AR vs M-16

AR

noun

  • an assault rifle or automatic rifle. 

  • area record: best achievement among those by persons from a given continent 

  • an AR-15 personal semi-automatic rifle, M-16 assault rifle, M-4 carbine, derivative or related gun; the Armalite AR family and derivatives. 

  • alternate reality 

name

  • Postal abbreviation of Arkansas 

M-16

noun

  • A lightweight assault rifle, originating from the Vietnam War period 

How often have the words AR and M-16 occurred in a corpus of books? (source: Google Ngram Viewer )