AR is the abbreviation and trademarked as such for the company that originally designed the thing, Armalite Co. which ironically, designed the weapon as a hunting rifle in .222 not .223 but when bidding for the military platform, they changed it to the more popular .223.
Number 2: Assault Rifles are already illegal to own without a special permit issued by the BATFE. And none have been made for the civilian market since 1986. Those rifles cost literally, 20-30 THOUSAND dollars a piece, require a 200 dollar permit, cannot be sold or traded with out BATFE background checks, which take upwards of 18-24 months.