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What is bullet wounds – in forensic science
admin to Forensic Science  



Contrary to popular belief, it is not always easy to identify bullet wounds, nor is it always easy to distinguish entrance wounds from exit wounds. Once identified (usually by the medical examiner or pathologist at autopsy), information can be gathered from the wounds, including estimates of distance of the shooter from the victim and relative positions of each. High-powered weapons such as rifles can produce massive damage, but injuries from smaller weapons such as pistols and revolvers can leave identifiable and characteristic wound patterns.

When a bullet strikes flesh, the skin is first stretched and then broken as the projectile penetrates. As it enters, material on the surface of the bullet such as dirt and dust, lubricants, powder and primer residue, and lead will be wiped onto the skin in a pattern called bullet wipe or smudge ring. The bullet will also scrape off skin cells, creating an injury called a contusion ring. These features may be obscured or altered by the presence of clothing, and in some cases the bullet-wipe pattern may obscure the contusion ring. The shape of the bullet wipe and contusion ring can provide clues about angles and relative positions; in the case of straight-on shooting, these features will be roughly circular but can be more oval shaped if the shot comes from an angle or is offset from center. Beyond the bullet wipe and contusion ring there will be a dispersed deposit of material (gunshot residue, or GSR) that contains flakes of unburned powder and other residues. The concentration of these residues and how much they are spread out will depend primarily on the distance between the shooter and the victim. In general, the closer the two are, the smaller the dispersal will be. The pattern can be altered by conditions at the scene; for example, if it is an outdoor scene and there is a wind blowing, residues may not reach the skin as they would in an indoor scene or on a calm day.

Once the bullet passes through the skin, its path is not predictable. The bullet may break up and create several paths, or the bullet (or fragments) may strike bone and be further diverted or damaged. Fragmentation can result in several exit wounds. In the case of jacketed bullets or those that stay intact, the exit wound may be characterized by a ragged, exploded appearance, but this is not always seen. Exact trajectories are determined at autopsy, using dissection and X-ray techniques (radiology). At the scene, blood-stain patterns can also be useful. If a weapon is fired at close range, a back spatter of blood may be deposited on the shooter and/or objects nearby. Similarly, a forward spatter can be produced when the bullet or fragments exit the body. There is usually more forward spatter than back spatter, and the different directions of travel can impart distinctive characteristics to the spatter patterns.

The appearance of the entrance wound depends on the distance the gun is from the victim. Contact wounds from pistols and revolvers, particularly to the head, are often distinctive. A muzzle print may be imparted to the skin, and since the barrel is pressed against the skin, gases are forced under the skin and expand and can tear the skin away from bone structures beneath. This tearing results in a characteristic star-shaped pattern in the wound. Close-range shots, considered to be those taken from approximately 12-18 inches typically show the pattern illustrated in the figure. The farther the two are apart, the more dispersed the tattooing pattern will be. Distance shots taken from more than 18 inches (457.2 mm) often leave no visible GSR around the wound, although sensitive chemical and instrumental tests may still reveal the presence of residues.

Wounds from shotguns are different in that the projectiles fired are small circular shot. Distance between the shooter and victim can be estimated based on the dispersal of shot and how much has struck the victim. A close or contact wound produces tremendous damage, but as the distance increases, so does the dispersal of the shot.