Teflon-coated bullet

Teflon-coated bullets, sometimes colloquially, but incorrectly known as "cop killer bullets", are bullets that have been covered with a coating of polytetrafluoroethylene.

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. The inventors named their company "KTW," after their initials.

After some experimentation with sintered tungsten-alloy rounds, which were eventually abandoned due to supply and cost concerns, the inventors settled on a bullet consisting mostly of hardened brass with a steel core. In testing, the comparatively hard brass bullets wore out barrels far more quickly than standard solid lead and copper-jacketed lead rounds, since they did not deform to fit the rifling. In an attempt to reduce barrel wear, the bullets were experimentally coated with a protective layer of Teflon. The inventors, having also noted that the tips of canes were frequently covered with the relatively soft and malleable Teflon to help them grip surfaces, found that the addition of Teflon helped to prevent bullet deflection off of vehicle doors and windshields, further improving penetration against those surfaces.

By the late 1960s, KTW had begun commercial production. In 1980, continued production of the ammunition was turned over to the North American Ordnance Corporation. The production of KTW-branded ammunition eventually ceased in the 1990s. However, some manufacturers continue to coat their bullets with various compounds, notably Teflon and molybdenum disulfide, as a protective layer against barrel wear.

Not a lot of performance data is available for these bullets, although the 9mm offering was reputed to push a 100grn projectile at a velocity of 1350fps.

In 1982, NBC ran a television special on the bullets, wherein it was argued that the bullets were a threat to police. Various gun control organizations in the U.S. labeled Teflon-coated bullets with the epithet "cop killers" because of the supposedly increased penetration the bullets offered against ballistic vests, a staple of the American police uniform. Many erroneously focused on the Teflon coating as the source of the bullets' supposedly increased penetration, rather than the hardness of the metals used and the sharp conical projectile form factor. Woven Ballistic Vests, like Kevlar, rely on the dense weave of the textile and the tensile strength of the fiber to create resistance(or drag) on the exterior of the projectile slowing and eventually stopping the bullet before it penetrates all of the fabric layers of a vest. The idea that Teflon coating would increase penetration was drawn from the fact that Teflon is a very good lubricant. The lubricant would retard the effectiveness of the Kevlar fabric to slow the bullet and "catch" it. A common resulting misconception, often perpetuated in film (e.g., Ronin (1998)) and television, is that coating otherwise normal bullets with Teflon will give them armor-piercing capabilities. In reality, as noted above, Teflon and similar coatings were used primarily as a means to protect the gun barrel from the hardened brass bullet, and, secondarily, to reduce ricochet against hard, angled surfaces. The coating itself did not add any armor-piercing abilities to bullets under normal circumstances.

...
Wikipedia