Tracer ammunition

Illuminated pyrotechnic ammunition visible in daylight and darkness

Tracer ammunition, or tracers, are bullets or cannon-caliber projectiles that are built with a small pyrotechnic charge in their base. When fired, the pyrotechnic composition is ignited by the burning powder and burns very brightly, making the projectile trajectory visible to the naked eye during daylight, and very bright during nighttime firing. This allows the shooter to visually trace the trajectory of the projectile and thus make necessary ballistic corrections, without having to confirm projectile impacts and without even using the sights of the weapon.

From Wikipedia, under CC BY-SA. More on occurri.