So, how did he do it? With a very precisely timed flash and camera synchronization. They clamped a gun in place, and fired tens of shots at a specific target. For each shot, the flash and camera fired a little bit later in the process. These images were then stitched together to create a slow motion effect, as the bullet moves through the air. Yup, it's just like stop-motion animation, but using objects actually moving rather than carefully placed and positioned.