Ammunition casing having a cannelure with step

Abstract

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.

What is claimed is: 
     
         1 . A casing for ammunition used in a firearm, the casing having a lengthwise centerline, a proximal end having a recess shaped for receiving a primer, and an opposing distal end comprising a mouth for receiving and holding a projectile, the casing comprising:
 a sleeve portion, for holding a quantity of gunpowder, the sleeve portion having a distal end characterized by the mouth, and an opposing proximal end from which runs lengthwise a cylindrical exterior surface having an associated diameter;   a base, having a distal end characterized by a cylindrical portion that is securely mated with or integral with the proximal end of sleeve portion, a proximal end characterized by a flange having a first side annular flange surface that forms at least a portion of the casing proximal end and an opposing second side annular flange surface that faces toward the distal end, the base further characterized by a cannelure situated between the flange and the distal end of the base, the cannelure characterized by a first cannelure surface portion that faces distally and comprises at least a portion of the second side annular flange surface; and   a second cannelure surface portion that is either contiguous with the first cannelure surface portion or spaced apart therefrom by a groove, the second cannelure surface portion extending lengthwise as a step having a diameter which is less than the diameter of the flange.   
     
     
         2 . The case of  claim 1 , further comprising
 a third cannelure surface portion, running inwardly from the second cannelure surface portion toward the casing centerline along a plane or a curve, and then extending lengthwise cylindrically or curvingly, and   a fourth cannelure surface portion, running outwardly from the third cannelure surface portion and away from the casing lengthwise centerline, the surface portion having either a conical or curved shape.   
     
     
         3 . The casing of  claim 2 , wherein the third cannelure surface portion runs inwardly toward the casing centerline along a curve and then extends curvingly lengthwise. 
     
     
         4 . The casing of  claim 2 , wherein the third cannelure surface portion runs inwardly toward the casing centerline along a curve and then extends curvingly lengthwise, and wherein the fourth cannelure surface portion runs curvingly outwardly with respect to the lengthwise centerline. 
     
     
         5 . The casing of  claim 2 , wherein a cannelure third surface portion runs cylindrically lengthwise; and wherein a fourth cannelure surface portion runs conically outwardly with respect to the centerline of the base. 
     
     
         6 . The casing of  claim 1 , wherein the sleeve portion and base are integral with each other. 
     
     
         7 . The casing of  claim 1 , wherein the base and the sleeve portion are separate components that are connected to each other. 
     
     
         8 . The casing of  claim 1  wherein the base has a central lengthwise passageway, and wherein the sleeve portion comprises a nipple positioned within the passageway, wherein the nipple tip is flared against a shoulder within the passageway to hold the base and the sleeve portion together. 
     
     
         9 . The casing of  claim 1  in combination with a projectile positioned in the mouth, a quantity of gunpowder disposed within the sleeve portion, and a primer cap disposed within the bore of the base, thereby forming a cartridge; and in further combination with a bolt of a firearm, the bolt having a hook, wherein the proximal end of the flange is in contact with the bolt, and wherein the hook has a lip positioned to pull on the flange first surface when the bolt moves in a direction away from the flange; and wherein the lip of the hook rests on the step of the flange.