WOUNDING MECHANISMS OF GUNSHOTS
 R.A.S HEMAT, MB;BCh, FRCSI, Dip.Urol.UCL.
Basic physics verifies that a projectile’s potential to disrupt tissue is determined by: 1- both its mass and its velocity, and 2- a bullet’s physical characteristics, by becoming unstable and yawing or running sideways, relative to the line of flight. In 1880, the velocity of small-arms projectiles was doubled from 396 m/sec to 731 m/sec.
The first jacketed bullets diameter and mass were only about half those of previous lead bullets. The jacketed bullets’ much higher velocity required a decrease in bullet mass. The jacket bullets did not flatten or deform in human soft tissue but made small, punctate holes, disrupting little tissue, unless struck bone in which case it might become deformed or yaw. The myth that "shock waves" generated by bullet cause tissue damage was laid in 1947. It is more properly called the sonic pressure wave, is simply the sound of the projectile striking the surface of the tissue or tissue simulant. This sound wave travels ahead of the bullet: The speed of the sound in tissue is approximately 1,450 m/sec, considerably faster than the speed at which bullets penetrate tissue. These sonic waves can be produced in water when steel sphere struck at 914 m/sec, produced pressures up to 60 atm but their duration was but a few microseconds. A second pressure wave follows the penetrating projectile, termed "temporary cavity" results when penetrating projectile strikes tissue, which then accelerates rapidly away (like splash) from where the projectile struck.
Therefore temporary cavity pressure waves produce between 200-300 times more capacity to move tissue than the sonic wave. The disruption of tissue accompanied the pressure changes caused by the temporary cavity, not those of the sonic wave. The sonic pressure (shock) waves generated by 24-inch (6-mm) steel spheres shot at 1,200 to 1,500 m/sec into the legs causes damage to various distant parts of the nervous systems.
Lithotripter generates sonic pressure waves without using projectile, or yielding a temporary cavity. Despite the fact that the sonic waves generated by the lithotriptor have 3 times the amplitude of those produced by small-arms projectiles, and as many as 2,000 waves might be used during a single treatment session for the treatment of renal calculi.
The damage caused in the body by a bullet’s temporary cavity can vary greatly, depending on the size of the cavity and its anatomic location. The force of the temporary cavity follow the path of least resistance, separating tissue planes and tearing tissues where they are fixed and cannot be displaced.
In a shot through the abdomen, the temporary cavity forces move a loop of small bowel only about 3.5 cm. This 9 cm diameter cavity is also likely to be absorbed in muscle or lung tissue without damage. In the liver or kidney, it could cause serious damage because of the tissue’s inelasticity. In the cranial cavity a 9-cm temporary cavity will most likely cause instant death as a result of the inability of brain tissue to move aside…etc
Jan, 2006
Note: The information in this article has been excerpted from the following books: urotext-ebook simplifying urology (urotext-Basics volume 1), Principles of modern urology, by Dr. R.A.S HEMAT. Permission is granted to copy and redistribute this document electronically as long as it is unmodified. This article may not be sold in any medium, including electronic, CD-ROM, or database, or published in print, without the explicit, written permission of Dr. R. A. S. Hemat.
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Dr. R.A.S HEMAT declares no conflicts of interest or financial interests in any product or service mentioned in this article, including grants, employment, stock holdings, gifts, or honoraria.
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