Bourrelet

The bourrelet is the portion of an elongated artillery projectile having a very slightly smaller diameter than the interior diameter of the barrel through which that projectile is to be propelled. The bourrelet is typically precisely machined to a specified diameter after the remainder of the cast projectile body has been roughly machined to a smaller diameter. The bourrelet is normally forward of a rotating band or driving band near the aft end of the projectile. The rotating or driving band is customarily made of a softer metal than the remainder of the artillery projectile and of a larger diameter than the bourrelet to seal the barrel and be engraved by the rifling to spin-stabilize the projectile in flight. The bourrelet is not engraved by the rifling, but is supported by the lands between the rifling to align the long axis of the projectile with the axis of the artillery bore.