1. A groove in a bullet which contains a lubricant, or into which the cartridge is crimped.

2. A groove in a cartridge case providing a purchase for the extractor.

3. A ringlike groove for locking the jacket of an armor-piercing bullet to the core.

4. A ringlike groove in the rotating band of a gun projectile to lessen the resistance offered to the gun rifling and to prevent fringing grooves.