Stopping power Stopping power is the ability of a firearm or other weapon to cause a penetrating ballistic injury to a target ( human or animal ) enough to incapacitate the target where it stands . This contrasts with lethality in that it pertains only to a weapon ' s ability to incapacitate quickly , regardless of whether death ultimately ensues . Some theories of stopping power involve concepts such as " energy transfer " and " hydrostatic shock " , although there is disagreement regarding the importance of these effects . Stopping power is related to the physical properties of the bullet and the effect 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 . Stopping is usually caused not by the force of the bullet ( especially in the case of handgun and rifle bullets ) , 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 damages parts of the central nervous system , such as the spine or brain . In response to addressing stopping power issues , the Mozambique Drill was developed to maximize the likelihood of a target ' s quick incapacitation . A manstopper is any combination of firearm and ammunition that can reliably incapacitate , or " stop " , a human target immediately . For example , the . 45 ACP pistol round and the . 357 Magnum revolver round both have firm reputations as " manstoppers . " Historically , one type of ammunition has had the specific tradename " Manstopper . " Officially known as the Mk III cartridge , these were made to suit the British Webley . 455 service revolver in the early 20th century . The ammunition used a cylindrical bullet with hemispherical depressions at both ends . The front acted as a hollow point deforming on impact while the base opened to seal the round in the barrel . It was introduced in 1898 for use against " savages " , but fell quickly from favour due to concerns of breaching the Hague Convention ' s international laws on military ammunition , and was replaced in 1900 by re - issued Mk II pointed - bullet ammunition . Some sporting arms are also referred to as " stoppers " or " stopping rifles . " These powerful arms are often used by game hunters ( or their guides ) for stopping a suddenly charging creature , like a buffalo or an elephant . History . The concept of stopping power appeared in the 19th Century when colonial troops ( e . g . American in the Philippines during the Moro Rebellion , British in New Zealand during the Land Wars ) , engaging in close action with native tribesmen , found that their pistols were not able to stop charging warrior s . This led to larger caliber weapons ( such as the . 45 Colt being returned to service , and the . 45 ACP being developed ) , intended to stop opponents with a single round . During the Seymour Expedition in China , at one of the battles at Langfang , Chinese Boxer s , armed with swords and spears , charged the British and Americans , who were armed with guns . At point blank range , one British soldier had to empty four bullets into a Boxer before he stopped , and the American Captain Bowman McCalla reported that single rifle shots were not enough , multiple rifle shots were needed to halt a Boxer . Only machine guns were effective in stopping the Boxers . British troops used expanding bullet s against native tribesmen in the Northwest Frontier of India , and in the Sudan ( see The River War by Winston Churchill ) . Hence Britain voted against a prohibition on their use at the Hague Convention of 1899 , although the prohibition only applied to " international warfare " . Dynamics of bullets . A bullet will destroy or damage any tissues which it penetrates , creating a wound channel . It will also cause nearby tissue to stretch and expand as it passes through tissue . These two effects are typically referred to as " permanent cavity " ( the track left by the bullet as it penetrates flesh ) and " temporary cavity , " which , as the name implies , is the temporary ( instantaneous ) displacement caused as the bullet travels through flesh and is many times larger than the actual diameter of the bullet . These phenomena are unrelated to low - pressure cavitation in liquids . The degree to which permanent and temporary cavitation occur is dependent on the mass , diameter , material , design and velocity of the bullet . This is because bullets " crush " tissue , and do not cut it . A bullet constructed with a half diameter ogive designed meplat and hard , solid copper alloy material will crush only the tissue directly in front of the bullet . This type of bullet ( monolithic - solid rifle bullet ) is conducive to cause more temporary cavitation as the tissue flows around the bullet , causing a deep and narrow wound channel . A bullet constructed with a two diameter , hollow point ogive designed meplat and low - antimony lead - alloy core with a thin gilding metal jacket material will crush tissue in front and to the sides as the bullet expands . Due to the energy expended in bullet expansion , velocity is lost more quickly . This type of bullet ( hollow - point hand gun bullet ) is conducive to causing more permanent cavitation as the tissue is crushed and accelerated into other tissues by the bullet , causing a shorter and wider wound channel . Bullets are constructed to behave in different ways , depending on the intended target . Different bullets are constructed variously to : not expand upon impact , expand upon impact at high velocity , expand upon impact , expand across a broad range of velocities , expand upon impact at low velocity , tumble upon impact , fragment upon impact , or disintegrate upon impact . To control the expansion of a bullet , meplat design and materials are engineered . The meplat designs are : flat ; round to pointed depending on the ogive ; hollow pointed which can be large in diameter and shallow or narrow in diameter and deep and truncated which is a long narrow punched hole in the end of a monolithic - solid type bullet . The materials used to make bullets are : pure lead ; alloyed lead for hardness ; gilding metal jacket which is a copper alloy of nickel and zinc to promote higher velocities ; pure copper ; copper alloy of bronze with tungsten steel alloy inserts to promote weight . Some bullets are constructed by bonding the lead core to the jacket to promote higher weight retention upon impact , causing a larger and deeper wound channel . Some bullets have a web in the center of the bullet to limit the expansion of the bullet while promoting penetration . Some bullets have dual cores to promote penetration . Bullets that might be considered to have stopping power for dangerous large game animals are usually 11 . 63 mm ( . 458 caliber ) and larger , including 12 - gauge shotgun slugs . These bullets are monolithic - solids ; full metal jacketed and tungsten steel insert . They are constructed to hold up during close range , high velocity impacts . These bullets are expected to impact and penetrate , and transfer energy to the surrounding tissues and vital organs through the entire length of a game animal ’ s body if need be . Bullets with sufficient stopping power for humans are generally large caliber , 9 . 07 mm ( . 357 caliber ) handgun bullets of hollow point design . Pre - fragmented bullets such as Glaser Safety Slug s and MagSafe ammunition are designed to fragment into birdshot on impact with the target . This fragmentation is intended to create more trauma to the target , and also to reduce collateral damage caused from ricocheting or overpenetrating of the target and the surrounding environments such as walls . Fragmenting rounds have been shown to be unlikely to obtain deep penetration necessary to disrupt vital organs located at the back of a hostile human . Wounding effects . Physical . 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 liver or lung will be similar , with the lung shot having the added effect of reducing blood oxygenation ; these effects however are generally slower to arise than damage to the heart . A hole through the brain can cause instant unconsciousness and will likely kill the recipient . A hole through the spinal cord will instantly interrupt the nerve signals to and from some or all extremities , disabling the target and in many cases also resulting in death ( as the nerve signals to and from the heart and / or lungs are interrupted by a shot high in the chest or to the neck ) . By contrast , a hole through an arm or leg which hits only muscle will cause a great deal of pain but is unlikely to be fatal , unless one of the large blood vessels ( femoral or brachial arteries , for example ) is also severed in the process . The effects of temporary cavitation are less well understood , due to a lack of a test material identical to living tissue . Studies on the effects of bullets typically are based on experiments using ballistic gelatin , in which temporary cavitation causes radial tears where the gelatin was stretched . Although such tears are visually engaging , some animal tissues ( other than bone or liver ) are more elastic than gelatin . In most cases , temporary cavitation is unlikely to cause anything more than a bruise . Some speculation states that nerve bundles can be damaged by temporary cavitation , creating a stun effect , but this has not been confirmed . 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 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 ranges roughly from 1 to 4 MPa ( 145 to 580 lbf / in ) , 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 . Core - locked rifle bullets that strike a major bone ( such as a femur ) can expend their entire energy into the surrounding tissue , causing it to take on a gelled consistency as the cellular structure is destroyed . The struck bone is commonly shattered at the point of impact . 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 . Whether a person or animal will be incapacitated ( i . e . " stopped " ) when shot , depends on a large number of factors , including physical , physiological , and psychological effects . Neurological . The only way to immediately incapacitate a person or animal is to damage or disrupt their central nervous system ( CNS ) to the point of paralysis , unconsciousness , or death . Bullets can achieve this directly or indirectly . If a bullet causes sufficient damage to the brain or spinal cord , immediate loss of consciousness or paralysis , respectively , can result . However , these targets are relatively small and mobile , making them extremely difficult to hit even under optimal circumstances . Bullets can indirectly disrupt the CNS by damaging the cardiovascular system so that it can no longer provide enough oxygen to the brain to sustain consciousness . This can be the result of bleeding from a perforation of a large blood vessel or blood - bearing organ , or the result of damage to the lungs or airway . If blood flow is completely cut off from the brain , a human still has enough oxygenated blood in their brain for 10 – 15 seconds of wilful action , though with rapidly decreasing effectiveness as the victim begins to lose consciousness . Unless a bullet directly damages or disrupts the central nervous system , a person or animal will not be instantly and completely incapacitated by physiological damage . However , bullets can cause other disabling injuries that prevent specific actions ( a person shot in the femur cannot walk ) and the physiological pain response from severe injuries will temporarily disable most individuals . Several scientific papers reveal ballistic pressure wave effects on wounding and incapacitation , including central nervous system injuries from hits to the thorax and extremities . These papers document remote wounding effects for both rifle and pistol levels of energy transfer . Recent work by Courtney and Courtney provides compelling support for the role of a ballistic pressure wave in creating remote neural effects leading to incapacitation and injury . This work builds upon the earlier works of Suneson et al . where the researchers implanted high - speed pressure transducers into the brain of pigs and demonstrated that a significant pressure wave reaches the brain of pigs shot in the thigh . These scientists observed neural damage in the brain caused by the distant effects of the ballistic pressure wave originating in the thigh . The results of Suneson et al . were confirmed and expanded upon by a later experiment in dogs which " confirmed that distant effect exists in the central nervous system after a high - energy missile impact to an extremity . A high - frequency oscillating pressure wave with large amplitude and short duration was found in the brain after the extremity impact of a high - energy missile . . . " Wang et al . observed significant damage in both the hypothalamus and hippocampus regions of the brain due to remote effects of the ballistic pressure wave . Psychological . 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 effectiveness quality of any firearm or bullet ; there are many documented instances where people 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 ( stun grenades ) and other less - lethal " distraction devices " rely exclusively on these effects . 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 force trauma . It is easier for someone to feel when they have 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 the psychological effects of being shot . During the colonial era when native tribesmen came into contact with firearms for the first time , there was no psychological conditioning that being shot was fatal , and most colonial powers eventually sought to create more effective man stoppers . Therefore , such effects are not as reliable as physiological effects at stopping people . Animals will not faint or surrender if injured , though they may become frightened by the loud noise and pain of being shot , so psychological mechanisms are generally less effective against non - humans . Penetration . According to Dr . Martin Fackler and the International Wound Ballistics Association ( IWBA ) , between 12 . 5 and 14 inches ( 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 inches ( 305 to 457 mm ) . A penetration depth of 12 . 5 to 14 inches ( 318 and 356 mm ) may seem excessive , but a bullet sheds velocity — and crushes a narrower hole — as it penetrates deeper , while losing velocity , so the bullet might be crushing a very small amount of tissue ( simulating an " ice pick " injury ) during its last two or three inches of travel , giving only between 9 . 5 and 12 inches of effective wide - area penetration . Also , skin is elastic and tough enough to cause a bullet to be retained in the body , even if the bullet had a relatively high velocity when it hit the skin . About 250 ft / s ( 76 m / s ) velocity is required for an expanded hollow point 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 , while retaining enough velocity to generate a large diameter hole through tissue . An extreme example where penetration would be important is if the bullet first had to enter and then exit an outstretched arm before impacting the torso . A bullet with low penetration might embed itself in the arm whereas a higher penetrating bullet would penetrate the arm then enter the thorax where it would have a chance of hitting a vital organ . Overpenetration . Overpenetration is when a bullet passes through its target and out of the other side , potentially going on to damage something or someone else . Over - penetration also denies the bullet its ability to fully " dump " its energy inside the intended target . Other hypotheses . These hypotheses are a matter of some debate among scientists in the field : Energy transfer . The energy transfer hypothesis states that the more energy that is transferred to the target , the greater the destructive potential . Energy is a function of mass and the square of velocity . Generally speaking , it is the intention of the shooter to deliver an adequate amount of energy to the target via the projectile / s . Projectiles such as rifle bullets , high velocity handgun bullets and shotgun slugs can over - penetrate . Projectiles such as handgun bullets and shot can under - penetrate . Projectiles that reach the target with too low a velocity or bird shot may not penetrate at all . All the above conditions affect energy transfer . Over - penetration is detrimental to stopping power in regards to energy . This is because a bullet that passes through the target does not transfer all of its energy to the target . Despite decreased tissue damage due to loss of transferred energy on an over - penetrating shot , the resulting exit wound would cause increased blood loss and therefore a decrease in blood pressure in the victim . This effect on both persons and game animals is likely to be incapacitating over the length of the entire shooting event . Under - penetration is also detrimental to stopping power . Projectile / s that do not transfer enough energy to the target may fail to create a fatal wound cavity . Also vital organs may not be reached , thereby limiting the amount of tissue damage , blood loss , and / or loss of blood pressure . Non - penetration of projectile / s may only deliver enough energy to create bruising , punctures and or blunt force trauma . All of which may result in internal injury solely through the force of the impact but not stop the target . A notable example of projectiles designed to deliver stopping power without target penetration are Flexible baton round s ( commonly known as " beanbag bullets " ) , a type of reduced - lethality ammunition . As mentioned above , there are many factors that affect " stopping power . " Within this theory energy transfer is related to destructive potential ; however , the importance of energy transfer in determining the stopping power of projectiles ( when compared to other factors like location of the wound and wound cavity size ) is a controversial topic . The force exerted by a projectile upon tissue is equal to the bullet ' s local rate of kinetic energy loss , with distance formula _ 1 ( the first derivative of the bullets kinetic energy with respect to position ) . The ballistic pressure wave is proportional to this retarding force ( Courtney and Courtney ) , and this retarding force is also the origin of both temporary cavitation and prompt damage ( CE Peters ) . 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 . It is argued that evidence of such shock can be seen in ultra - high - speed images of supersonic bullets passing through various objects such as fruit ; the fruit explodes due to the shock waves caused by the bullet passing through at high speed . Proponents of the theory contend that damage to the brain from hydrostatic shock from a shot to the chest occurs in humans with most rifle cartridges and some higher - velocity handgun cartridges . Knockback . The idea of " knockback " is a subset or simplification of energy transfer theory , and states that a bullet of sufficient caliber at sufficient speed which transfers all its energy to a subject has enough force , by sheer momentum of the bullet , to stop forward momentum of an attacker and knock them backwards or downwards . The idea was first widely expounded in ballistics discussions during American involvement in Philippine insurrections and , simultaneously , in British involvement in the Caribbean , when front - line reports stated that the . 38 caliber revolvers carried by U . S . and British soldiers were incapable of bringing down a charging warrior . Thus , in the early 1900s , the U . S . reverted to the . 45 Colt in single action revolvers , and later adopted the . 45 ACP cartridge in what was to become the M1911A1 pistol and the British adopted the . 455 Webley caliber cartridge in the Webley Revolver . The larger cartridges were chosen largely due to the Big Hole Theory ( a larger hole does more damage ) , but the common interpretation was that these were changes from a light , deeply penetrating bullet to a larger , heavier " manstopper " bullet . Though popularized in television and movies , and commonly referred to as " true stopping power " by novice or uneducated proponents of large powerful calibers such as . 44 Magnum , the effect of knockback from a handgun and indeed most personal weapons is largely a myth . The momentum of the so - called " manstopper " . 45 ACP bullet is approximately that of a mass dropped from a height of . Such a force is simply incapable of arresting a running target ' s forward momentum . In addition , bullets are designed to penetrate instead of strike a blunt force blow , because , in penetrating , more severe tissue damage is done . A bullet with sufficient energy to knock down an assailant , such as a high - speed rifle bullet , would be more likely to instead pass straight through , while not transferring the full energy ( in fact only a very small percentage of the full energy ) of the bullet to the victim . The " knockback " effect is however commonly " seen " in real - life shootings , and can be explained by physiological and psychological means . Humans encountering a physical hit , be it a punch or a bullet , are conditioned to absorb the blow by moving in the same direction as the force . The physical effect against a non - penetrating weapon is to reduce the force felt by the blow , and in addition , retreating from an attack increases the distance such an attack must cover , which in the case of non - projectile weapons such as fists or a knife , places the target out of range of further attack . In addition , there is a theoretical sociological explanation , that in modern civilization , with far greater separation by most individuals from violence , hunting , and combat , normal individuals may simply recoil , buckle , or fall backward when hit by a bullet , even when in pure physiological terms they are perfectly capable of continuing to charge . Although knockback is not possible with a handgun bullet , it can be an actual effect occurring in reaction to being hit by a massive slug , such as a rubber bullet or sandbag fired from a shotgun . The dynamics of a slug round are quite different than penetrating bullets ; the projectile is here designed not to penetrate but instead to strike a hard , blunt force blow , and as the momentum carried by a shotgun cartridge is greater than practically any production handgun cartridge , the force imparted is comparable to a hard punch and is capable , by physics , of affecting a person ' s forward motion . In any case , due to conservation of momentum , the gun ' s recoil is always larger than the bullet ' s knockback , as some momentum of the bullet is lost during flight , and if the bullet penetrates through the target it will not have imparted all its momentum into the target . One - shot stop . This hypothesis , promoted by Evan P . Marshall , is based on statistical analysis of actual shooting incidents from various reporting sources ( typically police agencies ) . It is intended to be used as a unit of measurement and not as a tactical philosophy , as mistakenly believed by some . It considers the history of shooting incidents for a given factory ammunition load , and compiles the percentage of " one - shot - stops " achieved with each specific ammunition load . That percentage is then intended to be used with other information to help predict the effectiveness of that load getting a " one - shot - stop . " For example , if an ammunition load is used in 10 torso shootings , incapacitating all but two with one shot , the " one - shot - stop " percentage for the total sample would be 80 % . Some argue that this hypothesis ignores any inherent selection bias . For example , high - velocity 9 mm hollow point 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 predominantly used 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 . However , Marshall ' s database of " one - shot - stops " does include shootings from law enforcement agencies , private citizens , and criminals alike . Critics of this theory point out that bullet placement is a very significant factor , but is only generally used in such one - shot - stop calculations , covering shots to the torso . Since 2006 , after the conviction of retired school teacher Harold Fish in Arizona for second degree murder during a self - defense shooting , some CCW holders in the United States have elected to switch from carrying hollow - point bullets , and especially 10mm Auto caliber weapons with perceived higher one - shot stopping power , to carrying smaller caliber weapons . Fish ' s conviction for killing a homeless man with a history of dangerous violent behavior and mental instability who attacked Fish while hiking on a remote trail , was obtained through a jury trial by stressing that Fish overreacted , through choosing to use the increased stopping power of 10 mm hollow point bullets . State law in Arizona has subsequently been changed , such that the state now has the burden to prove that a self - defense shooting was not in self - defense , whereas the burden previously , before the Fish incident , was that the shooter on trial had to prove that the shooting was in fact , done in self - defense . The conviction has since been thrown out by the Arizona Court of Appeals . CCW training classes often advise the use of bullets that are identical to those used by local police , in type ( FMJ or hollow point ) and caliber , to prevent an overreaction prosecution . Big Hole School . This school of thought says that the bigger the hole in the target the higher the rate of bleed - out and thus the higher the rate of the aforementioned " one shot stop " . According to this theory , as the bullet does not pass entirely through the body , it incorporates the energy transfer and the overpenetration ideals . Those that support this theory cite the . 40 S & W round , arguing that it has a better ballistic profile than the . 45 , and more stopping power than a 9×19mm Parabellum . The theory centers on the " permanent cavitation " element of a handgun wound . A big hole damages more tissue . It is therefore valid to a point , but penetration is also important , as a large bullet that does not penetrate will be less likely to strike vital blood vessels and blood - carrying organs such as the heart and liver , while a smaller bullet that penetrates deep enough to strike these organs or vessels will cause faster bleed - out through a smaller hole . The ideal may therefore be a combination ; a large bullet that penetrates deeply , which can be achieved with a larger , slower non - expanding bullet , or a smaller , faster expanding bullet such as a hollow point . In the extreme a heavier bullet ( which preserves momentum greater than a lighter bullet of the same caliber ) may " overpenetrate " , passing completely through the target without expending all of its kinetic energy . So - called " overpenetration " is not an important consideration when it comes to wounding incapacitation or " stopping power " , because : ( a ) while a lower " proportion " of the bullet ' s energy is transferred to the target a higher " absolute amount " of energy is shed than in partial penetration , and ( b ) overpenetration creates an exit wound . Other contributing factors . As mentioned earlier , there are many factors , such as drug and / or alcohol levels within the body , body mass index , mental illness , motivation levels , body part strike ( e . g . " armpit hold " ) which may determine which round will kill or at least catastrophically affect a target during any given situation .