US Patent 11933592 Ammunition casing having a cannelure with step

A casing for an ammunition cartridge comprises a sleeve portion and a base portion. The casing may be two-piece, where the base portion is secured to the sleeve portion by means of a nipple having a flared end. The base portion comprises a cannelure that extends lengthwise from a flange. The cannelure, which is preferably curved, is deeper than a conventional cannelure and thus the casing weight is reduced. The cannelure has a step that is adjacent the flange, for limiting inward travel of the lip of a hook of the bolt of a firearm. Alternatively, a casing may be a one-piece casing, wherein the base and sleeve are integral.