Teflon-coated bullets are handgun bullets that have been covered with a coating of Teflon to reduce barrel wear. Molybdenum disulfide is also sometimes used as a coating.
In the 1960s, Paul Kopsch (an Ohio coroner), Daniel Turcos (a police sergeant), and Donald Ward (Kopsch's special investigator), began experimenting with special purpose handgun ammunition. Their objective was to develop a law enforcement round capable of improved penetration against hard targets, such as windshield glass and automobile doors. Conventional bullets, made primarily from lead, often become deformed and less effective after striking hard targets, especially when fired at handgun velocities.
After some experimentation with steel rounds, the officers settled on a brass core. Unlike lead, which is relatively malleable, brass wore out barrels far more quickly than normal jacketed rounds, since the brass did not reform to fit the rifling. For this reason, the bullets were then coated with a layer of Teflon to reduce barrel wear. The inventors named the round the "KTW Bullet," after their initials. Capable of penetrating car doors and windshields, the new rounds also offered increased penetration of some types of bullet proof vest|bullet-resistant vests.
In 1982, NBC ran a special on the bullets and argued that the bullets were a threat to police. Gun politics in the United States|Gun control organizations in the U.S. labeled Teflon-coated bullets "cop killers" because of the supposedly increased penetration the bullets offered against bullet proof vests, a staple of the American police uniform. Many people believed that the Teflon coating was responsible for this increased penetration despite the fact that the material is only a outter coating for the brass penetrator and usually peels off during its trajectory through the air. Ultimately, there is no evidence that Teflon-coated rounds penetrate bullet proof vests more easily than standard bullets.
No law enforcement personnel has yet been killed by this type of round when wearing appropriate body armor, making the nickname "cop killer" misleading.
The federal ban on armor-piercing ammunition uses only the composition of the bullet's core to determine legality. However, many states have legislation restricting various kinds of coating materials. For example, South Carolina state law specifically bans "ammunition or shells that are coated with polytetrafluoroethylene (Teflon)" (SC Code 16-23-520).