A barrel assembly (70) comprising a plurality of projectiles (75) axially disposed within a barrel (71) and associated with discrete selectively ignitable propellant charges (74) for propelling the projectiles from the barrel. The essence of the invention is the provision of a pressure relief valve, for example comprised by a port (73) and plug (76), associated with a chamber in which a propellant charge (74) is ignited. The pressure relief valve (73, 76) is designed to prevent catastrophic failure of the barrel (71) by exhausting via a chamber (72) in the event that the barrel is blocked by a projectile and detonation of one or more propellant charges (74) occurs.