Ballistics of Gunshot Wounds

Fig. 1.1
Precession or rotation of the bullet around the center of mass due to spin

Nutation

Small circular motions at the bullet tip (Fig. 1.2).

Fig. 1.2
Nutation, small circular motions at the bullet tip

Energy Transfer in Gunshot Wounds

The Fallacy of Equating Wound Severity with Velocity

A better understanding of gunshot wounds eventually uncovered the direct relationship between the severity of the gunshot injury and the amount of energy transferred by the projectile , which is ultimately related to the velocity and distance travelled. As such, a more pertinent classification regards “high-” versus “low”-energy injuries [2]. For instance, published ballistics data reveals that the muzzle energy drops markedly beyond 45 m for the majority of handgun bullets, and beyond 100 m for rifle bullets [3]. However, most civilian gunshot wounds occur at ranges of 10 m [3].

• High/low energy inaccuracy—importance of energy deposited in tissue

Nevertheless, describing gunshot wounds as high “versus” low energy was a misleading estimate because impact energy (kinetic energy) is not the only factor. In reality, tissue disruption is due to the amount of energy dissipated and transferred from the bullet to the tissues, and quantified as E = 1/2M(V entering 2V exiting 2) [2, 3].

• Energy transfer and tissue resistance—relation to presented surface area

The amount of energy transferred from the bullet to the tissues, which generates the damage, depends on four main variables [6].

• The first factor is the amount of kinetic energy possessed by the bullet at the time of impact, which is a function of its velocity and mass.

• The angle of yaw of a bullet at the time of impact, which is defined as the deviation of the long axis of the bullet from its line of flight, also influences the amount of energy transferred to the tissues. The greater the angle of yaw of a bullet when it strikes the body, the greater is the contact surface area, and hence the greater is the loss of kinetic energy.

• In fact, as the bullet moves further from the muzzle and with its destabilizing gas effects, the maximum amplitude of yaw gradually decreases. This correlates with the observations that close-up wounds are often more destructive than distant wounds because of increased bullet stability with increasing range. In addition, this explanation supports the observation that a rifle bullet penetrates deeper at 100 m than at 3 m [6].

• With tumbling of the bullet, a much larger cross-sectional area of the bullet to be presented to the target is needed. Hence, a shorter projectile will tumble sooner than a larger projectile [6].

• The third factor that governs the amount of kinetic energy lost and transferred to the tissues in the body is the bullet’s characteristics: its configuration, caliber, and construction. Bullets with a blunt nose, which are less streamlined than pointed spitzer bullets, are more retarded by the tissues, and subsequently lose greater amounts of its kinetic energy. By contradistinction to the fully-jacketed bullets, an expanding ammunition disintegrates in the tissues. Consequently, by shattering and mushrooming they are more retarded than fully-jacketed bullets [6].

• Of note, the caliber of a bullet and its shape are important determinants of the initial value of the area of interphase between the bullet and the tissues, and subsequently influence the drag of the bullet. Once the bullet is deformed, the shape and caliber decrease in importance [6].