US Patent 8408137 Spiral case ammunition

A cartridge for a firearm comprises a case having a base located at one end and a projectile mounted at the other end. A specific volume of propellant is contained in the case and is ignitable via a primer located in the base. The ignition of the propellant causes the projectile to be propelled from the case. The case comprises a wall defining a plurality of circumferential flutes that extend around outer and inner surfaces of the case in a helical or vertical configuration.