hydrostatic shock

This term is most commonly used in reference to the injuries caused by gunshots. The human body is made of mostly water in a relatively closed system. When a high velocity projectile strikes a body, it can damage that body beyond the obvious hole it creates, blood loss, organ damage, the possibility for infection, and psychological trauma. The bullet's impact creates an intense shock to the body, sending waves of noncompressible water radiating from the impact point. The shock can burst blood vessels, damage or rupture organs, break bones, and disrupt nerves.

Firearm projectiles that are designed specifically to create hydrostatic shock are generally banned by international convention. The Hague Convention of 1899 banned the use of dum-dum ammunition, which was soft and hollow and mushroomed upon impact. The contemporary hollow-point round has since succeeded the dum-dum round and is in common use in Amercian civilian and police circles, thanks to its hydrostatic shock capabilities.

Interestingly, the military leaders of most nations were quite willing to accept the much less destructive bullets.

why?

Easy: full metal jacket rounds (the opposite of dum-dums or hollow points) typically wound rather than kill. As every military man knows, a wounded soldier is a much greater burden for the enemy than a dead one.

Oddly enough the British, normally bastions of civilized behavior, were against the portion of the Geneva Convention that outlawed these types of ammunition.

Their reasoning?

<quote>
When wounded, a civilized soldier lies down and awaits aid. The savage however presses on with his attack.
</quote>

They were afraid that their frequently outnumbered colonial troops would be put at a disadvantage if they were denied the use of a round that was designed to cause the maximum wounding effect.

No, I'm not making this up.

The prime factor in the degree of hydrostatic shock imparted by a bullet (after, of course, its total momentum) is the degree to which that momentum is transferred to the body, and how quickly. The dum-dum ammunition referred to above, and the hollowpoint ammo that succeeded it, are designed to maximize shock value through maximizing surface area.

When one of these bullets hits the body, it deforms upon impact. Hollowpoints and the softer dum-dums tend to mushroom outward when they hit. This causes the bullet to transfer more energy, since the larger surface area presented by the bullet after impact causes the amount of energy per square unit area to lower. This lower value means that the bullet has a tougher time penetrating (ripping into, tearing, etc.) the body, and instead transfers more momentum to the surrounding mass. This is usually referred to as 'stopping power.'

Higher stopping power leads to higher hydrostatic shock if the bullet deforms fast enough, which slows it more quickly. The shock is more damaging (the wave is higher pressure) the faster the energy is transferred.

One method of transferring more energy for higher stopping power other than the outlawed deforming ammo is to make the bullet fairly long, which induces it to tumble inside the target. The .223 round used in the American M-16 assault rifle does just that. Fully jacketed, the round rarely breaks up unless it hits a solid target like brick, stone, or metal; however, the tumbling action tends to not only transfer enough energy to provide the stopping power of a slightly larger bullet, but also produces fairly nasty 'tearing' wounds, which are even harder to deal with.

Been so long since seeing "hydrostatic shock" discussed as real, I will confess to be taken aback. First and foremost, small arms and their munitions are designed to kill, not maim. One of the reasons full metal jackets remain in play is the fact that a standard is necessary for economy of scale purchasing, and the rounds submitted for consideration ranged from small explosive devices to hollowpoints that clogged so easily as to be rendered FMJ's and nothing else. The capability to fire through barriers is of prime consideration, and that opens yet another can of worms in deciding what type of expanding ammo sould be employed. Pressure wave incapacitation comes from velocity, and velocity alone, and is a science as opposed to hydrostatic mumbo-jumbo. Rifle's employing 5.56 mm or 7.62 mm NATO cartridges have giddyup from 3000-3600 feet per second, and the wounding is incurred...from full metal jackets, mind you...by the speed of the round and not it's paltry weight.

Handguns are a different story, and SHOULD expand to provide the maximum level of incapacitation. Disregarding central nervous system hits, most targets are not killed in the snap of a finger as seen in theatrical presentations, and even the best of munitions can merely wound. The handgun round relies upon size and placement to perform the task, and since modern armies must now also provide weapon systems for those small of stature, recoil is of prime consideration.

Most NATO countries cheat anyway when manufacturing FMJ's. as there is no super-dee-duper inspector general prancing about to assure that the jacket meets minimal standards, and the French in particular create rounds that are almost painted with copper and not truly jacketed. (Saves lots of money)

The debate has been raging for well over a hundred years, and to keep it simple law enforcement and miltary experts advise the following:

Any bullet over 2500 FPS can introduce an unsurvivable wound regardless of it's design due to the effects of pressure waves upon the target. Any bullet of a lower velocity should mushroom to create a larger wound channel.