https://www.congress.gov/bill/101st-congress/senate-bill/386...

This was Metzenbaum's reaction to the Stockton massacre; it was covered in the NYT (both at the time and in retrospectives about how we ended up with our batty FAWB). Note that in addition to definitionally regulating AR-15s, it also bans them outright by name.

(The definitional criteria here is --- this is from a skim and from memory, so correct me but don't jump on me if I have this wrong --- any semi-automatic rifle with a detachable magazine that accepts more than 10 rounds).