In recent years, the AR-15 has become, simultaneously, one of most beloved and most vilified rifles in the country. It is no surprise why the gun is so reviled by gun control advocates. Omar Mateen, the gunman in the attack this weekend on a gay nightclub in Orlando, Fla., used a spinoff of the rifle produced by SIG Sauer to kill nearly 50 people. The military-style weapon has also been the gun of choice in several other mass shootings: at an elementary school in... (GunPolicy.org)