"It is not generally recognized that when a high velocity missile strikes the body and moves through soft tissues, pressures develop which are measured in thousands of atmospheres. Actually, three different types of pressure change appear: (1) shock wave pressures or sharp, high pressure pulses, formed when the missile hits the body surface; (2) very high pressure regions immediately in front and to each side of the moving missile; (3) relatively slow, low pressure changes connected with the behavior of the large explosive temporary cavity, formed behind the missile. Such pressure changes appear to be responsible for what is known to hunters as hydraulic shock—a hydraulic transmission of energy which is believed to cause instant death of animals hit by high velocity bullets."
Firearm

January 1, 1970