Florida Rep. Alan Grayson used the aftermath of Sunday’s Islamic terror attack to claim AR-15 semi-automatic rifles can fire 700 rounds per minute. Security guard Omar Mateen killed 49 people and wounded over 50 others during an attack on a gay nightclub — the worst mass shooting in U.S. history. Mr. Grayson, a Democrat, was asked about the massacre and soon turned his attention to the AR-15 rifle. ... “If [Mr. Mateen] was not able to buy a weapon that shoots off 700 rounds in a minute, a lot of those people would still be alive,” the congressman said. “If...