At last count, there are ~400 million privately owned firearms in this country. I'll wager that 1/4 of that number are AR15s, the most popular rifle in America.
Until they stop the distribution of ammo (inc. powder, primers, brass) w/o ammo, 400 million guns are no better than 400. Federal goons can shut down the industry or take it over. It will have to be all underground.