Seems like the best place to start is at the beginning.
Why does an animal die? The answer about God deciding it’s time is perfectly
acceptable to me, but I can’t claim to be able to help anyone understand
more about that angle. Simply speaking, something dies when its computer
(brain) goes down for good. Circulation (blood flow) supports the computer,
which is why we generally use the pulse, or lack of one, to determine life and
death. Generally, one can survive only a few minutes without circulation to
the brain. Nearly anyone can feel a pulse, and while I’ve talked to people
who claim to be able to feel brain waves, I can neither confirm nor deny this
claim. The best indicator of death is the persistent lack of pulse--but it
isn’t foolproof.
Not too many hunters check for the death of their prey
by feeling for a pulse, I’d be willing to bet. Could get dicey with a big
carnivore, or even a little antlered critter. This being the case, we rely on
much less certain indicators, such as "it ain’t movin’" to
determine the success of our kill. That brings me to the next question, and
that is the difference between stopping and killing.
The Taylor Knock-Out Theory
John Taylor’s book African Rifles and Cartridges
talked about the famous "Taylor K.O." method of determining
effectiveness of a bullet against game. Of the K.O. values, he says:
They permit of an immediate
comparison being made between any two rifles from the point of view of the actual punch delivered by the bullet on heavy
massive-boned animals which are almost invariably shot at close quarters, and enable a
sportsman to see at a glance whether or not any particular rifle is likely to
prove a safe weapon for the job. In the case of soft-skinned non-dangerous game,
such as is generally shot at medium and long ranges, theoretical mathematical
energy may possibly prove a more reliable guide, provided a suitable weight of bullet
is chosen for the weight of animal against which it is to be used.
Further on in the same chapter, Taylor described more
about the utility of the K.O. values, comparing the .416 Rigby to the .470
Nitro. He stated that the .416 would probably not knock an elephant
unconscious if a frontal head shot missed the brain, while a .470 would. In
the next chapter Taylor further explained:
...suppose a hunter...has followed
two or three good tuskers into a dense, matted tangle of brush. He can only see bits of one of the elephant, but can hear all
three of them. No vital spot is showing into which he can slip a bullet....if our
hunter has a .577 or .600 along with him, he can take it over now and, because of the
tremendous blow it delivers, can slam a heavy bullet from it into the
tusker’s head with the certainty that it will stun him for an adequate length of time to
enable him to tear his way thru the tangle of brush intervening and still be in
plenty of time to give the elephant another shot to finish him before he
has recovered consciousness. (emphasis added)
My reading of Taylor’s book suggests that, while the
K.O. scale can generalize somewhat to killing power overall, the most
important use he made of the scale was in a very specialized type of hunting,
that of head-shooting elephant.
Now, before some of you start waxing apoplectic, let me
reassure you that I’m not going to make much of that last point, and
besides, I really like the K.O. scale What’s of interest to me here is the
difference between killing power and stopping power. What happened to
Taylor’s elephants that were knocked out was that they suffered what we call
in humans a "concussion". In crude terms, the energy delivered to
the brain, either directly or indirectly, short circuits the portion of the
brain responsible for keeping the lights on, the reticular activating system.
Sooner or later, the lights come back on, and the elephant wakes up and clears
out, often minus its tail.
A similar thing can happen in the case of a spine shot:
nothing about the spinal cord itself is so crucial to either man or
beast that damage to this organ should result in instant death. On the other
hand, when an animal goes out right away with such a hit, the reason could be
found in the shock-absorbing cerebral spinal fluid (CSF) bathing the spinal
cord and brain. An impact to this fluid system could certainly result in the
same concussion to the brain, transmitted indirectly through the CSF.
What Is Happening?
In the mean time, in answer to the questions I can
already hear some of you asking, while the animal is lights out (unconscious),
other things could be happening, and usually are. One of the most important of
these, from the standpoint of survival, is loss of blood from the blood
vessels into the surrounding tissues. This could result in:
1) bleeding into the chest cavity, making
use of the lungs mechanically impossible: no oxygen to the lungs = no oxygen in the blood = no oxygen to the brain =
dead;
2) loss of a critical volume of blood in
any part of the body, producing shut down of the
pump system: lose enough blood (in humans, about 60%), and there’s no way to
keep the pump going: no blood to the brain = dead.
Other usual suspects on the list of
"cause of death" include:
3) sufficient damage to the pump (heart)
itself, which roughly equals 2), since the heart
is the biggest blood vessel;
4) critical nerve damage in the neck,
which could paralyze the diaphragm and make
breathing impossible: no oxygen to the lungs = etc.; and, the most
controversial,
5) "shock", which in humans is
the malfunction or overriding of that part of the nervous
system responsible for keeping blood pressure high enough to assure adequate circulation to the brain and other vital organs.
I can’t give you an authoritative opinion about how
much, or even whether, shock actually occurs in animals. But do I feel that
I’m on solid ground saying that, with a few exceptions, it happens much less
frequently in animals than in humans. (Birds may be different.) I suspect that
if African game really is tougher to kill than North American game, the shock
factor may be the key to understanding why. If the severity of competition in
an environment is high, then the level of alertness must be higher, in order
to keep from either starving or being eaten. This alertness is maintained
through high levels of adrenaline-like chemicals circulating and secreted in
the body of such an animal. The same chemicals maintain blood pressure
(roughly). An animal with a lot of these chemicals is less likely to suffer a
sudden drop in blood pressure, but also will have a higher heart rate, in
general. Its blood pressure is less likely to drop suddenly, but when shot, it
may bleed out faster, as the heart is going faster. More about this below.
Velocity
Finally, and probably most controversially, I think
that the effect of velocity on killing power may be due to effects on
bleeding. I made reference in the first part of this to a comment sometimes
attributed to Elmer Kieth: "ya could eat the bullet hole". This has
to do with the amount of collateral tissue damage, whether from high
pressure/velocity creating what’s referred to as the "temporary wound
channel", or the bullet striking something (usually bone) that shatters
and the fragments become secondary projectiles. All other things being equal,
slower bullets cause less collateral damage than faster ones, of course.
Bleeding is caused by damage to blood vessels, traumatic
or otherwise. Bleeding stops, if it stops, due to constriction of blood
vessels and blood clotting. Constriction of undamaged vessels around the area
of trauma is regulated by those same adrenaline-like chemicals. Blood clotting
is stimulated by chemicals dumped into the blood when the vessels are damaged.
In health, these chemicals reside in the walls of the blood vessels, ready to
go to work if the walls tear. Sort of paradoxically, the more of the vessel
substance that is damaged, the more of these chemicals are made available to
start the clotting process.
On the other hand, in the case of a large caliber bullet
traveling at low to medium velocity, the effect is the opposite. A large hole
is the result, but with less collateral damage. This means, in theory, a big
hole in the vessels (all the way through), with the least non-penetrating
damage to surrounding vessels. Therefore, biggest hole with relatively few
clotting chemicals dumped into the wound.
Disclaimer
That’s my explanation of how animals die. I don’t
see myself as anything more than well-educated, curious, and fanatically
interested in guns and hunting. I know of at least half a dozen readers of
this site who are much more than capable of helping me extract my head out of
the other end of my anatomy, if they see that as the problem. And by the way,
if you’ve made it this far, you either have exceptional stamina, terminal
boredom, or both.
The Entry
The bullet, after traveling from the gun to the animal,
now goes from air to the animal, a medium of different density--usually several
different densities. Many things can happen at this crucial juncture. With
respect to the bullet, it can enter or not. It can fly straight or be deflected.
It can be deformed (expand, break up, or bend) or remain intact. Each of these
changes can have very important effects on the bullet’s killing power.
Obviously, if a bullet doesn’t enter, the effect it has
on the animal has to do with concussion, much the same as throwing a rock. In
general, if a bullet doesn’t enter the animal, it can’t be effective. Now I
know there are exceptions, but realistically, these are stories that are
interesting only because they’re so unusual. The conclusion to draw,
therefore, is that the bullet must have sufficient force and structural
integrity to penetrate that portion of the animal presented.
Deflection can occur at any point, but generally
Newton’s first law of motion applies:
Every body continues in its state of rest, or of
uniform motion in a straight line,unless it is compelled to change that
state by forces impressed on it.
Obviously, any bullet striking an animal already has two
major forces changing its uniform motion before impact. Gravity wants to pull it
to Earth. The friction of the air wants to slow the bullet down. The bullet is
therefore progressively slowing and dropping. But the major velocity- and
direction-changing event happens when the bullet hits the animal. The much
higher density of flesh will always slow the bullet: the only question is, how
much. If the bullet slows enough, it may cause only surface penetration and
damage. Often the bigger effect is the change of direction caused by the surface
tissue. While the bullet may have been aimed directly at an underlying vital
area from outside, when it strikes surface tissue it may angle away and miss the
mark entirely.
The classic example of this is the boss of a cape buffalo
horn. Bone in general, however, is a special case in terms of bullet
performance. Bone and horn are the hardest and most bullet-resistant substances
in an animal’s body, and, inch-for-inch, will challenge a bullet’s
structural integrity more than anything else in an animal’s body.
Bullet deformation can be beneficial or detrimental.
Expansion of the frontal area increases the diameter of both the permanent and
temporary wound channels. Other things remaining equal, this results in greater
tissue damage. However, this change in the shape of the bullet happens at the
expense of energy (which causes the expansion). Remember that this bullet energy
comes from the mass of the bullet and its velocity. Bullet deformation, without
loss of significant weight, must therefore result in lower velocity. Also, an
expanded bullet requires more energy to drive it forward, as the larger frontal
area displaces more tissue as it advances, encountering greater frictional
resistance. Instead, ever less energy is available, so the bullet slows even
more. Eventually, the bullet stops. If it has reached and damaged enough tissue,
the bullet has done its job. If not, it has failed.
Bullet expansion can turn into bullet disintegration,
meaning that the bullet’s structural integrity is insufficient to hold the
bullet together under the energy the bullet develops at that velocity. This
happens with varmint bullets, and also with light and lightly-constructed
bullets in super-zapper magnums. The bullet can separate
from its jacket or shatter all together. Bullet breakup usually decreases
penetration and frequently changes the direction the projectiles take through
the animal, because of loss of both momentum and directional stability.
(This, by the way, is the exception to the rule that Linebaugh sites, that the
weight of the bullet is a constant. His statement is generally true of a
well-constructed solid, and anyone who has read Linebaugh knows that this is
basically his assumption; my observation is not criticism of his position.)
Bullet deformation also includes bending and changing the
shape of the leading edge. Both of these effects generally will result in
deflection of the bullet, and may mean bullet failure. Peter Capstick told some
hair-raising stories about solids in his .375 H&H deforming, turning a
boring day into a lively one, in short order.
The Mid game
From the standpoint of survival, it doesn’t take a
rocket scientist to figure out why vital organs don’t reside on the surface of
animals. The purpose of surface tissue, from plants to humans, is to keep the
inside in and the outside out. The surface also contains openings to the inside
and outside: sensations, air, food, and water come in, and waste goes out. While
no one could reasonably argue that these functions aren’t vital, destruction
of surface tissues isn’t usually lethal. It follows that it takes more than
just getting a bullet into the animal to kill it. As Capstick observed, you have
to do more than just hit meat and arrange for taxidermy. So, what’s inside
that critter you just shot?
Nerve tissue is delicate and easy to destroy. Much of it
is vital to functioning of the animal, especially the brain. Damage to the spinal cord
will instantly incapacitate at least part of the animal, but will not kill the
animal outright.
Puncture blood vessels and they bleed; bigger vessels and
the heart bleed the most. "Vital organs", such as the liver, kidneys,
and lungs, bleed when they are damaged, and so will the other internal organs.
Other tissues bleed as well, of course, but bone, muscle, and connective tissue
are relatively less vascular. In addition, the contraction of muscle can (at
least temporarily) slow or stop the flow of blood. Regardless of the source,
unchecked loss of blood will eventually kill the animal.
Some experts talk about "breaking down the
animal", and there’s certainly a lot to this. It involves damage to the
structures that allow the animal to move, keeping it from running away. In some
animals, damage to the hip or shoulder joints may limit mobility. Much more
certain is the damage to the spine and spinal cord, which immobilizes the animal
by massive nerve damage. J. D. Jones talks quite a bit about shots to the pelvis
or the "spine-tail shot". Done right, this shot damages both bones and
joints, as well as the big bundles of nerves and blood vessels. However, this
shot won’t usually kill the animal; it simply allows the hunter to approach
the animal for a killing shot.
"Shock" is controversial, and must sometimes
enter the picture, but how is a very complex issue, and one that may take
another chapter by itself.
The Function of the Bullet
The bullet must destroy vital structures. I don’t like
to roll the dice, and don’t do so intentionally. Therefore, I define bullet
effectiveness as undeviating penetration, and sufficient
destruction of vital tissue. Let’s take up each one of these in turn.
The bullet may start its flight in the direction of a
vital structure, but if it deviates, it won’t strike its target. If it
doesn’t penetrate sufficiently, it won’t strike its target. Therefore, the
two most important attributes of a bullet in this context are momentum
and directional stability.
Momentum (or, more properly, linear momentum) has a simple
definition from physics:
p = mv
Basically, it is the tendency for the bullet to continue
forward, to go straight and to penetrate. You’ll notice it is also part of the
Taylor KO formula. It’s easy to see that, at the same velocity, a heavier
projectile will tend to carry forward better than a lighter one.
The other motion of the bullet is its rotation, which
imparts a gyroscopic stability to the projectile. The bullet spins from its
having engaged the rifling, and (ideally) keeps its directional stability as a
result.
In addition, this rotation of the bullet creates what is
referred to as angular momentum, which classical physics defines as:
L = Iw
Roughly translated, the tendency of the bullet to continue
spinning is equal to the weight of the bullet times the speed of the spin.
Now here’s where I really got stumped in understanding
the Taylor formula. I could understand how momentum got there, as the product of
bullet weight and velocity. And I thought that the diameter of the bullet in the
equation represented only the size of the hole. But it has also to do with
angular momentum. If the twist of a barrel stays constant, the rotational speed
of a bigger caliber bullet will be greater than that of a smaller caliber
bullet. If the twist is once in ten inches (for the sake of argument), then ten
inches down the trajectory a .45 caliber bullet will have twisted a distance of
.45" x 3.14159..., and a .357 caliber bullet will have twisted and distance
of .357" x 3.14159.... In other words, all other things being equal, a
larger caliber bullet will have a greater speed of spin than a smaller caliber
bullet, and therefore will have greater tendency to keep spinning, even with the
same bullet weight. Of course, the larger caliber projectiles are also usually
heavier, and that tips the balance even further toward the larger caliber
bullet. So the bigger caliber slug will have greater tendency to keep spinning,
and will tend to retain its gyroscopic stability mores than its smaller caliber
counterpart.
The second component of bullet effectiveness is sufficient
destruction of vital tissue. Here, too, the larger diameter slug holds the edge.
Veral Smith of Lead Bullets Technology has pointed out that the size of the
meplat that encounters the tissue of the leading surface is the relevant
variable in determining both the permanent and temporary wound channel. In
general, the caliber of the bullet will determine the hole in the tissue. But
the destruction of the tissue by the forces of concussion and cavitation in the
temporary wound channel has to do with the aerodynamics of the bullet. All other
things being equal, though, a bigger diameter bullet makes a bigger hole, and
destroys more tissue.
Then we get to something that I don’t think Taylor
included in his consideration of bullet effectiveness, and certainly didn’t
include in his formula. I am speaking of sectional density. If a given portion
of the bullet has mass behind it, it will tend to carry forward. In general, the
frontal surface of an intact solid has the full mass of the bullet behind it.
This is not the case with an expanded rifle bullet: the major mass may be
contained in the forward surface, which may have mushroomed as much as 50% of
the bullet weight. The retained weight of the shank of the bullet is behind only
a small percentage of the frontal surface, that in the center. This center
portion of the bullet has some retained sectional density, while the rest of the
mushroomed frontal surface has the sectional density of a lead potato chip. The
tendency of such a projectile to carry must be seriously limited.
So, in summary, a heavier bullet will have a greater
tendency to carry forward and penetrate without being deflected from its course
than a lighter bullet. The heavier bullet with larger diameter will tend to
maintain its rotation, and therefore its directional stability, better than one
of smaller diameter. And finally, the larger diameter slug displaces
proportionally more tissue. The conclusion from this is that the larger heavier
slug should be a more effective bullet.
Force vs. Energy
The usual measure of the power of a bullet is kinetic
energy. Recall the energy is equal to the mass of the bullet, times the square
of the velocity:
E = mv 2
This means, obviously, that the velocity plays a much
greater role in energy than in momentum. So, when the bullet slows down, the
effect of this deceleration is much more profound on energy than momentum. If
the bullet’s velocity slows by half, so does the momentum. The energy drops by
75%!
p 1 = mv (momentum before deceleration)
p 2 = m x 1/2v
(momentum after deceleration)
E 1 = m x v x
v (energy before deceleration )
E 2 = m x 1/2v
x 1/2v, or
E 2 = ¼ mv 2 (energy after
deceleration)
My conclusion from this is that energy dissipates much
more quickly than momentum, meaning that those wonderful huge energy numbers go
away very quickly. As I pointed out earlier, there are a couple of things that
conspire to decelerate the bullet. One of these is the friction of the tissue on
the bullet. Another is the energy needed to deform the bullet. The third is the
increased friction on the leading surface of a bullet which has expanded. The
conclusion is-- correctly--that an expanding bullet retains less energy in
expanding, and loses energy more quickly after expansion.
I know that the rejoinder is that the energy is
transferred to the animal, somehow imparting death to the quarry. It ain’t
that simple. Energy is neither created nor destroyed (at least according to
classical physics). What’s lost from the bullet goes into the animal, all
right, but what isn’t used up breaking tissue structures turns into heat.
Ever wonder why surgeons don’t worry much about leaving a bullet behind,
rather than doing absolutely everything to remove it? Bullet tracks are sterile,
due to the heat generated along the way. What’s that mean? Heat denatures
protein, meaning the structure is changed, and no longer works, either
chemically or architecturally: the tissue is destroyed.
Killing Power
Death results from permanent loss of brain function. This
can be from direct damage to the brain itself, or from damage to other vital
structures, that results in damage to the brain indirectly. We know what those
structures are, and where they are. If we can get a bullet to those structures
with enough undeviating penetration, and inflict enough damage, our objective
will be met.
Energy is fine, but drops off fast. It is not an indicator
of penetration potential, and tells us nothing about directional stability. It
may give us some indication of the amount of damage around the wound channel,
but unless that wound channel blasts through something vital, collateral damage
doesn’t make much difference.
Momentum does tell us something about penetration, and
angular momentum and sectional density tells us about directional stability.
This means:
1) Velocity is less important than worshipers of energy
figures believe,
2) In the same caliber, heavy bullets will carry farther
than light bullets, and stabilize better, and
3) Larger diameter bullets will stabilize better, and
destroy more tissue (other things being equal).
This brings us once again the Taylor KO formula:
KO = mvd
where m is the weight of the bullet in grains,
divided by 7000 grains per pound; v is the velocity in feet per second
("foot seconds" is an incorrect way to talk about bullet velocity, so
don’t say it, unless you want to be ignorant intentionally); and d is
the diameter of the bullet in inches. The reason we are drawn to this formula,
it seems to me, is that it contains all of the elements that are relevant in
determining undeviating penetration and the permanent wound channel.
Now, if we could just understand Stopping Power......