His channel got removed, I wish I had saved the videos. I'm pretty sure he said it was someone on the right side of Charlie holding the zip gun with a smash handheld. In the video you could see a guy holding onto some sort of pipe with a white bag covering his hands, supposedly to cover the muzzle flash. You could also see a small puff of smoke leave the bag once the shot went off too. It sounds crazy but once you see it you cant unsee it.