To impart a longitudinal spin to a projectile which gives gyroscopic stability to the projectile which greatly increases its accuracy.

The plane in which the reactive gyroscipic couple acts is called the gyroscopic plane

principle of gyroscopic couple ?

how gyroscopic coule work in a aroplanes & ship ?

If the precessionnal motion is caused by applying gravitational torque,it is called

gyroscopic motion.

This is a shallow spiral groove cut into the inside of a gun's barrel. As a gun shoots, the projectile engages these grooves and they impart a longitudinal spin to the bullet. This creates gyroscopic stability which greatly increased the accuracy of the projectile.