Abstract: Cartridge ammunition (10) including a projectile (12) and a cartridge case (14). The cartridge includes a primer chamber (26) located adjacent a base wall (24) for holding a primer (28), a high pressure chamber (30) for holding a propellant charge (32), an intermediate pressure chamber (34) which surrounds the high pressure chamber, for receiving expanding propellant gases from the high pressure chamber and a low pressure chamber (36) at a rear end of the projectile for receiving expanding propellant gases from the intermediate pressure chamber. The pressure chambers are delimited by walls defining venting hole through which expanding gases can flow. The three pressure chambers provide for controlled release of gas pressure resulting in attenuation of peak gas pressures within the cartridge.