Centerfire Rifle Wounds.

Wounds from centerfire rifles differ from those made by handguns, primarily because of the much higher velocity and kinetic energy of the projectiles. Recall that the kinetic energy (E) of a projectile increases as the mass (M) and especially the velocity (V) increase, according to the formula E = MV². Rifle entrance wounds are typically regular and sharply punched-out if no intermediary target or other destabilizing influence is applied to the bullet. Abrasion rims may be thin to absent, and there may be tiny radial "microtears" at the margin of the wound. Wounds due to 5.56 X 45 mm cartridges will sometimes have a hexagonal abrasion rim (see the image below).

 

  Distant entrance wound due to high-velocity rifle. Note the absence of residues surrounding the wound and the presence of hexagonal abrasion rim.

Because of the high velocity associated with centerfire rifle wounds, bullets often fragment extensively within the body, resulting in a so-called "lead snowstorm" appearance on radiographs. As the muzzle-to-target distance increases, bullet velocity and energy will decrease and so will fragmentation. Although it will usually be less extensive in long-distance wounds, significant bullet break-up is still the rule, unless the bullet is heavily constructed. See the following images.

 

  Radiograph of a high-velocity rifle wound. Note the extensive fragmentation of the projectile.

 

Radiograph of a high-velocity rifle wound showing the typical "lead snowstorm" pattern of bullet disintegration.

When a bullet passes through tissue, it crushes tissue, resulting in a permanent cavity. It also causes a short-lived temporary cavity, the size and shape of which is greatly influenced by the velocity of the bullet. Because this cavity is partially dependent on velocity, it is much more prominent in centerfire rifle wounds than those due to handguns. The deformation of tissue due to this cavity may cause significant stretching and tearing of the skin and soft tissues of the injured area, the severity of which is partially determined by the elasticity and resilience of the injured organs (see the images below). If a bone is struck and fragmented, the tissue damage will be amplified by bone fragments driven peripherally by the bullet.

 

  Entrance wound due to a high-velocity rifle. Due to temporary cavity formation and resultant laceration of skin, the actual site of the entrance is difficult to see (semi-circular partial defect at the left of lower margin of wound).

 

  Exit wound from a high-velocity rifle injury.

Contact rifle wounds show characteristics similar to handgun wounds, although like shotgun wounds or very powerful handgun wounds, they may have explosive effects when applied to the head. Similar to that of long-barreled shotguns, soot and stippling may be less prominent than that seen in short-barreled handguns. Even distant wounds of the head due to high-velocity rifles may be deceptively stellate because of temporary cavitation.

Projectiles commonly perforate (pass through) one area of the body, such as an arm or leg, before striking the head or torso. In such cases, the initial extremity wound causes destabilization of the bullet, often resulting in a large, atypical re-entry wound on the head or torso (see the following image). If the extremity is in contact with or closely approximated to the torso, there may be contusion and/or abrasion of the skin around the exit and re-entrant wounds.

 

  Re-entrant gunshot wound, passing first through the arm and then into the chest. Note the contusion around the exit wound of the arm and the irregular abrasion around the re-entrant wound of the chest. 

 Author

Randall E Frost, MD Chief Medical Examiner, Bexar County Medical Examiner's Office; Clinical Associate Professor, Department of Pathology, University of Texas Health Sciences Center at San Antonio