tracer mixture[′trā·sər ‚miks·chər]
a pyrotechnic composition that makes visible the trajectory of rapidly moving objects, such as bullets or shells.
Tracer mixtures may produce fire or smoke; the first type is more common. Mixtures that produce fire usually include a fuel such as magnesium, a metal nitrate oxidizer, and an organic binder, such as an artificial resin. For small-caliber bullets (up to 5.62 mm), tracer mixtures that contain zirconium, KC104, and polyvinyl acetate are also used. Tracer mixtures burn at a rate of a few millimeters per second, producing a bright (thousands of candlepower) white or red flame.