It was a shot heard 'round the world. In early May, you could sit in front of a computer in Manhattan or Moscow or New Delhi and watch a 53-second video. In it, a young man stands purposefully among hilly scrub, holding a weird-looking white toy. Then he fires it, just once. He turns and looks at the camera, defiant. Brian Doherty describes the two days he spent with Cody Wilson, the inventor of a 3D printed gun called "the Liberator."