TOPIC: Firearm Injuries
Sub-topics:
· Hand guns – revolvers and pistols – and their basic component parts and function
· Rifling. The cartridge and the bullet. The mechanism of firing a hand gun. Rifling marks. The velocity of the bullet and the kinetic energy used to produce the firearm wound
· 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
Notes for the topic: A handgun is a short-barrelled firearm that can be held and used with one hand. The two most common handgun sub-types in use today are revolvers and semi-automatic pistol . A pistol is a type of single-barrel handgun. A revolver is a repeating handgun that has a revolving cylinder containing multiple chambers and at least one barrel for firing. The purpose of the rifling is to impart a rotational spin to the bullet along its longitudinal axis to stabilize the bullet's flight and prevent its tumbling end over end in the air. Spinning of the bullet prevents yaw. A projectile possesses kinetic energy that may be expressed according to the following formula: KE=MV2/2, where M is the mass of the bullet and V is the velocity of the bullet. This formula readily explains the much greater influence of velocity of the bullet over mass of the bullet in determining kinetic energy. In all the varieties of contact wounds soot, powder (burning, burned, and unburned), carbon monoxide, any metallic fragments possibly produced from the bullet, and vaporized metals from the bullet, primer, and cartridge case are deposited in and along the wound path.
Hand guns – revolvers and pistols – and their basic component parts and function
A handgun is a short-barrelled firearm that can be held and used with one hand. The two most common handgun sub-types in use today are revolvers and semi-automatic pistols, and other handguns like machine pistols and derringers.
A pistol is a type of single-barrel handgun. A revolver is a repeating handgun that has a revolving cylinder containing multiple chambers (each holding a single cartridge) and at least one barrel for firing.
Basic Parts of a Handgun:All modern handguns have three basic groups of parts.
Action: The action, also known as the trigger group, contains the parts that fire the cartridges. Several types of actions are used in modern handguns.
Frame: The frame is a metal housing that also serves as the handle (grip) of the handgun. All other parts are contained within it or connected to it.
Barrel: The barrel is the metal tube that the bullet travels through. The handgun barrel is much shorter than a rifle or shotgun barrel because the gun is designed to be shot while being held with one or two hands, rather than being placed against the shooter's shoulder.
Repeating handguns (revolvers and semi-automatic pistols) hold more than one round of ammunition. A revolver uses a cylinder to store the ammunition, and a semi-automatic pistol uses a removable magazine that fits in the grip.
Rifling: The cartridge and the bullet. The mechanism of firing a hand gun. Rifling marks. The velocity of the bullet and the kinetic energy used to produce the firearm wound
Rifling refers to the helical groovings that are machined into the internal (bore) surface of a gun's barrel, for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting. The purpose of the rifling is to impart a rotational spin to the bullet along its longitudinal axis to stabilize the bullet's flight and prevent its tumbling end over end in the air. Spinning of the bullet prevents yaw.
Cartridge is rifled firearm ammunition, which can be loaded into the chamber of the gun and can discharge the bullet on being fired . It is made up of two segments—cartridge case and bullet.
Cartridge case – It is an elongated metallic cylinder made up of cupronickel alloy, and its length varies with each type of gun. This has two ends, a flat and closed end, base.
Bullet – It has got a conical shape and four components; a body , a flat base, a pointed tip , and a lead core within.
By virtue of its movement, a projectile possesses kinetic energy that may be expressed according to the following formula: KE=MV2/2 , where M is the mass of the bullet and V is the velocity of the bullet. This formula readily explains the much greater influence of velocity of the bullet over mass of the bullet in determining kinetic energy. Doubling of, the bullet mass will only double the kinetic energy. Doubling the velocity, however, will quadruple the kinetic energy and hence the extent of firearm wounds. The bullet passes through the tissue and crushes the tissue in its direct path while the kinetic energy also causes the surrounding tissues to be radially flung away from its path. This action creates a temporary cavity with a diameter very much greater than the bullet itself, This temporary cavity only exists for 5-10 msec from its rapid growth to collapse, but it undergoes a series of pulsations and contractions before it disappears and leaves the permanent wound path. Thus, the amount of tissue involvement in the final wound is not only a function of the actual bullet path but also the effects of the temporary cavity.
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
Low-velocity bullets (less than 1500 ft/ sec, handgun bullets) produce a direct path through the tissue with only a small temporary cavity that plays no significant role in the amount of wounding. For damage. to occur to a body structure or organ, it must be struck directly by the handgun bullet. Gunshot wounds are classified according to the range of fire into four main categories:
Contact wounds, Near-contact wounds , Intermediate-range wounds and Distant or indeterminate-range wounds
• Contact wounds: Contact wound means that the weapon muzzle was held against directly contact with the skin at the time the weapon was discharged. Separate consideration is given to contact wounds occuring over bone because of their special characteristics. In all the varieties of contact wounds soot, powder (burning, burned, and unburned), carbon monoxide, any metallic fragments possibly produced from the bullet, and vaporized metals from the bullet, primer, and cartridge case are deposited in and along the wound path. It is the skin appearance that gives the different classifications of these wounds. Contact wounds are subdivided into the following categories:
Hard-contact wounds: Hard-contact wounds result when the muzzle of the weapon is held very tightly against the skin so that the skin is indented and envelops the muzzle at the time of discharge. The margins of the entrance are blackened and seared by a combination of the flame and soot emanating from the muzzle and being driven into the wound. All of the gases and other materials from the muzzle enter the wound. Often, there is little to indicate that one is dealing with a contact wound except for the careful examination of the immediate margins to detect the searing and soot. The further dissection of the wound will disclose powder grains and soot within the wound path. If the wound overlies muscle, red discoloration may be seen from the absorption of carbon monoxide to produce both carboxyhemoglobin and carboxymyoglobin.
Loose-contact wounds: In loose-contact wounds the muzzle is held completely against the skin but lightly so that it does not indent the skin. The gases preceding the bullet, as well as the bullet itself, indents the skin. This produces a very slight space between the muzzle and the skin through which the gas escapes and carries with it soot that is deposited in a concentric zone around the entrance. In contrast to the hard-contact wound, this soot can be easily wiped away and is not burned into the skin. A few loose particles of powder may appear about the wound but will not be embedded in the skin. Powder, vaporized metals, soot, and carbon monoxide will be driven into the wound path.
An intermediate-range wound that has a great deal of soot deposition because of the relatively close distance between the skin and the muzzle. The wound has distinct powder tattooing. If the muzzle of the weapon had been somewhat nearer to the skin, a near-contact wound would have resulted, and no powder tattooing would have been present. Anytime that one can identify any powder tattooing not just loose powder grains lying on the skin, one is dealing with an intermediate-range wound.
The wound of an intermediate-range with scattered powder tattoos surrounding the entry hole: The maximum distance at which powder tattooing will occur is dependent upon the ammunition involved and what form of gunpowder it uses. In order to determine the muzzle-to-skin distance, the actual weapon and ammunition of the same brand, preferably from the same box, must be used to re-create the powder tattoo pattern.
The wound of an indeterminate-range has no secondary effects from the powder or other cartridge materials. There is only the physical interaction of the skin and the projectile.
Angled-contact wounds
Incomplete-contact wounds: These wounds represent a variant of angled-contact wounds, but in this case the incomplete contact of the muzzle with the skin results because the surface of the body where the weapon is placed is not completely flat. The resulting zone of blackened skin can be in any location relative to muzzle of the weapon. These wounds are most common seen in cases of self-inflicted gunshots to head. As a practical matter, these wounds are not of much concern, and the ability to determine that the wound is a contact wound is the important matter.
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