in flight from the rifling of the gun barrel, which imparts a spin to the round. Up to a certain limit, this is effective, but once the projectile's length is more than six or seven times its diameter, the gyroscopic effect imparted by barrel rifling becomes less effective. Adding fins to the base of the round like the fletching of an arrow instead gives the round its stability in flight.

The spin from standard rifling decreases the performance of these rounds (rifling adds friction and converts some