Practical Pathology of Gunshot Wounds

Archives of Pathology & Laboratory Medicine, Sep 2006 by Denton, J Scott, Segovia, Adrienne, Filkins, James A

Rifles are subdivided into lever action, bolt action, and semiautomatic. Lever-action rifles, such as the Winchester Model 1894 seen in countless Western films, use an extension of the trigger guard as the lever. When the lever is moved down, a spent cartridge casing is ejected; when it is moved back up a new cartridge is chambered and the hammer recocked. Bolt-action rifles, such as the Remington Model 700 hunting rifle, secure a cartridge in the firing chamber by a bolt, which also houses the firing pin.When a shot is fired, the shooter must manually pull the bolt back to allow the spent cartridge casing to eject and a new cartridge to move into position. Pushing the bolt forward slides the new cartridge into the firing chamber and recocks the firing mechanism. Semiautomatic rifles, such as the M1 Garand, operate on principles similar to semiautomatic handguns.

IDENTIFYING ENTRANCE, EXIT, AND GRAZE WOUNDS

Shooting someone in the back that is running away from you versus shooting someone in the chest while defending yourself from an attack highlights the importance of differentiating entrance wounds from exit wounds. In criminal law, correctly differentiating between the 2 can mean the difference between first-degree murder charges and a possible death sentence or justifiable self-defense and no charges. Fortunately, the application of a few basic concepts will usually permit an accurate differentiation of entrance wounds from exit wounds.

Typical entrance wounds are ordinarily round in shape with a circumferential margin of abrasion surrounding the defect produced by the bullet (Figure 1, A and B).4 The margin of abrasion is a scraping or scuffing of the skin caused by the bullet as it pushes inward. The margin of abrasion may be concentric or eccentric. When a bullet penetrates the skin nose on, it produces a concentric margin of abrasion-that is, a ring of scraped skin of uniform thickness-because it enters perpendicular to the skin. When the nose of a bullet penetrates the skin at an angle, it produces an eccentric margin of abrasion, that is, a ring that is thicker in 1 area. The thick area of an eccentric margin of abrasion indicates the direction from which the bullet came. In addition, the thicker the margin the shallower the angle of the bullet was as it struck the skin.

Atypical entrance wounds are irregular in shape and may have tears at the margins.5 This type of entrance wound usually occurs when a bullet loses the spin imparted to it by the rifling in the barrel of the gun. Instead of traveling in a tight spiral, the bullet "wobbles" as it strikes the skin often imparting a D-shaped appearance to the wound. Atypical entrance wounds can be caused by a weapon that malfunctions or by defective ammunition, but more often they result from ricochets or the passage of a bullet through an intermediate target, such as an automobile window, before it strikes the body. The bullet may, in turn, impart velocity to the intermediate target causing it to strike the skin producing atypical abrasions around the entrance wound. Another type of atypical entrance wound occurs when the muzzle of a gun is in contact with the skin over a bony surface, such as the skull or sternum (Figure 2). When the gun is fired, it discharges gases directly from the muzzle into the wound along with the bullet. The gases penetrate into the subcutaneous tissue, where they expand causing the skin around the entrance wound to stretch and tear. The tears or lacerations radiate out from the central defect giving the wound a stellate or star-shaped appearance.