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One of the guns used to kill 14 people in San Bernardino, CA this past week has also been used in mass shooting after mass shooting in recent years.

The AR-15—a semi-automatic rifle that one of its makers, Colt, describes as being produced for "our Armed Forces"—has played an outsized role in America's gun massacres, as CBS News summarized on Friday:

An AR-15 was used to kill nine people at Umpqua Community College in Oregon in October.

It was also the weapon used in the murders of 12 people at a Colorado movie theater in 2012.

And an AR-15 was used in the 2012 murders of 20 first graders and six adults in Newtown, Connecticut.

CBS spoke to a gun store owner who called the AR-15 "America's rifle" and added, "You're going to find more of those in safes at home than you'll find of any other rifle in the country."

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Sales of the AR-15 spiked after the Newtown shootings, as potential gun owners feared—wrongly, it turned out—that they might be subject to new gun control restrictions. Though the market has cooled off a bit recently. They're popular because, as CNN noted, they can be customized in a dizzying number of ways. One manufacturer gives purchasers at least 17 different ways to build on its basic model.

As it happens, the AR-15s used in the San Bernardino shooting was illegal under California law because of the way it had been customized.

Some forms of the AR-15 were banned under the 1994 Federal Assault Weapons Ban, but the ban expired in 2004.