This is a photo of an M1A1 Abrams tank during gunnery training at the Grafenwohr Training Area in West Germany in 1987. The horizontal line leading to the right from the firing tank is the tracer from the main gun round on its way to the target. The wavy lines coming off of the main tracer are from the sabot petals coming off of the bullet. The sabots are attached to the bullet's penetrator during its trip through the gun tube and they fall off once the bullet leaves the tube. They exist because a larger gun diameter allows for a higher bullet velocity in the tube, but once in the air, a long, thin rod flies and kills targets better than a wider, shorter one.