It has been called the most popular rifle in America, and it's back in the spotlight after Monday's shooting at the Navy Yard: The AR-15. Authorities said when Aaron Alexis unleashed a barrage of bullets Monday, he was carrying a rifle and a handgun. But he did most of the shooting with the weapon used in so many other rampages that shocked the nation: - Sandy Hook: Adam Lanza killed 26 people at the Sandy Hook elementary school in Newtown, Connecticut, with the AR-15... (GunPolicy.org)