Hydrostatic shock
[7] In the scientific literature, the first discussion of pressure waves created when a bullet hits a living target is presented by E. Harvey Newton and his research group at Princeton University in 1947:[8] It is 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.
Such pressure changes appear to be responsible for what is known to hunters as hydraulic shock—a hydraulic transmission of energy that is believed to cause instant death of animals hit by high-velocity bullets (Powell (1)).Frank Chamberlin, a World War II trauma surgeon and ballistics researcher, noted remote pressure wave effects.
[10] He avoided the ambiguous use of the term "shock" because it can refer to either a specific kind of pressure wave associated with explosions and supersonic projectiles or to a medical condition in the body.
During World War II he commanded an 8,500-bed hospital center that treated over 67,000 patients during the fourteen months that he operated it.
Martin Fackler, a Vietnam-era trauma surgeon, wound ballistics researcher, a colonel in the U.S. Army and the head of the Wound Ballistics Laboratory for the U.S. Army's Medical Training Center, Letterman Institute, claimed that hydrostatic shock had been disproved and that the assertion that a pressure wave plays a role in injury or incapacitation is a myth.
A lithotriptor uses sonic pressure waves which are stronger than those caused by most handgun bullets,[6] yet it produces no damage to soft tissues whatsoever.
[6] However, Bellamy's published findings the following year[18] estimated that 10% of fractures in the data set might be due to indirect injuries, and one specific case is described in detail (pp. 153–154).
In their analysis of this data published in the Textbook of Military Medicine, Ronald Bellamy and Russ Zajtchuck point out a number of cases which seem to be examples of distant injuries.
[24] Proponents of the concept point to human autopsy results demonstrating brain hemorrhaging from fatal hits to the chest, including cases with handgun bullets.
[25] Thirty-three cases of fatal penetrating chest wounds by a single bullet were selected from a much larger set by excluding all other traumatic factors, including past history.
"[32] This hypothesis is supported by observations of neural effects in the brain from localized blast exposure focused on the lungs in experiments in animals.
[30] A number of papers describe the physics of ballistic pressure waves created when a high-speed projectile enters a viscous medium.
[34] Lee et al. note the importance of the energy transfer: As would be expected, an accurate estimation of the kinetic energy loss by a projectile is always important in determining the ballistic waves.The rigorous calculations of Lee et al. require knowing the drag coefficient and frontal area of the penetrating projectile at every instant of the penetration.
Göransson et al. were the first contemporary researchers to present compelling evidence for remote cerebral effects of extremity bullet impact.
[21][39] These scientists observed apnea, depressed EEG readings, and neural damage in the brain caused by the distant effects of the ballistic pressure wave originating in the thigh.
A high-frequency oscillating pressure wave with large amplitude and short duration was found in the brain after the extremity impact of a high-energy missile..." Wang et al. observed significant damage in both the hypothalamus and hippocampus regions of the brain due to remote effects of the ballistic pressure wave.
[40][41] Roberts et al. present both experimental work and finite element modeling showing that there can be considerable pressure wave magnitudes in the thoracic cavity for handgun projectiles stopped by a Kevlar vest.
Using sensitive biochemical techniques, the work of Wang et al. suggests even lower impact energy thresholds for remote neural injury to the brain.
In analysis of experiments of dogs shot in the thigh they report highly significant (p < 0.01), easily detectable neural effects in the hypothalamus and hippocampus with energy transfer levels close to 550 ft⋅lbf (750 J).
Courtney and Courtney believe that remote neural effects only begin to make significant contributions to rapid incapacitation for ballistic pressure wave levels above 500 psi (3,400 kPa) (corresponds to transferring roughly 300 ft⋅lbf (410 J) in 12 inches (30 cm) of penetration) and become easily observable above 1,000 psi (6,900 kPa) (corresponds to transferring roughly 600 ft⋅lbf (810 J) in 12 inches (0.30 m) of penetration).
[50] In self-defense, military, and law enforcement communities, opinions vary regarding the importance of remote wounding effects in ammunition design and selection.
In his book on hostage rescuers, Leroy Thompson discusses the importance of hydrostatic shock in choosing a specific design of .357 Magnum and 9×19mm Parabellum bullets.
"[52] Jim Carmichael, who served as shooting editor for Outdoor Life magazine for 25 years, believes that hydrostatic shock is important to "a more immediate disabling effect" and is a key difference in the performance of .38 Special and .357 Magnum hollow point bullets.
We do not advocate abandoning long-held aspects of the load testing and selection process, but it seems prudent to consider the pressure wave magnitude along with other factors.A number of law enforcement and military agencies have adopted the 5.7×28mm cartridge.
[59] The FBI recommends that loads intended for self-defense and law enforcement applications meet a minimum penetration requirement of 12 inches (300 mm) in ballistic gelatin and explicitly advises against selecting rounds based on hydrostatic shock effects.
Whereas virtually all of our opinions about knockdown power are based on isolated examples, the data gathered during the culling operation was taken from a number of animals.
[64] The North American Hunting Club suggests big game cartridges that create enough hydrostatic shock to quickly bring animals down.
