Reduced tension cartridge case with two-stage neck

Abstract

Devices and methods for reducing tension force on a projectile by a neck of a cartridge case. A two-stage neck has a clearance band and an interference band, the clearance band providing a reduced retention force on the projectile relative to the interference band.

What is claimed is: 
     
         1 . A cartridge for a firearm, comprising:
 a projectile; and   a case, comprising:
 a base configured to hold a primer, 
 a body extending from a first end adjacent the base to a second end, and 
 a two-stage neck extending from the second end of the body to a mouth and configured to retain the projectile, the two-stage neck comprising a neck length, an interior surface, and an exterior surface, the interior surface of the two-stage neck comprising:
 an interference band comprising an interference diameter and extending an interference length along the two-stage neck, the interference band configured to provide an interference fit with the projectile resulting in an interference retention force, 
 a clearance band comprising a clearance diameter and extending a clearance length along the two-stage neck, and 
 a transition portion located between and adjoining the interference band and the clearance band, the transition portion comprising a continuous interior surface extending axially between the interference band and the clearance band, 
 wherein both the interference band and the clearance band are at least partially coextensive with the projectile when the projectile is seated in the case. 
 
   
     
     
         2 . The cartridge of  claim 1 , wherein an exterior of the two-stage neck comprises a reduced diameter relative to the body, the case further comprising a shoulder extending from the second end of the body to the two-stage neck, wherein the interference band extends from the shoulder to the clearance band, and the shoulder has a thickness that does not exceed a thickness of either the interference band or the clearance band. 
     
     
         3 . The cartridge of  claim 1 , wherein the continuous interior surface defines a change in inner diameter that is not mirrored by a corresponding change in outer diameter of the two-stage neck. 
     
     
         4 . The cartridge of  claim 1 , wherein the clearance diameter is consistent along the clearance band to the mouth of the two-stage neck, and the mouth has an inner diameter that is substantially equal to or greater than the clearance diameter. 
     
     
         5 . The cartridge of  claim 1 , wherein the projectile comprises an exterior surface that does not conform to the clearance band. 
     
     
         6 . The cartridge of  claim 1 , wherein at least a portion of the projectile is both coextensive with the clearance band and not in contact with the clearance band. 
     
     
         7 . The cartridge of  claim 1 , the clearance band comprising a cylindrical inner surface of substantially consistent diameter, the interference band comprising a cylindrical inner surface of substantially consistent diameter, and the exterior surface of the two-stage neck comprises a substantially cylindrical shape with a substantially consistent outer diameter along the neck length. 
     
     
         8 . The cartridge of  claim 1 , wherein the continuous interior surface of the transition portion is angled relative to a central axis of the case or curved between the interference band and the clearance band. 
     
     
         9 . The cartridge of  claim 1 , wherein the clearance diameter is greater than the interference diameter, and the transition portion comprises a gradual decrease in internal diameter from the clearance diameter to the interference diameter. 
     
     
         10 . The cartridge of  claim 1 , wherein the case further comprises a shoulder extending from the second end of the body to the two-stage neck, wherein the clearance band is configured to provide a clearance fit with the projectile, resulting in a radial gap between the clearance band and the projectile, and a majority of a length of the shoulder is not configured for contact with the projectile. 
     
     
         11 . The cartridge of  claim 1 , wherein an exterior of the two-stage neck comprises a reduced diameter relative to the body, the case further comprising a shoulder extending from the second end of the body to the two-stage neck, wherein the interference band extends from the shoulder to the clearance band, and the shoulder has a thickness that does not exceed a thickness of the interference band and the clearance band. 
     
     
         12 . The cartridge of  claim 1 , further comprising a sealant between at least a portion of the clearance band and at least a portion of the projectile. 
     
     
         13 . The cartridge of  claim 1 , wherein the interference band provides substantially an entire interference retention force of the projectile in the case. 
     
     
         14 . The cartridge of  claim 1 , wherein the case is configured for a cartridge of standardized cartridge dimensions comprising a predetermined projectile diameter, and wherein the neck length conforms to the standardized cartridge dimensions. 
     
     
         15 . The cartridge of  claim 1 , wherein the case is configured for a cartridge of standardized cartridge dimensions comprising a predetermined projectile diameter, and wherein the interference diameter is less than the predetermined projectile diameter and the clearance diameter is equal to or greater than the predetermined projectile diameter. 
     
     
         16 . The cartridge of  claim 1 , wherein the case comprises a material selected from steel and a steel alloy. 
     
     
         17 . A cartridge for a firearm, comprising:
 a projectile; and   a case, comprising:
 a base configured to hold a primer, 
 a body extending from a first end adjacent the base to a second end, and 
 a two-stage neck extending from the second end of the body to a forward mouth and configured to retain the projectile, the two-stage neck comprising:
 an interference band adjacent the second end of the body, the interference band having an interference diameter and configured to provide an interference fit with the projectile, 
 a clearance band forward of the interference band and having a clearance diameter greater than the interference diameter, the clearance band configured to provide one of a reduced interference fit with the projectile compared to the interference band, a line-to-line fit, or a clearance fit, and 
 a transition portion between the interference band and the clearance band, the transition portion comprising a continuous interior surface having a gradual decrease in inner diameter from the clearance diameter to the interference diameter, 
 wherein the interference band and the clearance band are at least partially coextensive with the projectile. 
 
   
     
     
         18 . The cartridge of  claim 17 , wherein the reduced interference fit is defined by the clearance diameter being less than a diameter of the projectile, wherein the line-to-line fit is defined by the clearance diameter being substantially equal to a projectile diameter, and wherein the clearance fit is defined by an interior surface at the clearance band being radially spaced from the projectile. 
     
     
         19 . A cartridge for a firearm, comprising:
 a projectile; and   a case, comprising:
 a base configured to hold a primer; 
 a body extending from a first end adjacent the base to a second end; and 
 a two-stage neck comprising an interior surface and an exterior surface, the two-stage neck extending from the second end of the body to a mouth, the mouth configured to receive therethrough the projectile, wherein the two-stage neck defines: 
 an interference band adjacent the second end of the body, the interference band having an interference diameter and extending an interference length along the two-stage neck, the interference diameter configured to provide an interference fit with the projectile resulting in an interference retention force, 
 a clearance band adjacent the mouth, the clearance band having a clearance diameter and extending a clearance length along the two-stage neck, the clearance diameter being greater than the interference diameter, 
 a transition portion located between and adjoining the interference band and the clearance band, and 
 a shoulder located between the body and the two-stage neck, wherein the shoulder has a radial wall thickness that is less than or equal to a radial wall thickness of either the interference band or the clearance band. 
   
     
     
         20 . The cartridge of  claim 19 , wherein the mouth is flared radially outwardly at both the interior surface and exterior surface.