FIREARM INJURY I
Ballistics
Gun
Rifled - handguns , rifles , snipers
Smooth barreled - shotguns
Muzzleloader
Handguns consist of four basic types:
Single-shot pistols
Derringers
Revolvers
Auto-loading pistols ("automatics")
Parts of a handgun
barrel,
frame or receiver
the slide or the cylinder.
Cartridge
outer casing
projectile ( bullet)
propellent
primer ( source of ignition )
Range
hard contact
loose contact
incomplete contact
near-contact
intermediate
indeterminate
Character of firearm injuries
Loss of substance
Presence one or two wound by the same bullet
Powder marks ( blacking , burning , tattooing)
Beveling in flat bones
Sub-topics:
Handguns – revolvers and pistols – and their basic component parts and function
Firearm is a specialized device designed to propel a projectile ( shot / bullet /missile ) by the expansive force of gases generated as a result of combustion of the propellant (power) at its base in a closed space.
Handguns are designed to be fired by one hand without support from the body. Handguns are the easiest firearms to carry as they are lighter in weight and can be more quickly and easily brought into action. They are, however, far less accurate over longer distances due to their relatively short barrels and, therefore, are most often considered primarily as defensive weapons.
Pistol—A firearm that has a chamber as part of the bar-rel and is typical of semi-automatic handguns.
Revolver—A firearm that has a number of chambers ina cylinder that rotates and the bullets revolved on an axis; during successive fir-ing, a chamber rotates and aligns with the barrel.
Broadly speaking, the three main parts of a handgun will be barrel, frame or receiver, and either the slide or the cylinder. For single shot pistols this will be the frame, barrel and stock or grip.
Revolvers use a rotating cylinder which is advanced by a hammer being cocked manually or by a trigger pull. The first of the three basic parts of a handgun that apply to a revolver is this cylinder. The cylinder holds the ammo, and rotates to bring a live round under the hammer.The next part is the frame. As with any gun, the frame or receiver is where the barrel attaches, and any other parts needed for fire are installed. On a revolver we’ll find the trigger and hammer assembly here, along with the cylinder and grips, making it the heart of the entire gun.The last of the three major components of a pistol is the barrel. Pinned or screwed into the frame, the barrel also has the forcing cone which guides the bullet into the bore and ensures the round is perfectly centered. Barrels can be very short, or very long, and will be fitted with sights.
A pistol is a hand-operated firearm having a chamber integral with or permanently aligned with the bore.As with all pistols, the frame is a main part of a semi automatic pistol. Along with the trigger and other fire control parts, it also holds the magazine, slide and barrel.In common with other types of handguns, the barrel is a major part of a semi automatic pistol. The barrel may be pinned or screwed to the frame, or attached with a link with a removable pin through the frame, although there are less common methods that are also used.The slide is the last major pistol part to consider here. The slide can take many different forms, but always rides around the barrel and cycles with a fired round to eject a spent round and load a fresh one from the magazine. Front and rear sights are also mounted to the slide.
Rifling. The cartridge and the bullet. The mechanism of firing a handgun. Rifling marks. The velocity of the bullet and the kinetic energy used to produce the firearm wound.
On the major advances of improving the accuracy , spiral grooves on the inside of the guns barrel causes the projectile to spin about its long axis in a motion leading to gyroscopic stabilisation as seen in a rugby throw. It improves the aerodynamic properties , allowing it to go much faster and with much better precision and accuracy. In short , rifling gives a straight course,preventing it from unsteady movements as it travels in the air.
Rifling involves Making grooves where some part of metal is removed to create depression leaving the high areas called lands. The twist may be dextrorotatory ( American firearms ) or levorotatory . An alternative type of rifling that doesn't use spirals but uses polygons are also becoming popular these days because of faster manufacturing.Instead of grooves and lands , they consist of hills and valleys.
Cartridge is a self-contained unit that includes an outer casing , projectile ( bullet) , propellent , primer ( source of ignition ) . Only the projectile is fired from the gun and the remainder of the spent cartridge is ejected from the weapon. The bullet is a projectile loaded into a cartridge and which ejects out. It can be made with both soft metals like lead and hard alloys like bronze. They are covered either partially or completely by a metal jacket.
The mechanism of firing of a bullet begins from loading the cartridge into the chamber. After the trigger is released the hammer having a firing pin forcefully strikes the percussion cap hitting the primer. The primer detonates and ignites power which is an igniting mixture . The combustion causes the gas to expand in the cartridge. The gas propels the bullet out with a great force. Eventually the bullet escapes the barrel and the loud sound is produced. The gun may be Manual , semi automatic or automatic .
Muzzle energy is the kinetic energy of the bullet as it is expelled from the muzzle of a firearm. The bullet causes injury by transferring it's kinetic energy (KE). Severity of the damage is proportional to amount of Kinetic energy and density of the tissue.kinetic energy increases in proportional to increase in velocity squared. Greater the velocity, greater is the wound potential. If a projectile doesn't exit the body , then all It's KE is transferred to the tissues and if it exits , then only some of its kinetic energy has been transferred to the tissue.Wounding potential depends on the transfer of energy to the tissues. The resistance of the tissue cause bullet energy to shed the surrounding structure.The bullet creates a temporary wound cavity which disappears leaving the permanent wound track.
When a bullet passes along the barrel of a gun , the softer metal of the bullet is distorted and shaped to match the lands and grooves of the barrel. One can tell the type of rifling used by studying the type of rifling , number of groves, direction of twist and the twist rate . It produces Rifling marks . No two rifled barrels are identical even manufactured by the same manufacturer.
Range of fire and characteristics of fatal low-velocity rifled firearm wounds to the head and trunk: hard contact, loose contact, incomplete contact, near-contact, intermediate and indeterminate
The range of a fire can be determined by the through study of the gunpowder residues.the greater the distance from the target, the farther the gunpowder residue will spread.
In hard contact ,If the skull gets fractured, the wound of entrance shows
a punched-in (clean) hole in the outer table, and inner table shows a bevelled crater; whereas reverse will be the effects at the exit (if present), i.e. punched-out opening is produced at the inner table and bevelled opening at the outer table.on the trunk , the imprint of the muzzle of the gun may be found as patterned abrasion on the skin around the wound. This results from the great distension of the subcutaneous tissues from the entry of gases which forces the surface against the muzzle.Singeing of the hair may be present due to the escape of hot gases.
In loose contact , corona formation can be seen due to expelled hot soot. The gases escape and it doesn't produce an eruptive or explosive type of wound.
carbon monoxide combines with the haemoglobin and myoglobin of the tissues of the track and thereby imparts pinkish colouration to the interior of the wound track and the adjacent tissues.
If the contact is incomplete , the gas may leak out one if the side and form a peach shaped blackening .
In the intermediate range ,The entrance wound at such ranges is usually circular or oval, and the margins are driven inwards by the passage of missiles. The size of the hole is rarely equal to the size of the diameter of the missile.After the bullet passes through the skin, the skin tends to return to its former size and edges of the wound contract and the resulting hole is smaller than the diameter of the missile.
In indeterminate range , the reduced velocity may result in instability of the flight path. The bullet may begin to wobble and yaw and may even tumble, i.e. turn end-over-end. If the bullet strikes the body during this phase, the impact may be sideways or even backwards. The wound accordingly will be irregular.