A barrel assembly with a barrel is provided. The barrel comprises a plurality of external chambers containing respective propellant charges, a plurality of projectiles stacked nose to tail within the barrel and comprising respective expansion spaces for propellant gases, and a control system configured to ignite the propellant charges to create the propellant gases and propel the projectiles sequentially from the barrel. Each projectile has a corresponding external chamber and an expansion space and each chamber comprises a port that conveys propellant gas from the chamber into the expansion space for propulsion of the respective projectile.