Abstract: A fin-stabilized projectile comprises a body section and a tail section disposed along a longitudinal axis. The tail section includes an outer end portion, a fin-carrying portion, and a boom portion having a tubular wall defining an ignition propellant gas chamber with a plurality of propellant gas ejection holes therein. An ignition cartridge load package includes a main propellant charge and an end cap firing section. The main propellant charge is disposed within the tubular boom portion and includes compacted particulate propellant material. The particulate propellant material forms a rigid, elongated wall structure defining open passageways for directing propellant igniting gases from the end cap firing section through the boom portion toward the body section. The open passageways direct propellant igniting gases from the end cap firing section along surfaces along the wall structure to ignite the propellant material forming the wall structure.

Abstract: A firearm having a smooth-bore barrel for firing fin-stabilized projectiles includes a muzzle assembly at the end of the barrel for stabilizing the projectile as it leaves the barrel upon being fired. The muzzle assembly includes a radial opening portion having apertures along the periphery of the assembly to exhaust firing gases therethrough. A gas guiding or diverting structure is mounted along the outside of the assembly and includes a deflection surface adjacent the apertures in the radial opening portion to divert any exhausted firing gases radially from the barrel and thereby prevent the exhausted firing gases from affecting the trajectory of the finned projectile. The aperture may be formed as slots in the barrel adjacent its end or provided between the end of the barrel and the gas guiding structure which is displaced laterally from the muzzle opening of the barrel along the longitudinal axis thereof.