This is from the FBI on many issues associated with handgun shootings (from a LEO perspective). It is quite fascinating.
Because of the length of the article this will be separated into 6 posts.
U.S. Department of Justice
Handgun Wounding Factors and Effectiveness
Special Agent UREY W. PATRICK
FIREARMS TRAINING UNIT
July 14, 1989
The selection of effective handgun ammunition for law enforcement is a critical and complex issue. It is critical because of that which is at stake when an officer is required to use his handgun to protect his own life or that of another. It is complex because of the target, a human being, is amazingly endurable and capable of sustaining phenomenal punishment while persisting in a determined course of action. The issue is made even more complex by the dearth of credible research and the wealth of uninformed opinion regarding what is commonly referred to as "stopping power".
In reality, few people have conducted relevant research in this area, and fewer still have produced credible information that is useful for law enforcement agencies in making informed decisions.
This article brings together what is believed to be the most credible information regarding wound ballistics. It cuts through the haze and confusion, and provides common-sense, scientifically supportable, principles by which the effectiveness of law enforcement ammunition may be measured. It is written clearly and concisely. The content is credible and practical. The information contained in this article is not offered as the final word on wound ballistics. It is, however, an important contribution to what should be an ongoing discussion of this most important of issues.
John C. Hall
Firearms Training Unit
The handgun is the primary weapon in law enforcement. It is the one weapon any officer or agent can be expected to have available whenever needed. Its purpose is to apply deadly force to not only protect the life of the officer and the lives of others, but to prevent serious physical harm to them as well.1 When an officer shoots a subject, it is done with the explicit intention of immediately incapacitating that subject in order to stop whatever threat to life or physical safety is posed by the subject. Immediate incapacitation is defined as the sudden2 physical or mental inability to pose any further risk or injury to others.
The concept of immediate incapacitation is the only goal of any law enforcement shooting and is the underlying rationale for decisions regarding weapons, ammunition, calibers and training. While this concept is subject to conflicting theories, widely held misconceptions, and varied opinions generally distorted by personal experiences, it is critical to the analysis and selection of weapons, ammunition and calibers for use by law enforcement officers.3,4
Shot placement is an important, and often cited, consideration regarding the suitability of weapons and ammunition. However, considerations of caliber are equally important and cannot be ignored. For example, a bullet through the central nervous system with any caliber of ammunition is likely to be immediately incapacitating.5 Even a .22 rimfire penetrating the brain will cause immediate incapacitation in most cases. Obviously, this does not mean the law enforcement agency should issue .22 rimfires and train for head shots as the primary target. The realities of shooting incidents prohibit such a solution.
Few, if any, shooting incidents will present the officer with an opportunity to take a careful, precisely aimed shot at the subject’s head. Rather, shootings are characterized by their sudden, unexpected occurrence; by rapid and unpredictable movement of both officer and adversary; by limited and partial target opportunities; by poor light and unforeseen obstacles; and by the life or death stress of sudden, close, personal violence. Training is quite properly oriented towards "center of mass" shooting. That is to say, the officer is trained to shoot at the center of whatever is presented for a target. Proper shot placement is a hit in the center of that part of the adversary which is presented, regardless of anatomy or angle.
A review of law enforcement shootings clearly suggests that regardless of the number of rounds fired in a shooting, most of the time only one or two solid torso hits on the adversary can be expected. This expectation is realistic because of the nature of shooting incidents and the extreme difficulty of shooting a handgun with precision under such dire conditions. The probability of multiple hits with a handgun is not high. Experienced officers implicitly recognize that fact, and when potential violence is reasonably anticipated, their preparations are characterized by obtaining as many shoulder weapons as possible. Since most shootings are not anticipated, the officer involved cannot be prepared in advance with heavier armament. As a corollary tactical principle, no law enforcement officer should ever plan to meet an expected attack armed only with a handgun.
The handgun is the primary weapon for defense against unexpected attack. Nevertheless, a majority of shootings occur in manners and circumstances in which the officer either does not have any other weapon available, or cannot get to it. The handgun must be relied upon, and must prevail. Given the idea that one or two torso hits can be reasonably expected in a handgun shooting incident, the ammunition used must maximize the likelihood of immediate incapacitation.
Mechanics of Projectile Wounding
In order to predict the likelihood of incapacitation with any handgun round, an understanding of the mechanics of wounding is necessary. There are four components of projectile wounding.6 Not all of these components relate to incapacitation, but each of them must be considered. They are:
(1) Penetration. The tissue through which the projectile passes, and which it disrupts or destroys.
(2) Permanent Cavity. The volume of space once occupied by tissue that has been destroyed by the passage of the projectile. This is a function of penetration and the frontal area of the projectile. Quite simply, it is the hole left by the passage of the bullet.
(3) Temporary Cavity. The expansion of the permanent cavity by stretching due to the transfer of kinetic energy during the projectile’s passage.
(4) Fragmentation. Projectile pieces or secondary fragments of bone which are impelled outward from the permanent cavity and may sever muscle tissues, blood vessels, etc., apart from the permanent cavity.7,8 Fragmentation is not necessarily present in every projectile wound. It may, or may not, occur and can be considered a secondary effect.9
Projectiles incapacitate by damaging or destroying the central nervous system, or by causing lethal blood loss. To the extent the wound components cause or increase the effects of these two mechanisms, the likelihood of incapacitation increases. Because of the impracticality of training for head shots, this examination of handgun wounding relative to law enforcement use is focused upon torso wounds and the probable results.