Abstract: A housing (1; 100, 104, 102) of a cartridge for a device for firing a projectile has separate first and second chambers (10, 12; 106, 114), each of which contains a respective charge (34, 36; 108, 110, 116, 120) of propellant material. Gas produced by the detonation of one of the charges exits the first chamber to propel the projectile, whilst gas from the detonation of the second charge exist rearwardly from the device so as to counteract recoil. A one way valve may also be provided to help to achieve a high pressure difference between the chambers, where the cartridge has a common igniter assembly.