Hydrostatic shock

Hydrostatic shock or hydraulic shock is a term which describes the observation that a penetrating projectile can produce remote wounding and incapacitating effects in living targets through a hydraulic effect in their liquid-filled tissues, in addition to local effects in tissue caused by direct impact. Just as force applied by a pump in a hydraulic circuit is transmitted throughout the circuit because of the near incompressibility of the liquid, so the kinetic energy of a bullet can sometimes send a shock wave through the body, transferring physical shock to tissues whose physiologic function may be disrupted by it (especially in the circulatory or nervous systems). (Other kinds of shock, namely circulatory and psychological, may follow, but mechanical shock is the immediate disruptor.) There is scientific evidence that hydrostatic shock can produce remote neural damage and produce incapacitation more quickly than blood loss effects. In arguments about the differences in stopping power between calibers and between cartridge models, proponents of cartridges that are "light and fast" (such as the 9×19mm Parabellum) versus cartridges that are "slow and heavy" (such as the .45 ACP) often refer to this phenomenon.