Stopping Power
Stopping power is a colloquial term used to describe the ability of a particular weapon to stop the actions of an individual by means of penetrating ballistic injury. Some theories of stopping power involve concepts such as "energy transfer" and "hydrostatic shock", although there is disagreement about the importance of these effects. Obviously, stopping power is related to the physical properties of the bullet and the effects it has on its target, but the issue is complicated and not easily studied. Critics contend that the importance of "one-shot stop" statistics is overstated, pointing out that most gun encounters do not involve a "shoot once and see how the target reacts" situation.
Many ballistic and forensic experts claim that "stopping power" does not exist, especially with handgun bullets. Stopping is caused not by the force of the bullet, but by the damaging effects of the bullet which are typically a loss of blood, and with it, blood pressure. More immediate effects can result when a bullet strikes a critical organ such as the heart or damages the central nervous system such as the spine or brain. The myth that a human is thrown back by the force of a bullet is false, as Newton's third law dictates. The target and the shooter receive equal and opposite forces, meaning that for a gun to knock a target back, its recoil would have to knock the shooter back an equal amount, which is undesirable.
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History
The concept of "stopping power" appeared in the late 19th Century
when colonial troops (American in the Philippines, British in New
Zealand) engaged in close action with native tribesmen found that
their pistols were not able to stop charging warriors. This led to
larger caliber weapons being developed to stop opponents with a
single round, without necessarily killing them.
Dynamics of bullets
A bullet will destroy or damage any tissues which it penetrates,
leaving a hole behind. It will also cause nearby tissue to stretch
and expand as it passes. These two effects are typically referred to
as permanent cavitation (the hole left by the bullet) and temporary
cavitation (the tissue displaced as the bullet passed).
The degree to which permanent and temporary cavitation occur depend
on the size, shape, and velocity of the bullet. Wider diameter,
blunter shape, higher velocity, or any combination thereof will
increase the width of the permanent and temporary cavitation. This
is because bullets actually crush tissue, not cut it. A bullet with
a rounded or a sharply pointed tip will crush only the tissue
directly in front of a small portion of its diameter; tissue closer
to the edge of the bullet will simply "flow" around it and be pushed
outwards. A blunter, flatter bullet uses more of its face to crush
tissue, but loses velocity more quickly in the process. The depth of
cavitation is based on the same properties, but in a slightly
different way. In this case, it is narrower, more rounded (i.e. more
hydrodynamic) bullets which are able to penetrate more deeply into
tissue.
How much velocity a bullet retains during penetration is very
important. A bullet which starts at a high velocity but loses its
velocity quickly during penetration will crush a relatively large
diameter hole at first, but the permanent cavity will quickly narrow
deeper in. A projectile which retains velocity better (usually a
heavier weight one of the same caliber) might make a smaller hole
than the faster, lighter bullet at first, but retains velocity
better as it penetrates, crushing a deeper hole of larger diameter.
Due to their general design, rifle rounds, which typically have more
mass and vastly higher velocities than handgun rounds, cause much
more temporary cavitation.
None of these processes are static. As a bullet penetrates, it
inevitably loses velocity (and, in the case of expanding bullets,
deforms). This means that the diameter of the temporary and
permanent cavities will gradually get narrower as the bullet
penetrates deeper. In the case of expanding bullets, such as
hollowpoints, the wider diameter and blunter shape temporarily crush
a wider hole and generate a larger temporary cavity, but the bullet
loses velocity even faster, penetrating less.
Some bullets, either because of their high velocity or intended
design, will fragment to some degree. Prefragmented bullets such as
Glaser Safety Slugs and Magsafe ammunition are designed to
completely disintegrate into birdshot and jacketing pieces on impact
with anything, including a person. This is intended to achieve
several things:
1. preventing the bullet from penetrating walls and hitting someone
on the other side,
2. preventing the bullet from ricocheting and continuing to travel
for a long distance,
3. preventing the bullet from overpenetrating a person and striking
someone else.
In this case the individual fragments create a mass of tiny
permanent cavities rather than one large one, and each fragment
generates only a minimal temporary cavity. Fragmentation can occur
with very high velocity bullets, e.g. those fired by rifles. Lead is
a malleable metal; when a softpoint or hollowpoint bullet is
violently deformed fragments can shear off and these will create
small holes around the main one.
Physical effects
Permanent and temporary cavitation cause very different biological
effects. The effects of a permanent cavity are fairly obvious. A
hole through the heart will cause loss of pumping efficiency, loss
of blood, and eventual cardiac arrest. A hole through the brain can
cause instant unconsciousness and is quite likely to kill the
recipient. A hole through an arm or leg which hits only muscle,
however, will cause a great deal of pain but is unlikely to be
fatal, unless a large blood vessel (femoral or brachial arteries,
for example) is also severed in the act.
The effects of temporary cavitation are less well understood, due to
a lack of a test material similar to living tissue. Studies on the
effects of bullets typically experiment on gelatin, in which
temporary cavitation causes radial tears where the gelatin was
stretched. Although such tears are visually engaging, animal tissue
is much more elastic than gelatin, and in most cases temporary
cavitation is unlikely to cause anything more than a slight bruise.
Some speculation states that nerve bundles can be damaged by
temporary cavitation, creating a stunning effect, but this has not
been confirmed experimentally.
One exception to this is when a very powerful temporary cavity
intersects with the spine. In this case, the resulting blunt trauma
can slam the vertebrae together hard enough to either sever the
spinal cord, or damage it enough to knock out, stun, or paralyze the
target. For instance, in the shootout between eight FBI agents and
two bank robbers on April 11, 1986 in Miami, Florida, (see FBI Miami
shootout, 1986) Special Agent Gordon McNeill was struck in the neck
by a high-velocity .223 bullet fired by felon Michael Platt. While
the bullet did not directly contact the spine, and the wound
incurred was not ultimately fatal, the temporary cavitation was
sufficient to render SA McNeill paralyzed for several hours.
Temporary cavitation can also cause the tearing of tissues if a very
large amount of force is involved. The tensile strength of muscle is
roughly 1 to 4 MPa (145 to 580 lbf/inē), and minimal damage will
result if the pressure exerted by the temporary cavitation is below
this. Gelatin and other less elastic media have much lower tensile
strengths, thus they exhibit more damage after being struck with the
same amount of force. At typical handgun velocities, bullets will
create temporary cavities with much less than 1 MPa of pressure, and
thus are incapable of causing damage to elastic tissues which they
do not directly contact.
High velocity fragmentation can also increase the effect of
temporary cavitation. The fragments sheared from the bullet cause
many small permanent cavities around the main entry point. The main
mass of the bullet can then cause a truly massive amount of tearing
as the perforated tissue is stretched. Awareness of this effect and
the suffering it causes is one of the arguments against
high-velocity rifles being used in hunting. It might be noted that
high velocity bullets are usually lighter in weight, and when
striking even something as light as a twig will often break up.
Whether a person or animal will be incapacitated (i.e. 'stopped')
when shot depends on a large number of factors, both physical and
physiological.
Neurological effects
The only way to physiologically stop a person or other animal is to
damage or disrupt their central nervous system (CNS) to the point
that they fall unconscious or die. Bullets can achieve this directly
or indirectly. If a bullet causes sufficient damage to the brain
(particularly the cerebellum or brain stem) or cervical spinal cord,
the CNS damage is direct and nearly instant. However, these targets
are well-protected, very small, and mobile, making them difficult to
hit even under optimal circumstances.
Indirectly, bullets can damage the CNS by way of bleeding. This is
accomplished by putting a large enough hole through a vital blood
vessel or blood-bearing organ. If blood-flow is completely cut off
from the brain, a human still has enough oxygenated blood in their
brain for 10 seconds of willful action. Considering that the higher
brain functions will usually shut down in a life-or-death situation,
this figure might actually be a bit high.
Unless a bullet directly causes damage to a CNS structure, there is
absolutely no physiological reason for a person or animal to be
instantly incapacitated, and unless the bullet crushes a large
enough hole in a major blood vessel or a major blood-bearing organ,
there is no physiological reason for them to be incapacitated at
all.
Psychological effects
Emotional shock, terror, or surprise can cause a person to faint,
surrender, or flee when shot or shot at. Emotional fainting is the
likely reason for most "one-shot stops," and not an intrinsic
quality of any firearm or bullet; there are many documented
instances where suspects have instantly dropped unconscious when the
bullet only hit an extremity, or even completely missed.
Additionally, the muzzle blast and flash from many firearms are
substantial and can cause disorientation, dazzling, and stunning
effects; flashbangs and other less-lethal "distraction devices" rely
exclusively on these.
Pain is another psychological factor, and can be enough to dissuade
a person from continuing their actions.
Temporary cavitation can emphasize the impact of a bullet, since the
resulting tissue compression is identical to simple blunt trauma.
It's easier for someone to feel that they've been shot if there is
considerable temporary cavitation, and this can contribute to either
psychological factor of incapacitation.
However, if a person is sufficiently enraged, determined, or
intoxicated they can simply shrug off any psychological effects of
being shot; therefore, such effects are not as reliable as
physiological effects at stopping people. Animals will not faint or
surrender if injured, though they may be frightened by the loud
noise and pain of being shot, so psychological mechanisms are even
less effective against non-humans.
Industry penetration requirements
According to Dr. Martin Fackler and the IWBA, between 12.5 and 14 in
(318 and 356 mm) of penetration in calibrated tissue simulant is
optimal performance for a bullet which is meant to be used
defensively, against a human adversary. They also believe that
penetration is one of the most important factors when choosing a
bullet (and that the number one factor is shot placement); if the
bullet penetrates less than their guidelines, it is inadequate, and
if it penetrates more, it is still satisfactory though not optimal.
The FBI's penetration requirement is very similar at 12 to 18 in
(305 to 457 mm).
12.5 and 14 in (318 and 356 mm) might seem like a lot until you
consider that a bullet sheds velocity--and crushes a narrower
hole--as it penetrates, so the bullet might be crushing a very small
amount of tissue during its last two or three inches of travel,
giving only between 9.5 and 12 in of effective penetration. Also,
skin is elastic and tough enough that it can cause a bullet to be
retained in the body, even if the bullet had a relatively high
retained velocity when it hit the skin. About 250 ft/s (76 m/s)
velocity is required for an expanded hollowpoint bullet to puncture
skin 50% of the time.
The IWBA's and FBI's penetration guidelines are to ensure that the
bullet can reach a vital structure from most angles, and retain
enough velocity to punch a large enough hole through it.
Overpenetration
Overpenetration is often exaggerated by those who advocate
shallow-penetrating "rapid energy transfer" bullets. Tests have
shown that human skin, on the entry side, can resist penetration as
much as 2" (5 cm) of muscle, and skin on the exit side can be the
equivalent of up to 4 in (10 cm). A bullet would need to penetrate
greater than approximately 15 in (38 cm) of tissue simulant to have
a chance to completely perforate a 9" (23 cm) thick torso, and would
need to penetrate more than 17 in (43 cm) to actually pose a serous
threat to people downrange.
Even if the bullet does completely penetrate a person, it will have
a very reduced velocity and probably no longer be ballistically
stable. Missing the intended target altogether, thereby leaving a
full velocity bullet to harm whatever is in its path, is a much
greater threat.
A hit on a less dense peripheral body area, such as a limb, does
present a more serious risk of overpenetration however. Penetration
of walls and other cover is also a consideration for police and
urban use.
According to NYPD SOP-9 (Standard Operating Procedure #9) data, in
the year 2000, only 9% of shots fired by officers engaged in
gunfights actually hit perpetrators. In the same year, there were a
total of 129 "shooting incidents" (including non-gunfights, such as
officers firing at aggressive dogs, unarmed or fleeing perpetrators,
etc.), 471 total shots fired by officers, 367 shots fired at
perpetrators, and 58 total hits on perpetrators by police. So when
non-gunfight shooting data is added, the rate at which police hit
what they aim at in real life situations is still only 15.8%. Given
that none of those misses resulted in injury to an innocent third
party, it is very unlikely for someone to be injured by a bullet
that passes through the intended target.
Other hypotheses of stopping power
These hypotheses are used mostly in marketing of bullets and
firearms, and are not considered scientific.
Hydrostatic shock
Hydrostatic shock is a theory of terminal ballistics that wounding
effects are created by a shock wave in the tissues of the target.
Energy transfer
The energy transfer hypotheses states that the more energy is
transferred to the target, the greater the effect.
This theory is frequently referred to by Kennedy assassination
theories, who cite the Zapruder film, which shows Kennedy's head
recoiling backwards from a shot, as evidence that therefore, that
shot must have been fired from in front of the limousine rather than
from behind, where Lee Harvey Oswald was firing from the Texas
School Book Depository, implying a second assassin. However, it has
been repeatedly demonstrated, most recently to a large television
audience by Penn and Teller on May 9, 2005 on their Showtime network
program, Bullshit!, that when a simplified physical model of a brain
inside a skull, composed of a melon wrapped with strapping tape, is
shot in a similar fashion, the melon recoils backwards, towards the
gun; evidence that the actual transfer of energy from a bullet
passing through a complex object is much more complex than simple
mathematical models based on oversimplified physical assumptions can
predict, a priori.
One-shot stop
This hypothesis is based solely on statistics. It considers the
history of shooting incidents, and compiles the percentage of "one
shot stops" achieved with a given firearm. That percentage is then
supposed to be the chance of that firearm getting a "one shot stop".
For example, if an assailant uses a new combination of firearm and
bullet for the first time, shooting 10 people and incapacitating all
but two with one shot, the one-shot stop percentage for the
combination would be 80%.
The problem with this is that the hypothesis ignores any inherent
selection bias. For example, high-velocity 9 mm hollowpoint rounds
appear to have the highest percentage of one-shot stops. Rather than
identifying this as an inherent property of the firearm-bullet
combination, the situations where these have occurred need to be
considered. The 9 mm has been the preferred caliber of many police
departments, so many of these one-shot stops were probably made by
well-trained police officers, where accurate placement would be a
contributory factor.
Critics of this theory point out that bullet placement is a very
significant factor, but is unused in such calculations.
Ethical discussion
While development of guns and ammunition is mainly focused on
causing as much damage to the target as possible, there are also
ethical arguments against this. As described above, a larger
stopping power almost inevitably causes larger damage to the person
who has been hit, therefore increasing the danger of killing or
permanently disabling the assailant. Many types of tissue, including
nervous and muscle tissue, cannot be regenerated. Destroyed cells of
these are lost forever. This must be balanced against the risk of
the police, or an armed citizen acting in defense of his life,
permitting an assailant to continue his violent and unethical
behavior, normally directed against those who are unable or
unwilling to defend themselves.
A larger permanent cavity increases the chance of vital structures
being damaged or destroyed. A shot through the heart or another
primary blood vessel is lethal in most cases, mainly due to rapid
loss of blood. Furthermore, damage to the central nervous system
often results in permanent disabilities, e.g. amnesia, loss of
eyesight or mental disability, and damage to the spinal cord may
result in paraplegia. But also injuries to non-vital parts of the
body may be permanent. Especially expanding or fragmenting
projectiles affect a large volume of tissue which, in many cases,
cannot regenerate, even with modern surgical treatment.
Despite this, being shot with a handgun is fatal only about 5% of
the time, and result in serious medical damage approximately 15% of
the time. It has even been estimated that survival rates after being
shot in the heart are roughly 50%. This is because the lower heart
structure is simple, and holes may be stitched closed, while holes
in the upper heart structure damage valves which are complex and
hard to repair.
Modern police firearms are chosen so that even an intoxicated, large
and strong, or otherwise resilient assailant can be stopped.
Consequently, they may be oversized for the less robust, especially
juveniles, and the risk of serious permanent damage is increased for
these people. On the other hand, as discussed in the sections above,
even a huge destruction of tissue or even of vital organs is no
guarantee of instantaneous incapacitation; massive damage to the
central nervous system is the only means by which people can be
reliably stopped.
For ethical reasons, in some countries full metal jacket bullets are
standard issue for the police. In Germany, however, they now have
been largely replaced by expanding bullets; and in many places in
America, it is illegal for the police to use anything but
hollowpoint ammunition. The use of full metal jacket ammunition
presents greater risk of overpenetration, particularly of walls,
vehicles, or other cover. The reduced probability of rapid
incapacitation of an assailant is also a consideration, presenting
potentially a greater risk to peace officers and civilians. Full
metal jacket ammunition may also require more shots than expanding
ammunition to have the same effect on a person, and many small holes
are generally harder to surgically repair than a smaller number of
larger ones.
In the United States, highway patrol agencies and other state police
agencies are often more likely to arm their officers with more
powerful ammunition, such as +P ammunition, as officers in these
agencies are more likely to shoot at longer ranges, face a longer
response time for backup in the event of a dangerous situation, and
less likely to have civilians backgrounding their target than urban
police.
The military use of hollow point bullets is prohibited under the
Hague Convention of 1899 as they are designed to "expand or flatten
easily in the human body". This prohibition naturally applies only
to the armed forces of signatory nations.
Although frequently postulated as possible alternatives to firearm
use by police, "non-lethal" weapons such as OC spray (pepper spray),
rubber and "beanbag" projectiles, clubs, and electrical stun devices
are not always acceptable. When a device is labeled as "non-lethal,"
some people become more inclined to use them irresponsibly.
Furthermore, many "non-lethal" weapons can and have actually killed
their target; this has led to them being more popularly called "less
lethal." Of these types of weapons, Tasers and other electrical stun
devices have possibly the worst reputation. While police officers
often use tasers to defend themselves and others, there have been
several, very publicized cases where tasers have been used not in
self defense, but to gain cooperation from a non-violent suspect; an
action that could be viewed as torture.
For instance, the Israeli military once used suppressed Ruger 10/22
rifles as a "non-lethal" means of stopping riots; snipers were
instructed to shoot riot leaders in the legs from a distance, ending
the problem with minimal bloodshed. Many snipers assumed that since
the suppressed 10/22 was considered "non-lethal," they could shoot
their target anywhere and have the same result. After several people
were killed due to thoracic and abdominal wounds, the Israeli
military stopped issuing 10/22s for this purpose.