I'm only familiar with the old KTW green Teflon coated stuff.
When the KTW ammunition was first put on the market in the late 1960’s, anyone could purchase it. But, it soon become known as “cop killer ammo” as they would easily penetrate bullet proof vests. This was unwarranted as, according to the FBI, no police had ever been killed by anyone using this ammunition. But, because of the misconception, it was soon available only to the police. It was removed from the market in the 1990’s.
The bullets were at first made from a type of bronze called Kennertium (non-magnetic) covered with green Teflon. Later they changed to steel (magnetic) covered with Teflon as it worked just as good and was much less expensive to make.
The KTW stands for Kopsch, Turcus and Ward, the three inventors of the bullet. The early rounds were headstamped “KTW” but later production used mostly Winchester cases, but can also be found in Remington, Smith & Wesson and other cases.
It was made in all major handgun calibers from .25 Auto to .45 ACP.
9mm KTW shown below.