Abstract: Expendable case ammunition of the type which is expelled as a unit through the barrel of a firearm and whose case separates from contained projectiles in flight, comprises a body and a cap, and may include a separate projectile container. These parts are made of a deformable material such as plastic, and are snap-locked together. The body has an interior transverse wall separating a projectile chamber from a propellant chamber, which is enclosed by the imperforate cap to permit the use of loose propellant and to protect against contamination and accidental ignition. An anvil is integrally formed in the propellant chamber wall to cooperate with an internal primer and a firing pin which penetrates the cap. A diaphragm region of the cap is ruptured by initiation of the primer, and the cap remains attached to the body during ignition of the propellant and travel of the ammunition unit through the barrel of the firearm.