"The gunman charged with killing 17 people at a Florida high school on Wednesday used an AR-15 model rifle, a style of gun that has become more commonly used in mass shootings in the past decade. The AR-15 is a semiautomatic rifle that allows the user to fire rapidly and use high-capacity magazines. Four out of the five deadliest mass shooting in modern U.S. history have taken place since 2012 and all four of those shooters used AR-15 model rifles in their attacks, including Stephen Paddock in Las Vegas and Adam Lanza in Newtown, Conn. The AR-15 model rifle is among the most popular firearms today, according to the National Shooting Sports Foundation, the firearms industry trade association. Gun owners like them because they are easily customized and can be used for hunting or target practice, according to the association. Some Democratic lawmakers and gun-control groups want to ban or restrict AR-15 model guns, calling them weapons of war."