A DISQUISITION ON THE MECHANISM OF KILLING


Part One: "Hydrostatic Shock" Is Nonsense

Some time ago in a discussion via e-mail I received this comment:

What you describe is what I get using a 165 grain hollow point in my 7 Magnum on deer or a 150-180 grain Core Lokt in the 06. Massive internal, liquefied destruction of chest cavity organs; drop, fold stay right there.  

Now, this comment is based on the writer's acceptance of the fallacy of "hydrostatic shock," i.e., the idea that "...an animal's body is mainly water" (true) and that "...the bullet creates a shock wave that destroys internal organs" (quite false). The appearance of "...internal liquefied destruction of chest cavity organs" is often advanced as "evidence" for this particular bit of misinformation, but it's a misinterpretation of what the hunter is actually seeing. Nothing of the sort happens. Nevertheless the belief in the idea of "hydrostatic shock" stubbornly persists even among people who really ought to know it can't happen. I refer my readers to the work of Dr Martin Fackler, an Army physician and surgeon who knows more about the mechanism by which a bullet kills than most people and has produced an elegant explanation of the process.

The liquid you find in the chest cavity is of course blood, but it wasn't there when the shot was fired.  The bulk of the volume of the chest is air, not liquid.  If there is no liquid no "hydrostatic shock" can occur. Yes, there's a mess when you open up the chest, because the lungs constitute an enormous capillary plexus: when you put a bullet through them, the animal bleeds to death very rapidly

The interior volume of the lungs is filled with air that's physically isolated from the blood circulating through the capillaries. Movement of the blood through the capillaries allows oxygen to cross the barrier of the capillary walls and into the blood; it then flows to to vital organs, most especially the brain. Stop this flow, or deprive the brain of oxygen, and it's lights out.

Put simply, death from exsanguination comes about by depriving the central nervous system (and the rest of the body) of the oxygen supply needed to keep functioning. This will happen even faster if the bullet cuts the aorta or pulmonary artery, or if it hits the heart, because doing so releases even more blood into the chest. But the "soup" is the result of blood entering the chest cavity after the damage is done, often several seconds after. 

In addition to depriving the brain of oxygenation because blood escapes into the chest cavity, the lungs deflate. This is not due the bullet's effect on the lungs per se; it's because they are normally inflated by the air pressure differential between their lumen (which is open to exterior world via the mouth and nose) and the space around them.  This pressure differential keeps them patent and as the chest expands normally, they inflate further; when the chest is compressed, they deflate. This in-and-out is "tidal breathing" typical of all mammals. Punching a hole in the chest wall, however it's done, immediately equilibrates the air pressure in the pleural cavity (the space around the lungs) with the atmospheric pressure in the interior of the lungs. The lungs collapse from their natural elasticity.

A hole in the chest wall can occur in many ways: when it happens it causes a "pneumothorax" a term meaning "air in the thorax," the space around the lungs. If somehow the chest wall could re-seal immediately and the pressure difference restored the lungs won't deflate, or if the seal isn't perfect, they'll deflate only as slowly as the holes in the actual lung tissue would allow. That wouldn't be nearly so rapid as if the chest wall itself is breached. An example: an ice pick stabbed into the chest can create a small opening and lead to a pneumothorax. But that small a hole can be resealed pretty easily. If the ice pick does indeed rupture some lung capillaries, normal clotting mechanisms will seal the breach and eventually breathing will become normal. This is what happened to President Ronald Reagan: a small caliber bullet created a small hole, and a pneumothorax resulted: once he was in the hospital and the hole surgically sealed, he healed and went back to normal in time.

But there isn't and there cannot be any sort of "shock wave" that spreads through the chest, because there isn't anything there to carry it. There is NO free liquid in the chest cavity of a functional, normal animal.  ALL of it is in blood vessels. In short, a bullet kills exactly the same way an arrow does: by removing the pressure differential and cutting numerous capillaries so that the animal bleeds to death rapidly.

The "instant stop" that's often described with a chest hit is dependent on whether or not the bullet also hits a neural structure important to locomotion. It is perfectly possible for a deer shot side-to-side through the chest, even with an exit wound 3" or more across, to run 100 yards or further, provided that the bullet doesn't damage the mechanics of the legs or the neural circuits that control their movement.  That deer is "dead" in a clinical sense, but it takes him a few seconds to get to the point where anoxia in the brain finishes him off; in those seconds he can run a long way, the movement of his muscles adding to the blood pouring into the chest as it is returned to the disrupted lungs.  He drops not because of the hit in the lungs as such, but because he simultaneously is hit in a major nerve tract that controls a lot of things, including his legs.

All of us have seen a deer shot and watched it running, dropping after some distance.  Another deer is shot, seemingly under identical circumstances, but instantly drops in its tracks.  If you did a careful and proper post-mortem exam on those two animals, the way you'd do it on a human who was shot, here's what you would find:

In deer #1 the bullet probably broke a couple of ribs going in and out, and may even have hit a shoulder joint.  But it didn't hit the spinal cord or the brain.  That's why the deer was able to run away at all. You would however find that deer #2 had the bullet, a piece of the bullet, or perhaps a bone fragment, intersect a major nerve tract, most especially the spinal cord. Deer whose wounds consist only of soft-tissue damage simply don't drop in their tracks.  They can't.  They may stand there and look bewildered and fall over, they may get up and run, but the dead-in-its-tracks phenomenon has to involve a hit that compromises the nervous system in some way.

I once shot a deer side to side through the chest with a .30-06 at more or less point blank range. He stopped walking and looked around, then started moving up a hill to my right. Halfway up I could see him wobbling and hear a "swoosh-swoosh" noise as the blood that was pooling in his chest from internal bleeding started to blow out the entry and exit wounds. In about 15 seconds he keeled over dead. This has happened more than once in my hunting life, as no doubt it has to many other hunters.

The next time you eviscerate a chest-hit animal, take the time to clean off the blood and look carefully at what organs are there. I will bet that you'll find that they all are, and that only very small areas of them are damaged.  You probably would also find that the dry weight of the deflated lungs have the same weight as the live inflated ones, allowing for any physical structural damage.  Such an "experiment" would show that actual tissue loss is limited, but that isn't relevant to the lethality of the wound.

I have sort of done this "experiment." The image above left shows the lungs and heart of a deer I shot at about 40 yards using a black powder rifle. In it I've highlighted the bullet track with arrows: it went from the right side to the left side, the bullet exiting (as it always does with a .54 round ball). The bullet track is quite plain, a sort of deep groove across the lungs that of course are deflated but otherwise remained intact. The heart wasn't touched. That deer dropped in his tracks, probably because the hit was high enough to nick or even sever the spine. But the injuries to his lungs are what killed him and account for the massive amount of blood that was present in the chest when I opened him up. No "hydrostatic shock" killed him: blood loss did.

The second image at right is that of the heart-lung area from a big doe shot with a .308 at all of 11 yards. She went a few yards, leaping an obstruction, and piled up stone dead on the other side after moving perhaps 10 yards from the place where she was shot.

The bullet hit her in the left shoulder, expanded as it passed through the shoulder blade, and then went on to turn the heart into hamburger: what's left of it is indicated by the arrow. The bullet exited and was never found. But it's quite obvious that again, the lungs are intact: you can see them in the lower foreground. Both appear to have holes in them, which is what you'd expect given the placement of the heart between the lungs. But there is no "liquification" in any sense. This deer died from massive and almost instantaneous exsanguination. Not "hydrostatic shock."

If "hydrostatic shock" via some sort of "shock wave" being propagated through the liquids of an animal's body were a valid theory to explain how a bullet kills, using a full-metal jacket bullet would be as effective as using soft-points, assuming identical bullet weight and velocity. But as all hunters know, FMJ bullets are far, far more likely to make a small entry and exit wound, and are far less effective as killers than expanding bullets. This is not because the latter create a "shock wave" but because the increased diameter raises the likelihood that the bullet will hit something important like a major blood vessel or a nerve tract.

To sum up, a bullet is more violent than an arrow, but the mechanism by which death occurs is exactly the same.


Part Two: "Energy Dumping" (A/K/A"Energy Transfer") Is Also Nonsense

Having discussed the fallacy of "hydrostatic shock," I'd like to address the nonsense of "energy dumping." This is another concept that intuitively makes sense, but is in fact wholly invalid. It's the idea that if the bullet's kinetic energy is "dumped" into the animal, thereby killing is effected; people who adhere to this belief think a bullet should be retained, and not exit. They're flat wrong.

Let's look at a bullet with a lot of kinetic energy, say that 150 grain .308 that killed the doe described above. At 11 yards, it would have very nearly as much energy as at the muzzle: according to the manufacturer, that would be 2600 Foot-Pounds (FP). Since energy's "equivalent currency" is heat, that can be converted to 3.4 British Thermal Units (BTU).

One BTU is the amount of heat necessary to raise the temperature of one pound of water by one degree Fahrenheit. So the total energy of that bullet at point blank range is enough to raise the temperature of roughly 1.5 quarts of water by one degree.

A 120 pound deer is (approximately) 70% water by weight. That would be 84 pounds of water in all. At 2.09 pounds per quart, that 84 pounds is equivalent to a shade over 40 quarts. To raise that deer's body temperature by even one degree Fahrenheit would require 11.76 BTU's, nearly 3 times what that .308 bullet could "dump" into the body, assuming that a) it does not exit; and b) that all of the energy is retained in the deer.

It should be obvious, then, that "energy dumping" is just as fallacious a concept as "hydrostatic shock." At best the deer's body temperature could be elevated by 1/24 of one degree Fahrenheit. The deer would gain that much energy—more—from its environment just by standing still in the sun for a few minutes.

More arguments against "energy dumping" can be advanced based on common sense. A 3200 pound automobile moving at 45 miles an hour has a total kinetic energy of 217,800 FP, or 280 +/- BTU. If it hits that 120 pound deer and all of its energy were to be retained in the deer's body, that would be 3.3 BTU per pound. In theory it would elevate the body temperature by 24 degrees Fahrenheit, maximum. If "energy dumping" had any validity at all, the animal should evaporate into red mist; but as all of us who have hit deer with a car can attest, that doesn't happen. Ever. Not infrequently the deer gets up and runs away.

Another common-sense argument that deflates the notion of "energy dumping" is the fact that a lot of animals (and humans) are walking around with retained bullets, shrapnel, or whatever embedded in their bodies. Not a few of these are individuals who have been shot with heavy-caliber handguns and didn't die from "energy dumping," or they wouldn't be walking around. The same colleague who gave me the shattered deer humerus (I discuss this below) had in his collection a hippopotamus skull: in it were embedded not one, not two, but three bullets from a .303 rifle. All of the energy of those bullets was "dumped" into the head of that hippo just inches from the brain: yet it lived for years afterwards until it was killed by a shot into the heart. I'm sure he had one hell of a headache for a long time, but he didn't succumb to "energy dumping," he eventually died from massive blood loss.


Part Three: How Many Pellets Are Needed To Kill A Bird Cleanly?

Now...on to the subject of shotgun pellet impacts and rapidity of death in animals and birds.  Please bear with me while I sing my song again.

Shotgun pellets fired into a mammal (e.g., a squirrel or rabbit) kill that mammal the same way rifle bullets do.  A pellet is nothing but a very small bullet, after all. But a pellet has to hit something in the nervous system, preferably in the central nervous system, for an instant kill.

The best example I can think of is a squirrel or a rabbit taking a load of small shot.  If you put 15 pellets in that rabbit's ass with a going-away shot, he is likely to get away.  But if even one pellet hits him hard enough in the head to reach the brain, he is going to die immediately from CNS damage.  There is an oft-repeated mantra about having to "...have a minimum of 3 (or sometimes 5)" pellets to assure a clean kill, this again being based on the fallacy of energy transfer.  The fact is that the minimum to assure a clean kill is one, properly placed; and if every pellet in the load hits the animal, but nothing essential to life is touched, that animal will survive.

Now, birds are much tougher to kill cleanly than are mammals.  You cannot rely on chest hits to kill them outright.  A chest shot mammal is a dead mammal, whether or not you find him:  his odds of survival are very low, almost zero, because if he can't make his lungs work, even if he doesn't bleed out, he'll die of anoxia eventually.

But birds don't ventilate their lungs the way mammals do. They don't have a chest cavity with a pressure differential to keep their lungs inflated. (Anatomically they don't have a chest cavity at all.)  Rather than expandable lungs, birds have a series of "tubes," some carrying blood and some carrying air, lying next to each other; the avian lung is stiff and non-inflatable.

A pellet in the lungs will obviously cause hemorrhage.  But that hit cannot and will not cause the lungs to deflate, because they aren't inflated in the first place.  Birds don't rely on the same mechanism of breathing that mammals do. Instead of a "tidal" cycle, birds ventilate their lungs in a "flow-through" pattern using air sacs in their hollow bones. While a bird may bleed to death from a chest hit, usually he can still circulate both air and blood through the undamaged part of the system, and in most cases he'll have enough remaining tissue that he might just survive, if his bleeding stops. He almost always will have enough circulation through his lungs to get away.

Therefore, there are only two ways to kill a bird: a CNS hit that kills him instantly or one that causes such massive soft-tissue damage that he bleeds out.  (And of course if his wing is broken and he can't fly, if you catch him and wring his neck he's toast.) Birds' innards are so protected by feathers, flight muscles, and bone that getting a pellet into the important parts is tough, much tougher than it is with mammals. This is especially true of big waterfowl: an 11-pound Canada goose has so much "armor" that about the only way to kill one outright is to hit him in the head or the spine. This isn't that easy to do. In the pre-lead ban days Canada geese were hunted with lead shot sizes in the #2 range, but with steel pellets present day hunters have moved up to the larger T and F sizes. They've had to: steel pellets are inferior to lead because the energy levels of a steel pellet are low enough that penetration becomes a real problem at any significant range, especially on large birds. 

All round pellets have lousy form factors and lose velocity rapidly, whether they are lead or something else.  Steel is worse than lead because it's so much lighter, i.e., it loses velocity and energy more rapidly than a lead pellet of the same size. Steel pellets have a double whammy in that not only do they have a very poor ballistic coefficient, steel pellets made have much lower energy levels than lead pellets of the same size with the same ballistic coefficient.  Steel shot loads partially make up for this by boosting velocities, so that paper energies are the same as lead (at the muzzle). The practice of "moving up two shot sizes" partially compensates for the low sectional density of steel pellets so hunters have made the switch to bigger ones.

In theory, if you have a pellet of the same size and shape and of the same density as lead, it will at any given range behave exactly like a lead pellet, with respect to its exterior ballistics. The newer non-toxic pellets on the market that integrate very dense materials like tungsten can increase the pellet weight and density in any given shot size; they're a good way to get around the low sectional density and lousy ballistic coefficient of steel shot, but they're very expensive.  

The object of using a shotgun is to punch at least one hole in a critter that will intersect an important structure.  If lead works better than steel in the same size, it is because of better retained energy due to higher sectional density; that drives the pellet deeper than a steel one of the same size would go.  If a non-steel, non-lead pellet is used, and it has the same sectional density and energy on impact as the lead one does, it will work as well—that is, drive as deep—as the lead one would. 

But there are other considerations. First, lead pellets are soft enough that they often deform when contacting bones, and therefore they "expand." Their chances of making that all-important intersection with a vital structure are somewhat better.  I've seen a lot of deformed lead pellets from small game, so this happens, but any normal sized pellet is so small that even if it's "expanded" the odds of it making a difference in killing effect is minimal.

The non-lead, non-steel pellets are very hard, much harder than lead.  They are less likely to deform and more likely to penetrate, assuming they retain sufficient impact energies.

Sometimes non-steel, non-lead pellets are not, in fact, as dense as lead though they may come close.  The figures I've seen are something like 88% to 92% of the density of a lead pellet of the same.  It would be simple to calculate the energy levels of a pellet and compare lead and non-lead non-steel pellets in this way.  The difference may be more significant than is immediately apparent, and could account for the difference. If someone could design a non-steel, non-lead pellet with the same density and the same malleability as lead pellets, they would work as well as lead.  The only material I can think of that would meet that requirement would be gold.  If you think bismuth shot is expensive, try THAT one.

The flight times and the flight characteristics (trajectory) of non-steel non-lead shot are different from those of "traditional" lead loads. In the early days of the mandatory non-toxic shot requirements for waterfowl, this gave some seasoned hunters problems, because they needed to get accustomed to the differences, adjusting lead and swing. Someone used to lead might find himself shooting a little above, below, behind, or in front of where his intuition tells him he is.  Plus every shotgun barrel is a law unto itself with respect to patterns and performance.  A barrel that patterns well with lead and/or steel may or may not do so with non-steel non-lead.

With respect to upland game and birds, in most places non-toxic isn't mandated (yet) but this is surely coming, given the incessant war on lead being waged by the EPA, other agencies, and some hard-Left non-profit organizations (e.g., the so-called "Center For Biological Diversity," a virulent anti-hunting group thinly disguised an "environmental program"). Since such people have a lot of the characteristics of religious fanatics, they never give up and they never go away. In time upland hunters can expect to be harassed into using non-toxic shot, as waterfowlers have been for decades.

But the fact is that steel shot works very well on small game for a couple of reasons. First, it's very hard and doesn't deform much in passing through a shotgun's choke. Patterns with steel shot tend to be very tight compared to lead shot of the same size fired through the same degree of choke constriction. Squirrel hunters, for example, usually fire at animals that are moving slowly or sitting in a tree: these conditions are very favorable to the use of steel shot. I've killed more than a few squirrels using steel and can attest that it's very, very effective on these small animals.

Second, since most small game animals are just that—small—and don't have the "armor" that birds do, the enhanced penetration of non-deforming steel shot will make it at least as effective as lead.

The false notion that some "minimum" number of pellets is needed for a clean kill on birds or small animals is negated by these facts. A steel pellet of reasonable size will penetrate as deeply as needed to reach vital structures. Someone who uses #6 lead on small game but who moves "up two sizes" to #4's in steel will find essentially no difference in terminal performance.


Conclusion

In the end, bullets and shotgun pellets kill the same way: by causing massive blood loss or by interfering fatally with nerve transmission and control of major organs. If neither of these two things happens and the animal doesn't succumb to infection, he will likely recover. We've all seen deer walking on three legs because one was shot off or broken in a collision. These deer may (or may not) be subject to greater chances of predation, but they may well live a lot longer than we might think.

I offer as proof of this assertion two images. One is that of the humerus (upper arm bone) from a doe whitetail that was found by one of my colleagues in a pile of bones lying in a field. This deer had been shot by some numbskull with a charge of #8 birdshot; one of the pieces of shot is indicated by the arrow.

We don't know how the doe died, but we do know she didn't die from being shot. Her humerus and the joint with the shoulder blade was churned into powder, but she lived: and she lived a long time. The fragments of bone "healed" into a fused mass that actually formed a new articulation with the scapula. That process would have taken at least a year, probably much longer.

The second example is from a fox squirrel I killed some years ago. This animal was behaving perfectly normally until I knocked him out of a tree with my shotgun. On preparing him for dinner I found, embedded in the muscles of his leg, a steel air rifle pellet! Someone had shot him with a BB gun, I think, and the shot broke his leg. But the two ends of the broken bone healed together to form a new, intact leg, albeit one that was about half an inch shorter than the one on the other side. Again, this would have taken a year or more to happen. That squirrel was not externally distinguishable from an uninjured one, nor did the injury affect his ability to climb and jump.

As painful and debilitating as these injuries must have been, in neither case did the hit impact a vital structure. And (certainly in the case of the deer) "energy dumping" must have occurred. But it didn't kill either one of them!


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