Teflon - coated bullet Teflon - coated bullets , sometimes colloquially known as " cop killer bullets " , are bullets that have been covered with a coating of polytetrafluoroethylene . History . 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 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 Ordinance 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 cartridges , although the 9mm offering was reputed to push a 100grn projectile at a velocity of 1350fps . Controversy . In 1982 , NBC ran a television special on the bullets , supposedly against the requests of many police organizations , 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 vest s , 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 . A common resulting misconception , often perpetuated in film 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 . Several of the various calibers of KTW rounds produced could , in fact , penetrate police vests , under certain conditions . However , as Kopsch pointed out in a 1990 interview , " adding a Teflon coating to the round added 20 % penetration power on metal and glass . Critics kept complaining about Teflon ' s ability to penetrate body armor . . . In fact , Teflon cut down on the round ' s ability to cut through the nylon or Kevlar of body armor . " Legal status . United States . The federal ban on armor - piercing pistol ammunition uses only the composition of the bullet ' s core to determine legality . However , many individual states have legislation restricting various kinds of coating materials . For example :