A penetrating missile transfers energy to the surrounding tissues. Impact imparts a temporary pressure wave perpendicular to the path of the bullet, accelerating tissue forward and sideways. The force generated is such that the tissue particles, because of inertia, continue moving after the missile passes. This expands the tract into a temporary cavity up to 30 times the original cross-sectional area. This quickly collapses on itself.
Superimposed on these pressure waves are shock waves directly related to the velocity of the missile. Tissue elasticity, hemorrhage, and edema are the factors influencing cavity collapse. All structures in the bullet track are destroyed or pushed aside. A smaller permanent pathway marked by vapor bubbles, hemorrhage, bullet fragments, and sometimes bone chips is left behind.
Shotgun wounds differ somewhat from handgun and rifle wounds. As with other firearms, the velocity of pellets as they strike the intended target is the primary determinant of wounding capacity. Additional variables include the pattern of pellets, the number of pellets, the size of the pellets, deflection of the pellets, and the distance of the target from the muzzle blast.
Figure 5, A-C: Intentially, self-inflicted rifle injury, barrel-in-mouth. There are fractures of the anterior maxilla, hard palate, nasal bones, numerous ethmoid septae, bilateral medial orbital walls, and anterior walls of the frontal sinuses. The soft tissue of nose has been avulsed. Due to lack of yaw movement in a rifled bullet, the field of injury is small compared to a shotgun would and is limited to the central face. There are no injuries of the lateral midface, mandible, orbits or lateral cranium. Due to the high velocity, however, the destruction in the path of the bullet is extensive.
Figure 6, A-E: Intentionally self-inflicted shotgun injury, barrel-under-chin. Explosive injury to a large area of the mandible, midface, orbit, and cranium. Innumerable BBs are seen from the jaw to the forehead. Explosive blast effect on the left side with soft tissue lacerations, hemmorrhage, torn vessels, and vapor bubbles. Fractures of the mandible, maxillary sinuses, orbit, frontal sinuses, and calvarium are visualized with significant displacement of bony fragments from blast effect typical of low velocity projectiles.
When projectiles penetrate living tissue, the injury is directly related to the amount of energy transferred to the target. This is expressed by the equation: E = mv2 / 2 where E = energy transferred, m = mass of the missile, v = velocity of the missile. Thus, wounding capacity is most directly related to the energy imparted by the missile's velocity as it violates tissue. Bullets are lead projectiles covered by a copper or brass jacket. Jacketed bullets are more likely to fragment on impact. A fully jacketed round travels further and is more accurate than a "dum-dum", which is designed to deform on impact, increasing its effective diameter. The shape and consistency of a bullet greatly influence the nature of the wound. Hollow, soft type bullets will deform on impact, thus increasing their area of contact with tissue. The release of energy to tissue is enhanced, thus causing more extensive damage. This type of bullet is less likely to exit from the target.
Figure 7, A-C: Intentially self-inflicted handgun injury across the orbits. Projectile path across the front bones with the buellet traveling extra-cranially in the posterior orbits, severing the optic nerves, and causing extensive soft tissue laceration and hemorrhage. Due to shock-wave effect of high energy (high-velocity) projectile, numerous fractures of the bones of the midface, paranasal sinuses, and orbits are identified.
Figure 8, A-C: Intentionally self-inflicted shotgun injury, barrel u nder the chin. There is a large zone of injury involving the mandible, lower, middle, and upper face, including the right orbit. No injury to the cranial va ult is identified. The calvarium and brain are intact. Close-range gun-barrel effect from rapidly expanding gases mutilates the soft tissues and fractures t he facial bones in a large area beyond the visible tract of missiles (bullets) . Fractures and soft tissue injuries are also appreciated on the left. Numerou s bullet fragments are seen over a large area due to the high-energy blast eff ect.