iirc "cop killer" bullets were the Black Talons. I know of a few people that still have these, bought pre-ban of course. They were suppose to be able to penetrate kevlar bullet proof vest.
Just found this:
Wikipedia: The ammunition was targeted by those opposed to handguns,
and the reputation was very different in the public,
and eventually the Talons became to be known by the moniker "cop-killer" bullets.
The hype of the Black Talon ammunition was the black coating on the bullets themselves. There were false rumors that the bullets were armor piercing and could penetrate the Kevlar vests worn by police officers.