In order to
interpret gunshot wounds, a certain basic knowledge of firearms and ammunition is necessary. There are five general categories of small
arms: handguns, rifles, shotguns, submachine guns, and machine guns. There are four basic
types of:
1. Single-shot
pistols
2. Derringers
3. Revolvers
4. Auto-loading
pistols (automatics)
A single-shot
pistol has one firing chamber integral with the barrel, which must be loaded manually each time
the weapon is to be fired.
Derringers are a variant of single-shot pistols.
Derringers are small pocket firearms having multiple barrels, each of which is
loaded and fired separately. The traditional derringer has two barrels.
The revolver is the most common type of handgun in the
United States. Revolvers have a revolving cylinder that contains several
chambers, each of which holds one cartridge. The cylinder is rotated
mechanically so as to align each chamber successively with the barrel and
firing pin. The first revolver was produced by Samuel Colt in 1835–1836.
There are three types of revolvers, the most common of
which is the “swingout”. On pressing the cylinder latch, normally found on the
left side of the frame and pushing the cylinder to the left, the cylinder swings
out, exposing the chambers. Each individual chamber is then loaded with a
cartridge. The cylinder is then swung back into the frame, engaging the
cylinder latch. The weapon is now ready to be fired. After discharge of all the
cartridges, the cylinder latch is pressed and the cylinder is swung out. In break-top revolvers, the frame is hinged at the
rear such that, on release of a top catch, the barrel and cylinder swing down,
exposing the back of the cylinder for loading. The opening action will also
eject empty cases from the cylinder. This form of weapon is relatively uncommon
in the United States, but is the traditional form of revolver in Great Britain.
The solid-frame revolver is the oldest form of revolver, dating back to Colt’s
original weapons. In this weapon, the
cylinder is held in the frame by a central pin, around which it rotates. The
back of this cylinder is never exposed completely by either “swinging out” or
“breaking open.” Each chamber in the cylinder is loaded individually through a
loading gate on the right side of the frame. The hammer of the weapon is
typically pulled back to half cock, and the cylinder is then manually rotated
so that a chamber is aligned with the loading gate. A cartridge is inserted.
The cylinder is then manually rotated to the next chamber and a second
cartridge is inserted. This procedure is continued until the cylinder is
completely filled. After the weapon is discharged, the cylinder has to be
manually rotated again and aligned with the loading gate, and each cartridge is
ejected through the gate using the ejector rod. Revolvers may be either single-action or double-action
types. In single action revolvers, the hammer must be cocked manually each time
the weapon is to be fired. Cocking the hammer revolves the cylinder, aligning
the chamber with the barrel and the firing pin. Pressure applied to the trigger
then releases the hammer, discharging the weapon. In double-action revolvers a
continuous pressure on the trigger revolves the cylinder, aligns the chamber
with the barrel, and cocks and then releases the hammer, firing the weapon.
Most double-action revolvers may be fired in a single-action mode. Many
single-action revolvers have a “half-cock” notch in the cocking hammer that
lies between the position of “full cock” and “fired.” The purpose of the
half-cock notch is to catch the hammer if it accidentally slips from the thumb
as it is being manually cocked. Many individuals incorrectly consider the
half-cock notch a safety position and will carry weapons on “half cock.” Dropping
a weapon when on half cock may cause the hammer to disengage, fly forward, and
discharge the weapon. Some single-action revolvers will fire from the half-cock
position if the trigger is pulled. Ruger single-action revolvers equipped with
a safety bar do not have a half-cock notch. The cylinder of a revolver may
rotate either clockwise or counterclockwise. This difference has resulted in a
number of deaths among individuals playing Russian roulette, in which an
individual loads one chamber of a revolver and spins the cylinder.
Auto-loading or automatic pistols make up the fourth
category of handguns. The term “automatic pistol” is a misnomer, as this form
of pistol is an auto-loader in which the trigger must be pulled for every shot
fired. Regardless of the correct terminology, however, these weapons are
invariably called “automatics” or just “pistols.” These pistols use the forces
generated by the fired cartridge to operate the mechanism that extracts and
ejects the empty cases, loads the fresh cartridge, and returns the mechanism
into position to fire the next round. The term “clip” is often used
synonymously with the term “magazine.” In fact, a clip is a device designed to
facilitate the loading of a number of cartridges into a magazine, however, most
people use the terms interchangeably. There are five methods of operation of automatic
pistols: blow-back, delayed or retarded blow-back, blow-forward, recoil, and
gas. Only two of these methods are currently in widespread use: blow-back and
recoil. In a blow-back action, the pressure of the gas produced by combustion
of the powder forces an unlocked slide to the rear, thus starting the cycle of
extraction, ejection, and reloading. In a recoil-operated automatic pistol, the barrel and
the slide are locked together at the moment of firing. As the bullet leaves the
barrel, the rearward thrust of the propellant gas on the cartridge case starts
the barrel and slide moving to the rear. After a short distance, the barrel is
halted, and the locking device is withdrawn from the slide. The
slide then continues to the rear, ejecting the fired case and starting the
reloading cycle. Many of the newer double-action
automatic pistols have a thumb piece on either the slide or frame which
externally resembles the usual safety lever but is in fact a decocking lever. It
may be on the left side, ambidextrous or reversible. When this thumb piece is
pushed down, the hammer falls. The weapon will not discharge, however, as the
thumb piece locks the firing pin and/or rotates a steel surface between the
hammer and the firing pin to prevent contact between the two. In some weapons,
the decocking lever now functions as a safety and the weapon will not fire as long
as this device is down. Other automatic pistols do not have any manual safety
but only a decocking lever, e.g., Sig-Sauer.
The Sig-Sauers, as well as most of the newer quality
automatics, are equipped with a firing pin safety (lock). This internal device
locks the firing pin in place preventing forward movement and thus accidental
discharge. In order to fire the weapon, the trigger must be pulled back in
order to disengage this safety. Some pistols have a device that tells whether
the chamber contains a cartridge. This may be a protruding pin at the rear of
the slide or just protrusion of the extractor. Some automatic pistols have
magazine safeties. Preparing an automatic pistol to fire involves two steps.
First, the loaded magazine is inserted into the grip. The slide is grasped,
pulled rearward, and released. A spring drives the slide forward, stripping a
cartridge from the magazine and loading it into the firing chamber. The weapon
is now cocked and ready to be fired. If the weapon has a manually operated
safety, the safety may now be applied and the weapon carried in a
cocked-and-locked mode.
A rifle is a firearm with a rifled barrel which is
designed to be fired from the shoulder. The types of rifles commonly
encountered are single-shot, leveraction, bolt-action, pump-action, and
auto-loading. A single-shot rifle has one firing chamber integral with the
barrel which has to be manually loaded each time the weapon is fired. A
lever-action rifle has a lever beneath the grip which is used to open the rifle
action, to extract the cartridge case, and, in closing the action, to insert a
fresh cartridge in the firing chamber and to cock the gun. In a bolt-action
rifle, a handle projects from a bolt. Pulling back and pushing forward on this
projection causes the bolt to extract and eject a cartridge case and then to
insert a new cartridge while cocking the gun. The slide-action rifle uses the
manual movement of a slide under and parallel to the barrel to open the action,
extract and eject a cartridge, load a fresh cartridge, and cock the weapon. In auto-loading or semi-automatic rifles, the weapon
fires, extracts, ejects, reloads, and cocks with each pull of the trigger using
the force of gas pressure or recoil to operate the action. A fully automatic
rifle is one that, on pulling the trigger and firing the weapon, utilizes the
force of gas pressure or recoil to eject the fired case, load the next round,
fire it, and then eject it. This cycle is repeated until all the ammunition is
used or the trigger is released. One of the common fallacies about
assault rifles is that the wounds they produce are more severe than those due
to ordinary centerfire rifles. The intermediate cartridges used
in assault rifles possess significantly less kinetic energy than a regular
centerfire rifle cartridge. A submachine gun or machine pistol is a weapon that
is designed to be fired from either the shoulder and/or the hip; is capable of
full-automatic fire; has a rifled barrel, and fires pistol ammunition. It is
often incorrectly called a “machine gun.” A machine gun is a weapon that is capable of
full-automatic firing and that fires rifle ammunition. It is generally
crew-operated, but some forms may be fired by single individuals. Most machine
guns have the ammunition fed by belts. Rifles, handguns, submachine guns, and
machine guns have rifled barrels; that is, spiral grooves have been cut the
length of the interior or bore of the barrel.
The best example of confusing caliber designation and
the one most significant to the forensic pathologist involves the .38 Special
and .357 Magnum cartridges. Weapons chambered for these calibers have barrels
with the same bore and groove diameters. Bullets loaded in each of these
cartridges have identical dimensions. The .357 Magnum revolver chambers and
fires all .38 Special ammunition, although a weapon chambered for a .38 Special
cartridge cannot ordinarily chamber and should never use the .357 Magnum cartridge.
The .357 Magnum cartridge case is, in fact, the .38 Special cartridge case
lengthened and loaded with additional propellant. Except for the difference in
the length of the cartridge cases, all other physical dimensions are the same
for both calibers. The term “Magnum,” is used to
describe a cartridge that is larger and produces higher velocity than standard
cartridges. In the case of shotgun ammunition, it may or may not be larger but
does contain more shot than the standard shell.
A small-arms cartridge consists of a cartridge case, a
primer, propellant (gunpowder), and a bullet or projectile Blank cartridges are sealed with paper disks instead
of a bullet or have a crimped neck. Dummy cartridges have neither a primer nor
powder. Some dummy cartridges contain inert granular material that simulates
powder. Cartridge cases are usually made
of brass, a composition of 70% copper and 30% zinc. Less commonly, they are
made of steel or aluminum. The main function of the cartridge case is to expand
and seal the chamber against rearward escape of gases when the cartridge is
fired. When a brass cartridge is fired in a weapon, the gas pressure produced
by the burning of the propellant expands the case tightly against the walls of
the chamber. If the brass is tempered to the correct hardness, it will spring
back to approximately its original dimensions and make the case easy to
extract. If the brass is too soft, it will not spring back and will make
extraction difficult. If the brass is too hard — that is, brittle — it will
crack.
Cartridge cases are classified into five types
according to the configuration of their bases:
1. Rimmed
2. Semi-rimmed
3. Rimless
4. Rebated
5. Belted
Rimmed cartridge cases have an extractor flange that
is larger than the diameter of the cartridge case body. The letter R is added
after case length numbers in the metric system of caliber designation. Semi-rimmed
cartridge cases have an extractor flange that is larger in diameter than the
cartridge case body, but they also have a groove around the case body just in
front of the flange. The metric designation for these cartridges is SR. Rimless
cartridge cases have an extractor flange whose diameter is the same as that of
the cartridge case body and also have a groove around the body of the case in
front of the flange. In the metric system of caliber designation, no letter is
used for this type of cartridge case. A rebated cartridge case has an extractor
flange that is smaller than the diameter of the case. A groove around the body
of the case is present in front of the flange. The metric designation is RB. A belted cartridge case has a pronounced, raised belt
encircling the cartridge case body in front of the groove in the body. The
diameter of the extractor flange is immaterial. The metric designation is B. When
a weapon is fired, the firing pin strikes the center of the primer cup,
compressing the primer composition between the cup and anvil and causing the
composition to explode. The vents in the anvil allow the flame to pass through
the flash hole(s) into the cartridge case and thereby igniting the propellant. The
bullet is that part of the cartridge that leaves the muzzle of the firearm when
it discharges. Bullets were originally lead spheres. Lead bullets are made out
of lead to which antimony and/or tin have been added to increase the hardness
of the alloy. These bullets are lubricated with grease or lubricating compound
to help prevent leading (lead fouling) of the barrel. Some lead bullets are
covered by an extremely thin coating of copper or copper alloy. There are four general configurations of lead bullets:
roundnose, wadcutter, semi-wadcutter and hollow-point. A roundnose lead bullet
has a semiblunt, conical shape and a flat or bevelled base. The wadcutter bullet,
which resembles a cylinder of lead, has a base that may be either bevelled or
hollow. Wadcutter bullets are designed primarily for target use. The
semi-wadcutter configuration is that of a truncated cone with a flat tip and a
sharp shoulder of bore diameter at the base of the cone. The lead hollow-point bullet
has a semi-wadcutter configuration with a cavity in the nose that is designed
to facilitate expansion of the bullet upon impact with the target.
For most of this century, flintlock and percussion
weapons have been only of historical interest. In the past few decades, there
has arisen an interest in replica black-powder arms. Numerous weapons of this
type have been sold. These range from precise replicas of historical weapons to
totally new designs. Most of these weapons are manufactured abroad. They are
available as flintlock and percussion muskets, rifles, and shotguns and
percussion revolvers.
Acknowledgements:
The Police
www.politie.nl and a Chief Inspector – Mr. Erik Akerboom
©
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