"Parkland, Florida. Las Vegas, Nevada. Sutherland Springs, Texas. Now, Pittsburgh, Pennsylvania. Recent deadly mass shootings in these US cities have at least one thing in common: the AR-15.... This weapon has become increasingly popular in the US, especially since the 1994 federal weapons ban expired in 2004, and has been used in many other mass shootings around the country. Not just the three listed above. To understand how and why this has happened, we put together a historical overview of the weapon and spoke with David Chipman, a senior policy analyst at Giffords and former special agent with the Bureau of Alcohol, Tobacco, Firearms, and Explosives.... Chipman said that he believes AR-15s have been so frequently used in mass shootings for two reasons: popularity and lethality. "It's a two-fold thing: the AR-15 is like the 4-door sedan of assault rifles," Chipman said. "It was America's weapon ... there's an Americana aspect." But so many mass shootings become mass shootings "because the AR-15 was used," he said, adding that the damage the weapon does to the human body pales in comparison to a handgun. "I've talked to ER physicians," Chipman said. "Rifle rounds are so devastating to the human body.""