Complete US Patent details on how to create fin–stabilized ammunition.

From the Abstract:

Tracer visibility of APFSDS projectiles can be enhanced through a combination of increased steady spin rate, reduced muzzle obscuration, and optimized airflow over the stabilizing fin geometry of the sub–projectile.

The preferred means to increase steady spin rates of the sub–projectile is to incline or deflect the fin blade tip portion, creating a larger, hotter burning, tracer plume.