Stopping power

Categories: Articles to be merged | Ballistics | Pseudoscience

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 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. It is a myth that handgun bullets "knock down" a human target or that a human is thrown back by the force of a handgun bullet.

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History

The concept of "stopping power" appeared in the late 19th Century when colonial troops (American in the Philippines, British Empire 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.

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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 sharp 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 deeper 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 larger diameter hole deeper.

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 penetrating 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. Another category is a bullet designed in the late 1960's is the Cup-point. This bullet design had a shallow semi-circle depression with a narrow flat edge something like a reversed wadcutter. This bullet when compared to others in gelatin block tests, did not leave an entrance hole or an exit hole. This bullet disintegrated the entire gelatin block implying tremendous shock power.

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Biological 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 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.

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, 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/in²), 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 in many cases are usually lighter in weight, and often when striking even something as light as a twig will often break up. For this reason they don't pose such a danger down range. While not a certainty high velocity bullets in wooded areas are a little safer than realized.

Whether a person or animal will be incapacitated (i.e. ‘’’stopped’’’) when shot depends on a large number of factors, both psychological and physiological.

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Physiological effects

The only way to physiologically stop a person 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 a person's higher brain functions will usually shut down in a life-or-death situation, this figure might actually be a bit low.

Unless a bullet strikes and damages a CNS structure, there is absolutely no physiological reason for a person 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.

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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 they are not as reliable as physiological effects at stopping people.

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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, and penetration is one of the most important factors when choosing a bullet (and the number one factor is shot placement); if the bullet penetrates less it is inadequate, and if it penetrates more, it is satisfactory. 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. Tests have also shown that human skin , by virtue of its high tensile strength and elasticity, can resist penetration by projectiles about as much as 2 in (51 mm) of muscle tissue, further reducing the effective penetration.

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.

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Overpenetration

Overpenetration is exaggerated by those who advocate shallow-penetrating "rapid energy transfer" bullets. Tests have shown that human skin, on the entry side, resists penetration about as much as 2" (5 cm) of muscle, and skin on the exit side is the equivalent of 4 in (10 cm). A bullet would need to penetrate greater than 14 in (36 cm) of tissue simulant to have a chance to completely perforate an 8" (20 cm) thick torso.

Even if the bullet does completely penetrate a person, it would probably have very little velocity left by that point, and pose a reduced risk to those downrange. Missing altogether is a much greater threat.

And 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%.

When you consider the staggering miss rate of police officers, it is very unlikely that a bullet will hit someone else after going through an attacker. Accidental shootings due to misses have occurred, but at a far lower rate than that at which officers miss their intended target.

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Other hypotheses of stopping power

These hypotheses are used mostly in marketing of bullets and firearms, and are not considered scientific.

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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.

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Energy transfer

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It has been suggested that this article or section be merged with energy transfer. (Discuss)

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.

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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 a 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.

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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 aguments 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.

A larger permanent cavity increases the chance for vital structures of 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%.

Modern police firearms are chosen so that even an intoxicated, large and strong, or otherwise resiliant 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. This is also why full metal jacket bullets are used in warfare; there is said to be a significant moral difference between an enemy soldier, who is serving his country, and a criminal, who is harming others for their own personal gain. However, this is not a legitimate justification for the choice of weapons since judgement is reserved to judiciary in democratic countries.

Unfortunately, non-lethal weapons such as OC spray (pepper spray), rubber and "beanbag" projectiles, clubs, and electrical stun devices are not always acceptable alternatives to firearms. When a device is labeled as "non-lethal," some people become more inclined to use them irresponsibly.

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.

Similarly, a number of people in America and other countries have been killed by "beanbag" and rubber "less-lethal" projectiles which struck them in the chest, head, or throat, when police were unable or unwilling to aim for the proper areas--the abdomen, buttocks, and legs.

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.

In one instance, a man was tasered for refusing to incriminate himself by giving a urine sample. In another, a wheelchair-bound, 75 year old woman was tasered when she allegedly swung her arm at a police officer. In a third case, a Marine reservist was tasered, despite having his hands raised, because he would not turn around.

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