The Bump Stock

A bump stock device, approved by President Obama’s ATF in 2010, was allegedly used by the Las Vegas shooter at Mandalay Bay.

The bump stock can often jam and produces inaccurate fire, prompting an ATF official in 2010 to describe it as ““… a goofy, little doodad.”

Read more at Breitbart

UPDATE: Bump stocks can be 3D printed (Washington Examiner story)