Science Fair Project Encyclopedia
Stopping power is a colloquial term used to describe how much being shot by a particular gun will slow someone down. Most theories about stopping power rely on impressive-sounding yet meaningless terminology—such as "energy transfer" and "hydrostatic shock"—to hide the fact that they have minimal basis in physics. In reality, stopping power is simply related to the physical properties of the bullet and the effects it has on its target.
The idea of "stopping power" appeared in the late 19th Century when colonial troops (American in the Philipines, 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 calibre weapons being developed to drop (NB: not necessarily kill, just stop) opponents with a single round.
Stopping power may be defined as the ability of a particular weapon to disable (but not necessarily kill) the target so that they are no longer a threat ("hors de combat"). As such it has a direct bearing one the survivability of the military or law enforcement (Police) personnel using that weapon. For example, during a bank robbery in Los Angeles in 1997, the LAPD, armed with pistols and shotguns, traded gunfire with two men clad in body armor and firing AK-47s (an assault rifle). The disadvantaged police had to go to a nearby gun store to obtain AR 15s so that they could have more powerful rifles.
There are several factors that influence stopping power.
The first is that, no matter what the energy level or design of a bullet, if the bullet misses or just grazes the target then there is zero “stopping power”. In other words, stopping power is relative to where the bullet hits the target. Consider an imaginary line from the top of the head to the navel. The area four inches on each side of that line is the zone of “stopping power” since it contains most of the major organs of the body – brain, throat, spinal cord, heart, lungs, stomach, etc. Bullet penetration into any of these areas would be deadly / disabling. However, even if a bullet should miss this zone and hit, for example, an arm or leg, it could still cause a disabling / deadly wound by crushing bone or severing a major blood vessel. Associated with the level of penetration is to what extent a bullet yaws (tumbles) or fragments upon impact. Such an action by a bullet increases the area or cavity created by the penetration, thereby increasing the probability of a disabling / deadly wound.
“Stopping power” is also a factor of distance from shooter to target. Does the bullet have enough energy to make a sufficient penetration of the body at a given distance? If a shooter fires a .45 cal or a .30-06 bullet at a target 20 ft (6 m) away and hits the “zone”, the wound would be deadly / disabling. But, if a shooter fires a .45 cal or .30-06 bullet at a target 300 yards (300 m) away, only the latter has the possiblity of creating a wound that would be deadly / disabling.
Another example would be comparing two calibers fired from the same length barrel at a given distance. The standard NATO round is the 5.56 x 45 with a 62 gr (4 g) bullet. At present, the US is developing a 6.8 x 43 round with a 115 gr (7 g) bullet. At 300 yd (300 m), the former has an energy of 640 ft.lbf (868 J) while the latter has an energy of 1075 ft.lbf (1458 J). Also, are there any obstacles between the shooter and the target? If so, which bullet can penetrate the obstacle and retain enough energy to inflict a deadly / incapacitating wound on the target.
Dynamics of bullets
A bullet will destroy or damage any Biological 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:
- preventing the bullet from penetrating walls and hitting someone on the other side,
- preventing the bullet from ricocheting and continuing to travel for a long distance,
- 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 maaleable 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 60's is the Cup-point . This bullet design had a shallow simi-circle depression with a narrow flat edge something like a reversed wad cutter . 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.
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 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. Studied 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 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 usally ligher 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 incapacitate (i.e. ‘’’stopped’’’) when shot depends on a large number of factors, both psychological and physiological.
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.
Emotional shock, terror, and surprise can cause a person to faint when shot. This is the likely reason for most "one-shot stops," and not an intrinsic quality of any firearm or bullet. The realization that one has been shot or even shot at is also often enough to cause a person to give up or flee. Temporary cavitation can also 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 psychological factors of incapacitation (above).
Pain is another psychological factor, and can be enough to dissuade a person from doing anything but screaming. If the victim is sufficiently enraged, determined, or intoxicated however, they can simply shrug off any psychological effects of being shot, so they should not be counted on to stop an attacker.
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.
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" of muscle, and skin on the exit side is the equivalent of 4 in (102 mm). A bullet would need to penetrate greater than 14 in of tissue simulant to have a chance to completely perforate an 8" 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.
Other hypotheses of stopping power
These hypotheses are used mostly in marketing of bullets and firearms, and are not considered scientific.
This hypothesis states that the more hydrostatic shock a bullet generates in a target, the greater the effect. The term "hydrostatic shock" itself is quite nonsensical. Hydro - water; static - remaining still; shock - a rapid, violent motion; hydrostatic shock - water that moves while remaining still. It refers mostly to the effect of temporary cavitation, with can produce quite impressive effects in non-elastic test mediums such pot roasts, watermelons, and clay. In those mediums, however, the temporary cavitation becomes permanent, while in elastic, living tissue it rarely causes much of an effect.
The energy transfer hypotheses states that the more energy is transferred to the target, the greater the effect.
Which is deadlier, a 50 oz (1.42 kg) basketball thrown at a relatively modest 59.4 mph (95 km/h), or a 1 pound (454 gram) brick falling from a height of 14 feet 3 inches (4.4 m)? Most will answer the brick. More people are killed by falling bricks than thrown basketballs, right?
(For the UK note: a standard red brick, 8 by 4 by 3 in, weighs over 2 kg)
Well, the basketball has the equivalent kinetic energy of a .45 caliber (11.43 mm), 230 grain (14.9 g) bullet at 850 feet per second (259 m/s); about 369 ft.lbf (500 J). The brick has the kinetic energy of a .177 caliber (4.5 mm) steel BB at 500 feet per second (152 m/s), only 3.2 ft.lbf (4.32 J). Either is quite capable of damaging a human head, or bouncing off with minimal injury. Identical effect, yet very disparate amounts of "energy transfer."
Of course, the above example is rather ludicrous – sort of a trick question / answer type of presentation rather than an accurate description of the deadly effect of a bullet. First of all, a bullet is not in the shape of basketball or of a brick but in a design that will penetrate a human being. Secondly, the .45 caliber, 230 grain (15 g) bullet that has the energy of 369 ft.lbf (500 J) is the muzzle velocity listed in most ballistic tables. If a person’s head is situated in front of a .45 caliber muzzle when it is fired, the effect would be quite deadly and it is definite that they will be “stopped”.
Evidently a major arms maker, Heckler & Koch, gives credence to the idea of “stopping power”. Their MP5 submachine gun, used for years by many SWAT and military tactical units, fired the standard 9mm parabellum [.36 cal] NATO cartridge. However, in response to requests by users for a cartridge with increased terminal effects on target, H&K offered a new model of the MP5 that fired the 10 mm Auto cartridge [.40 cal]. This cartridge provides up to twice the muzzle energy of the standard 9 mm parabellum.
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 skew. 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 9mm 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.
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; literally using them to torture a suspect into compliance.
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.
- Firearms Tactical Institute
- Wound Ballistics
- Reality of the Street? A Practical Analysis of Offender Gunshot Wound Reaction for Law Enforcement
- Handgun Wounding Factors and Effectiveness
- Ballistic gelatin testing done by "GoldenLoki"
- The AR-15.com Ammo Oracle
- B&T Ammo Labs
- A forum posting linking to several journal articles by Martin Fackler, M.D.
- Tactical Forums
- What We Didn't Know Hurt Us
- Virtual Naval Hospital - Emergency War Surgery
- One Shot Drops - Surviving the Myth
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