FBI Annual Report of results of handgun ammunition testing. said:
After extensive research and consultation, the FBI established that a handgun bullet must consistently penetrate a minimum of 12 inches of tissue in order to reliably penetrate vital organs within the human target regardless of the angle of impact or intervening obstacles such as arms, clothing, glass, etc. Penetration of 18 inches is even better. Given minimum penetration, the only means of increasing wound effectiveness is to enlarge the permanent cavity. This increases the amount of vital tissues with a marginally placed shot, and increases the potential for quicker blood loss. This is important because, with the single exception of damaging the central nervous system, the ONLY way to force incapacitation upon an unwilling adversary is to cause enough blood loss to starve the brain of its oxygen and/or drop blood pressure to zero. This takes time, and the faster haemorrhage can occur the better.
The FBI ammunition test protocol is a series of practically oriented tests to measure a bullet's ability to meet these performance standards. The result is an assessment of a bullet's ability to inflict effective wounds after defeating various intervening obstacles commonly present in law enforcement shootings. The overall results of a test are thus indicative of that specific cartridge's suitability for the wide range of conditions in which law enforcement officers engage in shootings.
The test media used by the FBI to simulate living tissue is 10% ballistic gelatin (Kind & Knox 250-A), mixed by weight. The gelatin is stored at 4x Centigrade (39.2x Fahrenheit) and shot within 20 minutes of being removed from the refrigerator. The temperature of the gelatin is critical, because penetration changes significantly with temperature. This specific gelatin mix was determined and calibrated by the U.S. Army Wound Ballistics Research Laboratory, Presidio of San Francisco, to produce the same penetration results as that obtained in actual living tissue. Each gelatin block is calibrated before use to ensure its composition is within defined parameters. The gelatin blocks for handgun rounds are approximately six inches square and 16 inches long. As necessary, additional blocks are lined up in contact with each other to ensure containment of the bullet's penetration. Each shot's penetration is measured to the nearest 0.25 inch. The projectile is recovered, weighed and measured for expansion by averaging its greatest diameter with its smallest diameter.
The ammunition test protocol using this gelatin is composed of eight test events. In each test event, five shots are fired. A new gelatin block and new test materials are used for each individual shot. The complete test consists of firing 40 shots. Each test event is discussed below in order.
All firing in these eight test events is done with a typical service weapon representative of those used by law enforcement. The weapon used is fully described in each test report.
Test Event l--Bare Gelatin
The gelatin block is bare and shot at a range of ten feet measured from the muzzle to the front of the block. This test event correlates FBI results with those being obtained by other researchers, few of whom shoot into anything other than bare gelatin. It is common to obtain the greatest bullet expansion in this test. Rounds which do not meet the standards against bare
gelatin tend to be unreliable in the more practical test events that follow.
Test Event 2--Heavy Clothing
The gelatin block is covered with four layers of clothing: One layer of cotton T-Shirt material (48 threads per inch); one layer of cotton shirt material (80 threads per inch); a I0 ounce down comforter in cambric shell cover (232 threads per inch); and one layer of 13 ounce cotton denim (50 threads per inch). This simulates typical cold weather wear. The block is shot at ten feet, measured from the muzzle to the front of the block.
Test Event 3—Steel
Two pieces of 20 gauge, hot rolled steel with a galvanised finish are set three inches apart. The steel is in six inch squares. The gelatin block is covered with light clothing and placed 18 inches behind the rear most piece of steel. The shot is made at a distance of I0 feet measured from the muzzle to the front of the first piece of steel. Light clothing is one layer of cotton T-Shirt material and one layer of cotton shirt material, and is used in all subsequent test events. The steel is the heaviest gauge steel commonly found in automobile doors. This test simulates the weakest part of a car door. In all car doors, there is an area, or areas, where the heaviest obstacle is nothing more than two pieces of 20 gauge steel.