Aluminum cartridge case

Abstract

An improved cartridge case is fabricated from rod or bar stock formed from a billet of an alloy containing, by weight, 5.2 to 6.2% Zn, 1.9 to 2.5% Mg, 1.2 to 1.9% Cu, 0.18 to 0.25% Cr, the remainder essentially aluminum. The method of fabrication of the cartridge case from a billet of the alloy comprises a controlled sequence of steps in forming rod or bar working stock so as to ensure against the formation of coarse recrystallized grains and the consequent forming of surface cracks or checks in subsequent metal working operations which include segmenting the rod, annealing the segmented parts and thereafter forming such segments into cartridge cases by cupping and wall ironing procedures. The mouth of the case can be annealed for ease of forming a retaining groove about a projectile positioned in the mouth of the case and in some instances for providing resistance to stress corrosion cracking.