Slugs are commonly fired from choked smoothbore barrels, but some specially-designed slug barrels have riflings that can impart gyroscopic spin required for in-flight stability.
type of pellet recently developed for pre-charged pneumatic airguns.
Unlike the conventional diabolo-shaped pellet, which is aerodynamically poor and relies heavily on drag-stabilisation to maintain accuracy, the slug pellet is cylindro-conoidally shaped like a Minié ball and relies predominantly on spin-stabilisation from a rifled barrel.
Because of the greater contact area with the barrel bore, these pellets require more power from the gun to overcome the frictional resistance, and therefore are mainly used in PCP airguns, which generally have much higher muzzle energy ratings than other types of airguns such as spring-piston, pump pneumatic or HPA/CO2 airguns.
In simulated naval battles and exercises this is to represent the dispatch of an actual torpedo as, to sonar detectors, the sounds are very alike.