The Fascinating Topic of Hydrostatic Shock

Hydrostatic shock – what is it, what does it do, and how much does it matter? Though the concept has been around at least since WWII, there’s a great deal of misinformation about it, and the topic is widely misunderstood even by people who are otherwise knowledgeable about terminal ballistics and the physiological effects of a high velocity projectile. It is the purpose of this article to discuss this topic objectively and in plain English. I wouldn’t dream of calling this “the final word,” but perhaps it can at least give focus to future arguments.

This article also is going to confine its attention to the implications of big game hunting, though most of the arguments presented here will apply to self-defense shooting and small game hunting as well.

How does the hunter harvest his animal?

Before we dive into this, though, let’s quickly review what we try to accomplish when we shoot an animal in a hunting scenario. In a nutshell, we want to:

  • Kill it. This is obviously true, but it’s not a complete answer. As an extreme example, shooting an animal with a dart containing a slow-acting toxin would almost certainly kill it, but perhaps not for days or weeks. Meanwhile the animal runs away, never to be seen again. This is obviously not what we want (to say nothing of the effects of the toxin on the meat). Therefore, we also want to…
  • Incapacitate it very quickly. In short, we want to stop the animal. The ideal hunting shot will stop the prey where it stands. If we can’t do that, though (and we all too often can’t), we want to incapacitate him quickly enough that we can find him. But this also means that we want to…
  • Incapacitate it for an arbitrarily long period of time. It well may not enough to stop the animal for only a few seconds. If the shot animal quickly recovers from its momentary incapacitation, it may escape before we can do whatever proves necessary to “finish it off.”

How does killing/incapacitation happen?

Now that we know what we want to do, we must consider how we go about doing it. Wikipedia defines death as “the termination of the biological functions that define a living organism.”1

For our purposes, though, we need to be more specific: we need to stop our target’s brain activity. When the brain stops, so will the rest of the animal. In the hunting context, stopping brain activity can be accomplished by two methods:

  • A direct hit to the animal’s brain or central nervous system (CNS) will probably immediately cease brain functioning. If you personally feel confident that you can successfully hit your target’s skull (with sufficient force to enter the brain), you can quit reading here and simply hunt with head shots. Most of us, though, are simply not expert enough at shooting to reliably do this in a hunting situation (meaning a quick shot from a less-accurate shooting position like standing or sitting). We prefer then, to stop the animal’s brain activity by another means, namely…
  • A damaging hit to the animal’s vital organs. Apart from a head shot, a shot to the animal’s heart, lungs and/or liver is the quickest and most reliable to kill or incapacitate a target. It is important to realize why this is so. Vital organs represent a heavy concentration of significant blood vessels. As a projectile penetrates these organs, it creates a “wound channel” that damages these blood vessels to the extent that the animal’s blood pressure (BP) rapidly drops. When BP drops sufficiently, blood supply to the brain ceases or slows, and the brain ceases to function. This is not immediate, but assuming that you chose your cartridge and bullet carefully, the damage usually will stop the animal’s brain function in 5 to 10 seconds.

In short, dying comes from the termination of brain function, which in turn comes from a direct hit to the brain (or CNS), or sufficient blood loss to prevent blood from reaching the brain.

The alert reader by now will have noted that there is a third method of incapacitating an animal, namely disabling one or more of its limbs so that the animal can no longer run. While I agree with this method probably would be effective, such a shot must hit and destroy bone; a shot that hits only soft tissue in a limb is unlikely to fully disable the animal. I would venture that hitting an animal’s leg bone is probably at least as difficult as a head shot. It also will not kill the animal, and many animals have been known to move quite capably on only three limbs. I hope we can remove this option from the discussion of desired incapacitation methods without further discussion.

The notion of hydrostatic shock

It has been noted that the term itself is an oxymoron, as the words “static” and “shock” are inconsistent.2 Perhaps a more accurate term would be “hydraulic shock,” but the much more common term of “hydrostatic shock” will be used here.

Many definitions of hydrostatic shock have been proposed, but the general principle is that as a projectile passes through tissue, it creates an energy impulse against the tissue that it contacts. The thinking goes that this energy impulse, and the temporary tissue displacement that it causes (known as a “temporary wound cavity”), can inflict significant damage to the proximate and remote tissue in the animal. Another claim from proponents of the concept is that the energy impulse causes a spike in BP via momentary compression of blood vessels, and that this sudden rise in BP is sufficient to cause remote capillaries in the brain to burst.

But, is any of this true?

Certainly, the temporary wound cavity occurs, if only momentarily. Research using translucent ballistic gelatin and very high speed photography has demonstrated this beyond any doubt. It has also been demonstrated that a faster-moving projectile will generally produce a cavity that is both longer and wider.

But it is widely agreed that living tissue is considerably stronger than ballistic gelatin, and will not cavitate to nearly the same degree. Living tissue also possesses shape-memory and will return to its original shape after a momentary stretching. For these and other reasons, the incapacitating effects of this cavity remain very much in doubt.

The various claims regarding the effects of hydrostatic shock seem to share a premise that living tissue shares physical properties of water. While it’s true that living tissue is mostly water, it is not true that living tissue behaves like water. Water is a fluid; it is not compressible. Living tissue is by contrast compressible.

Proponents of the concept of hydrostatic shock will liken the energy transfer to blood vessels, to an automobile’s hydraulic braking system. This argument, however, is profoundly flawed as it ignores the tremendous elasticity in an animal’s vascular system (indeed, in much living tissue in general). The energy from the temporary cavity is not simply passed along through the blood vessels, as it is when you step on a brake pedal, but dissipated within the living tissue as it moves away from the projectile and then back to its original position.

In fact, there’s no evidence that even proximate tissue is affected in this way. In fact, evidence exists to the contrary. Consider what you see when you dress a harvested game animal. Is the extremely vascular tissue immediately surrounding the wound channel highly bloodshot? Typically not; in fact it’s usually quite intact. If this wound cavity doesn’t rupture blood vessels adjacent to the wound cavity, then how then are we supposed to imagine it can occur in the brain which is probably 24” or more away from a vital organs hit?

There is no doubt that under exceptional circumstances, hydrostatic shock can be devastating. In the highly publicized case of the 1986 FBI shootout with two bank robbers in Florida, an agent was struck in the neck. While the shot missed both the spine and the carotid artery, the agent was paralyzed for several hours. This was attributed to trauma to the spinal cord caused by hydrostatic shock.3 Again, though, it must be noted that these instances are both highly uncommon, and highly unreliable. There is absolutely no guarantee that a seemingly identical shot to another person would produce similar results.

It must also be noted that many arguments in favor of hydrostatic shock (or against the arguments of its detractors) are simply intellectually dishonest. Dr. Martin Fackler, a Vietnam-era trauma surgeon and wound ballistics researcher, once observed that a lithotripter (a medical device used to crush kidney stones with sonic pressure waves) produces no damage to soft tissues, despite the fact that a lithotripter produces far more energy than a typical handgun bullet.4 In an attempt to discredit Dr. Fackler’s argument, one writer cited three studies that demonstrated tissue damage resulting from lithotripter usage.5 What he didn’t say was that such damage was far from immediate, and completely irrelevant to any discussion of terminal ballistics.

Specious arguments like this are sadly common in the world today. It is as though people wish to believe the claims of hydrostatic shock’s stopping power, and don’t mind engaging in a bit of fuzzy thinking in order to substantiate their beliefs.
There is also a lot of anecdotal evidence that individuals allow to get in the way of scientific method. This is understandable but unfortunate. One common example often cited by hunters is that of an animal being knocked down, or even thrown back, when hit by an ultra-fast bullet. While this may occur, it can be attributed to the psychological reaction of the animal, and not to the physical energy exchange. Doubt me? The next time you take an animal in hunting, prop it back up somehow and shoot it again. The utter lack of physical reaction from the dead animal should be enough to convince you.

So, does hydrostatic shock exist?

It all depends on your personal definition of “hydrostatic shock.” Does an animal experience a shock wave when hit by a bullet? You bet. Does this shock wave produce a temporary wound cavity? Again, absolutely.
If, however, you want to claim that these effects cause significant damage to remote (or even proximate) parts of the body, well then, you’re going to get an argument from me. As shown above, in extreme cases, some localized damage may occur, but this is a rare occurrence, and it’s certainly not something to count on.
The bottom line is, while the effects of hydrostatic shock won’t hurt your hunting effort, they’re probably not going to help it much, either. The time-honored axiom that proper cartridge and bullet selection, and accurate shot placement, are what really counts, remains as true today as it was 100 years ago when hunting was done with large, slow bullets that produced little or no hydrostatic shock.

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6 thoughts on “The Fascinating Topic of Hydrostatic Shock”

  1. The author fails to mention numerous published studies supporting the remote wounding effects known as hydrostatic shock. Frank Chamberlain, a WWII trauma surgeon and ballistics researcher, concluded that hydraulic reactions of body fluids and their reactions of the central nervous system were important. In the Textbook of Military Medicine, RF Bellamy documents a number of cases of remote wounding in Vietnam data. Brad Sturtevant, a shock wave expert at CalTech documented a case of remote CNS injury in the spine due to shock wave effects of a 9mm. Scientists with the Swedish Defense Forces have published measurements of the pressure wave reaching the brain and histological findings of remote brain injuries in pigs shot in the thigh. Chinese scientists at the Third Military Medical University have published biochemical evidence of remote brain injury in dogs shot in the thigh in the Journal of Trauma. A Czech researcher has documented microscopic hemorrhaging in the brain in human autopsies of victims shot in the chest in 33 of 33 cases he studied (many with handgun bullets). Outdoor writer Jim Carmichael has described a study by veterinarians showing brain hemorrhaging in Cape Buffalo in cases where the target dropped immediately at the shot. A group at West Point has found that quantitative measures of incapacitation are well-correlated with the magnitude of the ballistic pressure wave in analysis of both animal studies and epidemiological type data of human studies.

  2. Swede –

    There is indeed support for the theory of hydrostatic shock, as an observable phenomenon. There is equally strenuous criticism of conclusions drawn about its effects in the field.

    As mentioned in the article, much of the supporting material is probably better described as “anecdotal” rather than “scientific.” At best, hydrostatic shock is not something a hunter should expect nor depend upon.

    Thanks for the comment.

  3. Fascinating discussion. I think it would be better to assume that hydrostatic shock as stopping power would be a nice side effect (if it happens), and still aim for vital areas. Shooting an animal in the thigh, and expecting it to drop would not be a practical form of hunting in my opinion.

  4. LJ: you’re 100% correct. There is no substitute for shot placement. And if a gun and cartridge are powerful enough to penetrate to the vitals, there’s really nothing more that needs to be said. The notion of hydrostatic shock probably helped sell a lot of magnum rifles over the past few years, but…I’m not convinced it ever killed anything that wasn’t going to die anyway.

    Thanks for contributing; I hope you return to ScopedIn often.

  5. I think this article mixes up hunting and hydroshock (HS) topics a bit. Of course hunters should not rely on some indirect ways to kill their prey. However it doesn’t mean there is no such thing as HS.

    There are two simple things we can take from physics: if there is an foreign body (a bullet) in a tissue, there will be an area of compression around it. If there is a blood vessel, it will be compressed too. A property of liquid that it will redistribute this applied pressure over its volume. In case of fast traveling bullet it doesn’t really matter how soft or elastic blood vessels are, some of the pressure may reach brain or other organs. There is another more extreme example – cases of full bladder ruptures in case of gunshot wounds. It has similiar nature of indirect damage caused by pressure transfered through fluid.

    Can it be fatal is another question. I think in most cases it won’t. But people who reported and investigated it first were doctors and were concerned about mid and long term effects of HS on humans. It’s definetly not what hunter think about when he shoots a deer.

  6. Indeed, a fascinating topic and the input of various writers makes it so. I would like to comment on the “psychological” aspect of a mammal falling down after being shot in what may be a non-lethal area of the body.

    Living in Africa, one sort of gets familiar with the sight of people who have been shot by 7.62×51 calibre standard military back in the day when I was young. Often the people shot would look as if they have been lifted off their feet by the projective. Their shirts would often be out of their pants and up near their chests. Even their shoes would sometimes come off. Not boots – bearing in mind that a lot of them fought in civilian clothing so that they could “bombshell” during a contact, that is, throw their weapons down and scatter.

    As one officer told me, his observation of hits by a 7.62 was like being hit by a baseball bat and magnified ten times. Of course, many hits were multiple and not from a single shot.

    I realize that what I have written is merely anecdotal and not the result of a formal scientific study, merely a reflection of what I have seen.

    Thank you for a very precise and well-written article. It seems to be an ongoing debate but a necessary one.


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