AR vs AR-15

AR

noun

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

  • an assault rifle or automatic rifle. 

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

  • alternate reality 

name

  • Postal abbreviation of Arkansas 

AR-15

noun

  • A lightweight, semi-automatic rifle, based on the original design of the ArmaLite AR-15. 

How often have the words AR and AR-15 occurred in a corpus of books? (source: Google Ngram Viewer )