Hydrostatic shock
Hydrostatic shock is a theory of
terminal ballistics that wounding effects are created by a shock wave in the tissues of the target. The term is meant to be a combination of
hydrostatics with the (misnomer) effect of hydrodynamic shock. It is frequently used to argue in favor of low mass, high velocity bullets, especially in American
shooting sports magazines.
Hydrodynamic shock refers to a
pressure wave that is created when liquid is suddenly displaced, such as by a
high explosive. Although it is sometimes used by scientists, the term is a misnomer because shock waves do not occur in incompressible fluids. Such pressure waves are known to cause extensive tissue damage to organisms that they pass through, and have been studied for use in meat tenderization and antibacterial applications.
Following the development of high explosives in the
19th century, it was discovered that setting off dynamite in water caused nearby fish to die
en masse. Although highly efficient,
dynamite fishing was found to be extremely destructive to the environment and has been widely banned, although it is still illicitly practiced in some areas.
Proponents of hydrostatic shock argue that because tissue is composed largely of water, an analogous situation can occur in tissue where organs are damaged in the same manner as fish, more by the shock wave than the projectile itself.
The theory of hydrostatic shock has been conclusively disproven. The claim that tissue behaves like water is obviously false. Water is an incompressible fluid, while tissue is a compressible solid. Tissue has memory and will return to its original shape if stretched, and can dissipate energy as it stretches. What's more, even if tissue did behave like water, the speed of sound in water is approximately 1500 m/s, but no commonly used rifle bullet exceeds 1300 m/s.
Tissue does behave similarly enough to water that a sonic pressure wave can be created by a bullet impact, generating pressures in excess of 100 atmospheres. However, a device known as the lithotriptor, commonly used to break up kidney stones, produces sonic pressure waves of approximately 5 times the amplitude of those caused by bullets. Up to 2000 such pressure waves are used in a single treatment session, with no damage to soft tissues whatsoever.
From a study produced by the FBI, "Handgun Wounding Factors and Effectiveness":The reason is that most tissue in the human target is elastic in nature. Muscle, blood vessels, lung, bowels, all are capable of substantial stretching with minimal damage. Studies have shown that the outward velocity of the tissues in which the temporary cavity forms is no more than one tenth of the velocity of the projectile. This is well within the elasticity limits of tissue such as muscle, blood vessels, and lungs, Only inelastic tissue like liver, or the extremely fragile tissues of the brain, would show significant damage due to temporary cavitation.
Further, one study showed that projectiles which strike above the speed of sound in water do not produce any "extra" trauma which could not be explained by the increase in drag as velocity increases.
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More articles on wound ballistics from B & T Ammo Labs
