the remainder of the
barrel remains standard gauge. This
modification of muzzle aperture is
arbitrary with each manufacturer and
is intended to create a smaller pattern
of shot at a given distance, and
thereby increase the density of the
cone of fire. The following is a table
of different chokes and the percentage
of shot which will be contained in
a thirty-inch circle at a distance of
30 yards:

Type of Choke Percentage of Shot
in 30 inch Circle

Full choke See TS)

Modified choke 65
Improved cylinder __ .55
Cylinder bore

(no choke) : 45

There will be greater carrying
power where a full choke barrel is
used as the constriction of the barrel
will hold the shot bunched together
for a greater distance before dispers-

a

”

ing. The “‘shot pattern’’ of a shotgun
is properly speaking, a ballistic prob-
lem and an instance will be discussed
further on in this article where eyj-
dence of this type was of paramount
importance in a case of attempted
murder.

DETERMINING GAUGE OF SHOTGUN
FROM PELLETS

Dr. Otto Mezger, writing in
Chemiker-Zeitung, September 27,
1930, discussed a method of deter-
mining the gauge of a shotgun from
pellets which had been fired but not

SBIJECTIVES

Schematic of the light paths in a comparison
microscope. Front section of left hand bullet
and rear section of right hand bullet are
brought together in eyepiece for comparison.

deformed by striking a hard object
with force. The doctor suggested that
a number of pellets would be forced
along the side of the smooth bore
barrel as they were discharged and
would thus acquire a ‘‘flattening”’ on
one side. This ‘‘flattening’’ would be
limited by the inner curvature of the
barrel so the pellet would acquire a
similar curvature. Using a number of
gauges cut to different standard shot-
gun sizes, the doctor placed the pellets
in contact with the curved surfaces
and photographed them illuminating
them on the far side. The gauge
which showed the least light between
itself and the pellet, was considered
to be the proper shotgun diameter
of the weapon from which the pellets

THE SHOULDER STRAP