Machine guns, which fire multiple shots with one pull of the trigger, have been technically illegal since the mid-1980s. Yet while some of the guns that Stephen Paddock used to shoot more than 500 people in Las Vegas had been modified to fire as automatic weapons, they were perfectly legal, according to rules established by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).

The modifications he appears to have made to his semi-automatic AR-15s, which by one estimate allowed him to fire as many as nine rounds per second, can be bought in many different forms on the internet. And fully automatic machine guns are still being sold from ads in the back pages of gun magazines.

Also high capacity mqgazines holding over 15 rounds.