You'd have to ask the retards who coined that phrase.
Hollow points inflict more internal tissue damage than FMJs but I don't know how that relates to bullet proof vests and "cop killing".
Hollow points would have less of a chance of going thru a bullet proof vest than Full metal jacket conical rounds would have.
The Winchester 30-30 round is the actual "cop killer" round, and it is fired from a rifle 90 percent of the time. It is not an autoloading round and normally shot from a lever action rifle. It ballistically goes thru pretty much anything, but is a deer hunting round.
Some more anti nomenclature bs.