Abstract
Caliber: The caliber of a handgun or rifle is typically described as the diameter of the bore, although this can sometimes vary depending on how the diameter is measured. For example, a 0.38 bullet refers to a bullet that can be fired along a bore that measures 0.38 inches in diameter. The caliber is expressed in inches in the United States (e.g., 0.45 inches) or millimeter (mm) in other countries (e.g., 9 mm).
Definitions
Caliber: The caliber of a handgun or rifle is typically described as the diameter of the bore, although this can sometimes vary depending on how the diameter is measured. For example, a 0.38 bullet refers to a bullet that can be fired along a bore that measures 0.38 inches in diameter. The caliber is expressed in inches in the United States (e.g., 0.45 inches) or millimeter (mm) in other countries (e.g., 9 mm).
Bullet Design: Traditional bullets are made of lead, a relatively soft material that expands on impact and increases damage to the intended target as more energy is imparted. Harder bullet materials, such as lead alloy, copper, bronze, and steel, limit this mushrooming effect on impact and can therefore penetrate deeper into tissues, but may not transfer as much energy if they completely traverse the target.
(a) Jacketed Bullet: At velocities greater than 2000 feet/second (ft/sec), lead bullets begin to strip and deposit metal as they travel down the barrel, increasing the probability of jamming. To avoid this problem, a “jacket” of a harder metal such as copper or zinc can either partially or completely enclose the softer lead core. In addition, the jacket provides stability to the missile and prevents fragmentation of deformation on impact. Civilian hollow-point and soft-point bullets are only partially jacketed, leaving the lead core exposed at the tip, which can then flatten out or mushroom on impact. Hunting rifle bullets are not jacketed and deform or fragment on impact, causing extensive tissue damage. An unjacketed bullet can cause up to 40 times more tissue damage than a jacketed bullet. Military bullets, constrained in design by the Hague Convention, are completely surrounded by a metal jacket (“full-metal jacket”), thereby preventing deformation upon impact.
(b) Hollow-Point Bullet: These missiles deform on impact and increase tissue damage. They are prohibited by the Geneva Convention for military use but are common in civilian use (Figure 11.1).
(c) Scored Bullet: Scoring of the bullet promotes fragmentation on impact, which results in increased tissue damage (Figure 11.2).
(d) “Black Talon” Bullet: The missile is covered with a copper jacket, which on impact peels back to form six sharp petals. These sharp edges can injure the exploring finger of the surgeon during attempts to remove the bullet. PDX 1 bullets are similar and are used by law enforcement in the United States (Figure 11.3 AD).
(e) PTFE (Teflon)-Coated Bullet: Teflon-coated bullets are designed to reduce the wear on the barrel and to decrease the chance of ricochet, and are more likely to penetrate bulletproof vests (popularly called “cop killers”). Armor-piercing designs, in which the bullet core is made of a hard substance such as depleted uranium or steel, are sometimes coated in Teflon and are not available for civilian use.
(f) Explosive Bullet: The bullet tip contains a small cavity filled with a small amount of explosive and explodes upon impacting a hard surface, such as bone. It often fails to explode and there is a risk of subsequent explosion during manipulation by the surgeon.
Figure 11.2 Bullet scoring promotes fragmentation on impact and increased tissue damage.
Figure 11.3 A–D Victim with gunshot wounds with PDX 1 bullets. Left forearm X-ray with resultant fracture of the radius and ulna (A). Bullets removed from the victim. The copper jacket peels back into six sharp petals upon impacting tissue, causing more tissue damage. The sharp petals may cut the exploring finger of the surgeon during the operation (B). Patient shot with PDX 1 bullet, resulting in massive liver injury (C). Bullet recovered intraoperatively. Note the sharp pedals that increase the tissue damage (D).
Bullet Velocity refers to the velocity of the missile at the muzzle of the gun and plays a critical role in the amount of inflicted tissue damage. The kinetic energy of missiles is determined by the mass of the projectile and its velocity. However, the degree of tissue destruction is not always proportional to the speed of the missile. The damage is proportional to the energy released into the tissues. Often the missile passes through the tissues without any major release of energy and results in only modest damage. Ballistics studies have shown that an AK-47 bullet releases its maximum energy only after traveling 25–30 cm into the tissues. If this bullet travels through a thin anatomical structure (e.g., the forearm), without hitting a bone, it might cause fairly limited damage.
Low-Velocity Projectiles
Low-velocity bullets (<1000 ft/sec or <340 meters [m]/sec) are commonly used in civilian firearms (handgun 9 mm at 280 m/sec, handgun 0.45 in at 255 m/sec). These bullets cause damage by direct crushing and laceration of tissues in the path of the missile. This path of destruction is referred to as the “permanent cavity.” Secondary injuries can occur as the bullet fragments or impacts bone, converting them into secondary missiles (Figure 11.4, Figure 11.5 A,B, Figure 11.6 A,B ).
Figure 11.5 A,B Radiological appearance of non-fragmented and not deformed low-velocity bullet (A). Bullet recovered at operation (B).
Figure 11.6 A,B Bullet fragmentation. Radiological appearance (A) and fragments after surgical removal (B).
The entrance wound is often characterized by an “abrasion ring” that develops at the edges of the skin defect and is typically round in appearance. This is caused as the bullet abrades the epidermis at the edges of the bullet path, leaving a reddish-brown circumferential ring on the damaged skin. This ring may develop irrespective of range, but it does not appear on palms, soles, axilla, and scalp. In comparison to entrance wounds, exit wounds generally tend to be larger and more irregular in shape. As a bullet travels through the body, it tends to deform and tumble, so a larger area of the bullet is presented at the skin as it exits. This causes an irregularly shaped wound at the skin surface (Figure 11.7 A,B, Figure 11.8). However, despite entrance and exit wounds having some individual unique visual characteristics, frequently they cannot be differentiated on visual examination alone. From a medicolegal point of view, the physician should describe the appearance of all wounds, ideally with photo documentation, avoiding any characterization of a wound as entry or exit.
Figure 11.7 A,B Close-up image of entry site of a low-velocity gunshot wound, with erythematous abrasion ring at the edges of the circumferential wound (A). Close-up image of the exit wound (B). Note the larger and irregular edges caused by the tumbling bullet.
Figure 11.8 Multiple low-velocity gunshot wounds to the anterior abdomen. The wounds do not need debridement and they should not be sutured.
Assessment of all missile injuries, irrespective of velocity, includes physical examination and radiologic studies (X-ray, CT scan, CT angiography, or catheter angiography), in order to determine the bullet path, fragmentation, and injuries to the underlying organs, bones, or neurovascular structures. Wound management includes washout, tetanus prophylaxis, and a clean dressing. There is no need for surgical debridement, and the wound should not be sutured because of the high incidence of infection (Figure 11.8).
High-Velocity Projectiles
High-velocity missiles (>1000 ft/sec or 340 m/sec) are mainly used by the military, but they are not uncommon in urban civilian injuries (AK-47 rifle at 1,130 m/sec, M-16 rifle at 1,100 m/sec, 0.347 handgun at 423 m/sec) (Figure 11.9). They cause much more extensive tissue destruction than low-velocity missiles, and the mechanism of injury is more complex. High-velocity bullets travel straight without any tumbling. However, some bullets (AK-47, M-16) flip once (180 degrees) when they hit the tissues and then travel backward (Figure 11.10).
