Advantages of the 9mm pistol include its lighter weight, greater capacity and quick reloading, moderate recoil, and suitability for both on- and off-duty use. In 1987, the Federal Bureau of Investigation began a series of tests of 9mm semi-automatic handguns and various types of ammunition. In evaluating the likelihood of incapacitation with a handgun round, it is necessary to consider the components of projectile wounds. These include penetration, the temporary and permanent cavities made by the projectile, and fragmentation of the projectile and/or bone. Recent studies have shown that to be effective as a manstopper, ammunition should cause deep penetration combined with a fairly large permanent cavity. Tests have shown that a bullet must reliably penetrate 10 to 12 inches of soft body tissue to maximize tissue damage and cause massive hemorrhaging. Tests also show that slow-moving, heavy bullets, particularly used in a 9mm pistol, produce better penetration and a good-sized cavity. While these tests indicate that the .38 special revolver is no match for the 9mm pistol, results also suggest that no caliber handgun can produce instant incapacitation with one shot unless it is a brain shot. Consequently police training should emphasize bullet placement and continuous fire until the adversary is down. Photographs.