FIREARM AND PROJECTILE DESIGN

Although there are many variables, the muzzle velocity (speed of the bullet as it leaves the barrel) and the bullet characteristics such as mass and deformability are the most important determinants of the wound that a particular weapon will produce (Table 1). The muzzle velocity is determined by the caliber of the bullet, the capacity of the casing (amount of powder), and gun barrel length. The bullet’s velocity rapidly increases as it travels down the barrel, but gradually slows upon meeting air resistance once it has exited. Handguns generally accept smaller bullets with less powder and have shorter barrels than rifles, and therefore produce projectiles of considerably less velocity (Table 2).

Table 1 Factors Involved in Wound Ballistics

Table 2 Muzzle Velocity by Gun and Bullet Type

The mass of the bullet is determined by its caliber (diameter), length, and the density of its metal components. Because of its heavier mass, and therefore its increased energy per given velocity, lead is the principal element of most bullets. Lead, however, is a relatively soft metal that deforms readily during high-velocity flight. “Jacketed” bullets have a lead body covered with metal alloys that prevent deformation during flight, and therefore help the bullet retain speed and accuracy over a long distance. Conventionally jacketed bullets will deform when they strike dense tissue, but bullets with thicker jackets are intended to retain their shape and therefore penetrate deeply into large game animals such as elephants (Figure 1). Bullets that deform upon striking the body will cause considerably more collateral tissue damage by direct contact, cavitation, and shock waves than nondeformable bullets. Fragmentation of bullets will also occur when the bullet strikes bone and will add to the damage by shredding surrounding tissue (Figure 2).

Figure 1 Full-metal-jacket .308 caliber rifle bullet that has opened upon impact with a game animal (left) compared with same caliber bullet with a thicker jacket that has passed undeformed through the animal (right). Notice the grooves on the base of each bullet caused by the internal rifling of the barrel.

(Bullets courtesy of Gerald Warnock, MD, Portland, OR.)

Figure 2 (A) Close range .30-06 hunting rifle wound to the right forearm. (B) Radiograph of same injury showing extensive bony comminution and bullet fragmentation. (C) Radiograph of same patient’s pelvis demonstrating extensive fragmentation of the bullet. This patient required lower abdominal wall reconstruction.

According to The Hague Declarations of 1899, military rifle bullets “which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core” are banned. This prohibition was designed to reduce the severity of wounds, and therefore the suffering of soldiers on the battlefield, but does not apply to combatants of noncontracting organizations and does not apply to bullets commonly used for hunting. In fact, “full-metal-jacket” (FMJ) bullets are prohibited for game hunting in many jurisdictions. For this reason, hunting rifle wounds may be more severe than those resulting from an equivalent military rifle. The exception to this principle is the assault rifle, which although its bullet is jacketed, causes severe wounds from the bullet’s tendency to tumble in tissue.

HANDGUNS

Handguns are commonly used in urban areas because they are lightweight and can be concealed. Fortunately, handguns cannot produce as highly accelerated and accurate a projectile as rifles. The amount of gunpowder packed into a handgun bullet casing must be limited to avoid barrel damage and permit the shooter to fire the weapon supported only by their arms and hands. Experienced marksmen can master the handgun under controlled circumstances, but both police and criminals probably strike their target less than half the time in the field. Accuracy is dramatically decreased with distance. The majority of handgun wounds, therefore, are generated from 10 yards or less.