This photo was taken using 100 speed film at f8, with the film plane about 13 inches from the bb.  Two wires connecting the batteries and the strobe were positioned so they would be forced together by the puff of air from the muzzle of the bb gun and cause the flash.  After everything was set up, the lights were turned out, the shutter was locked open using the bulb shutter speed and a cable release, the bb gun was fired, the shutter was closed, then the lights were turned back on.  In this way, only the burst of light from the strobe recorded an image on the film.