311 days, 307 mass shootings in the U.S. (Source usatoday.com) When the thunder of gunfire broke through a country music dance hall packed with young people kicking back on “college night,” Thousand Oaks, California, added its name to a dark roster: the site of the 307th mass shooting. It took place on the 311th day of the year. A mass shooting is defined as four or more people shot. At Borderline Bar and Grill, 12 people were killed late Wednesday by a tall, hooded man dressed in black and covering his face with a bandana. Among those killed was Sheriff Sgt. Ron Helus, 54, who “died a hero” after he entered the bar and exchanged gunfire with the suspect.