U.S. civilians own an estimated 20 million AR-15s. How the rifle became a political symbol

The AR-15, a rifle designed for American soldiers, has grown in popularity among civilians. The authors of "American Gun: The True Story of the AR-15" trace the history of the rifle and how it became one of the most polarizing weapons in America.
In the 1950s, Eugene Stoner designed a light weight, rapid fire rifle. The AR-15 became the standard-issue weapon for military service members.

The weapon was once banned in America, but now an estimated 20 million are in civilian hands.

"And what's remarkable is that if you go back just to 1994, there were only 400,000 in the country at that time," said Zusha Elison, co-author of the book "American Gun: The True Story of the AR-15."

"There was this political battle and the AR-15 was suddenly turned into this, not just a firearm, but a political statement," co-author Cameron McWhirter said.

Elison and McWhirter trace the history of the weapon that has become emblematic of gun rights, how it grew in popularity and why it is an attractive rifle to mass shooters in America.