Patent Publication Number: US-10782107-B1

Title: Lightweight cartridge case and weapon system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/587,727 filed on May 5, 2017 which is itself a continuation of U.S. patent application Ser. No. 15/587,660 filed on May 5, 2017, both of which claim the benefit under 35 USC § 119(e) of U.S. provisional patent application 62/334,620 filed on May 11, 2016. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The inventions described herein may be manufactured, used and licensed by or for the United States Government. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to small arms weapons and in particular to cartridge cases for small arms. 
     Centerfire ammunition cartridges have changed little since the 8 mm Lebel cartridge, developed in 1886, ushered in the modern era of high pressure centerfire cartridges. The evolution to the 8 mm Lebel ammunition cartridge began with the original design of a self-contained cartridge developed by Samuel Pauly and Francois Prelat in 1808 and includes the development of pin fired cartridges by Casmir Lefaucheux in 1836 and the breech loading Sharps rifle of the Civil War which initially fired paper cartridges but later adopted to fire self-contained metallic cartridges. Widespread adoption of self-contained metallic cartridge followed the development of the Smith &amp; Wesson Model 1 revolver in 1857. In 1867, the Eley-Boxer metallic centerfire cartridge case adopted by the British military. The 8 mm Lebel was the first cartridge using smokeless propellant to be made and adopted by any country. 
     Centerfire cartridges have changed little since these early developments. High power centerfire cartridges have used relatively thick, heavy cartridge case heads to support the firing loads. Most cartridge cases are made of heavy brass for this reason. Case head designs relying on mechanical extraction of the cartridge case require that the rearmost portion of the cartridge case extend beyond the rear of the chamber where they are largely unsupported. This, typically, limits peak chamber pressures to below 60,000 pounds per square inch (psi). High power centerfire cartridge cases constitute the majority of the weight of the complete cartridge. 
     Conventional ammunition includes a cartridge case  101 , a projectile  103 , a propellant  105  and a primer  107 . Prior art  FIG. 1  shows a conventional 5.56 NATO ammunition round known in the prior art. The 5.56 NATO ammunition round is the standard cartridge for NATO military forces as well other non-NATO military forces and is exemplary of the features and drawbacks of conventional ammunition. 
     The cartridge case  101  of the 5.56 NATO ammunition round is made of brass and the entire ammunition round weighs approximately 190 grains or 12.3 grams without any links for belt feeding. The cartridge case  101  accounts for a majority of this weight. The cartridge case  101  is a tapered bottleneck case type having a neck region  109 , a shoulder region  111 , a body region  113  and a head region  115 . The head region includes an extractor groove  117  and rim  119  for interfacing with a conventional extraction mechanism. 
     As illustrated by the 5.56 NATO ammunition round, the thickness of the head region  115  is substantially thicker than the thickness of the other regions of the cartridge case  101  due to both the need for the extraction features  117  in the case  101  and because the head region  115  of the case  101  is unsupported in the barrel. As the head  115  of the case  101  is unsupported, the material properties of the cartridge case  101  must be sufficient to withstand the firing load. The thicker head  115  adds additional size and weight to the cartridge case  101 . 
     The primer  107  is inserted into a cavity formed in the head  115  of the cartridge case  101 . The primer  107  also adds weight to the ammunition  10  and takes up volume within the cartridge case  101 . Additionally, the seam between the primer  107  and the cartridge case  101  may leak thereby causing performance issues with the ammunition round  2 . 
     A need exists for an improved ammunition cartridge which is lighter, less expensive, safer and can operate at higher chamber pressures than conventional ammunition. 
     SUMMARY OF INVENTION 
     One aspect of the invention is a rifle system. The rifle system comprises a rifle and an ammunition round for operation with the rifle. The high pressure ammunition round further comprises a cartridge case having an outer wall wherein prior to firing of the ammunition round, the outer wall geometry of the cartridge case is devoid of features configured for interfacing with a mechanical extractor. The rifle further comprising a barrel chamber which fully supports a chambered cartridge case and a rear extraction mechanism for extracting a spent cartridge case through the rear of the barrel chamber. 
     A second aspect of the invention is a rifle for firing high pressure ammunition. The rifle includes a barrel chamber which fully supports a chambered cartridge case and a rear extraction mechanism for extracting a spent cartridge case through the rear of the barrel chamber. 
     A third aspect of the invention is an ammunition round. The high pressure ammunition round further comprises a cartridge case having an outer wall wherein prior to firing of the ammunition round, the outer wall geometry of the cartridge case is devoid of features configured for interfacing with a mechanical extractor. 
     The invention will be better understood, and further objects, features and advantages of the invention will become more apparent from the following description, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
       Prior Art  FIG. 1  is a cross sectional view of a standard NATO 5.56 mm ammunition round, in accordance with one illustrative embodiment. 
         FIG. 2  is a sectional plan view of the rifle system in a chambered position, in accordance with one illustrative embodiment. 
         FIG. 3  is a sectional plan view of the rifle system in a firing position, in accordance with one illustrative embodiment. 
         FIG. 4  is a sectional plan view of the rifle system in an extraction position, in accordance with one illustrative embodiment. 
         FIG. 5  is a sectional plan view of a rifle comprising a gas extraction mechanism, in accordance with one illustrative embodiment. 
         FIG. 6  is a cutaway perspective view of the barrel chamber of the rifle comprising a recessed bolt extraction mechanism and a cartridge case in an uncaptured state, in accordance with one illustrative embodiment. 
         FIG. 7  is a cutaway perspective view of a barrel chamber of the rifle comprising a recessed bolt extraction mechanism and a cartridge case in a captured state, in accordance with one illustrative embodiment. 
         FIG. 8  is sectional plan view of a cartridge case with a consolidated propellant charge serving as the primer cup and anvil, in accordance with one illustrative embodiment. 
         FIG. 9  is a sectional plan view of a cartridge case with an integral primer cup, in accordance with one illustrative embodiment. 
         FIG. 10  is a sectional plan view of a percussion primed cartridge case with an integral primer cup, in accordance with one illustrative embodiment. 
         FIG. 11  is a sectional plan view of a cartridge case with a conventional primer cup, in accordance with one illustrative embodiment. 
         FIG. 12  includes  FIG. 12 a    which is a sectional plan view of a cartridge case with a conventional primer cup and non-tapered walls and  12   b  which is a sectional perspective view of a cartridge case with conventional primer cup and non-tapered walls, in accordance with one illustrative embodiment. 
         FIG. 13  includes  FIG. 13 a    which is a sectional plan view of a cartridge case with a hybrid cartridge case and a metal base and  FIG. 13 b    which is a sectional perspective view of a cartridge case with a hybrid cartridge case and a metal base, in accordance with one illustrative embodiment. 
         FIG. 14  is a plan view of a lightweight cartridge case with an annular groove, in accordance with one illustrative embodiment. 
         FIG. 15  is a sectional plan view of a lightweight cartridge case with an annular groove, in accordance with one illustrative embodiment. 
         FIG. 16  is a sectional plan view of a fired lightweight cartridge case with an annular groove where the annular groove has been fire formed to the chamber dimensions, in accordance with one illustrative embodiment. 
         FIG. 17  is a perspective view of a cartridge case with an integral linked belt, in accordance with one embodiment. 
         FIG. 18  is a perspective view of a cartridge case with an integral linked belt, in accordance with one embodiment. 
         FIG. 19  is a plan view of a cartridge case configured for linking with a string, in accordance with one embodiment. 
         FIG. 20  is a plan view of a cartridge case configured for linking with a string, in accordance with one embodiment. 
         FIG. 21  is a perspective view of multiple cartridge cases linked with a string, in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A rifle system having a rifle and accompanying ammunition allows for ammunition with a reduced weight cartridge case. The reduced weight of the cartridge case may lower the load on the soldier or may increase the performance of the rifle by allowing for more propellant to be included in an ammunition round. 
     Rifle, as used throughout this specification refers to a firearm which operates with peak chamber pressures in the range of approximately 40,000 to 190,000 pounds per square inch. The rifle may fire a single projectile or may fire projectiles in an automatic or semi-automatic firing mode. Additionally, the rifle may be either magazine fed or belt fed. As an example, conventional rifles which may be modified for use in the rifle system include the 5.7 mm P90, 5.56 mm M4, 5.56 mm M16/AR15, 7.62 mm M40 or M24 sniper rifles, .50 caliber M82A1/M107, 14.5 mm, 20 mm, 5.56 mm M249, 7.62 mm M240, .50 caliber M2, 20 mm M61, 25 mm M242, 30 mm GAU-8 and MK44, Bushmaster III 35/50 mm, 40 mm Bushmaster IV, 40 mm Bofors L/70, and Bofors 57 mm and other rifle calibers. However, the rifle isn&#39;t limited to modified versions of existing rifles. 
     The rifle includes a rear extraction mechanism which doesn&#39;t rely on an extractor groove as is typical of conventional centerfire cartridges. By eliminating the conventional extractor from the rifle, the barrel chamber may be modified to fully support the base of an ammunition round chambered in the rifle. 
     The ammunition round is suited for peak chamber pressures in the range of approximately 40,000 to 190,000 psi. More specifically, the ammunition round is particularly suited for peak chamber pressures in the range of approximately 50,000 to 150,000 psi. The lightweight ammunition round described herein may provide the equivalent functionality of conventional ammunition in a range of calibers. For example, the modified lightweight ammunition round may be a modified equivalent of the ammunition associated with the above listed firearms. 
     The ammunition round is devoid of the extractor groove found in traditional ammunition. Additionally, as the cartridge case is fully supported within the barrel, the cartridge case does not have to support the full firing load experienced during firing of the ammunition round. 
     Advantageously, the cartridge case is lighter than most conventional cartridge cases. The cartridge case requires less material to be used due to having thinner walls and the amount of head material being reduced. Additionally, alternative materials such as aluminum, steel or polymer materials may be used for the cartridge case as the full firing load is no longer supported by the cartridge case. 
     Weight reductions in the range of approximately 50% may be achieved over equivalent conventional ammunition. For example, as will be described in further detail below, in one embodiment in which a polymer case is employed, a belt fed modified lightweight 5.56 mm M855A1 ammunition round weighs approximately 96.3 grains whereas a belt fed conventional 5.56 mm M855A1 ammunition round weighs approximately 222 grains. 
     As the full support of the case addresses chamber pressure limitations associated with conventional ammunition, the lightweight cartridge case may be configured to operate at higher chamber pressures of the rifle to reduce the amount of propellant required to achieve a given muzzle velocity. Alternatively, the reduced weight and volume of the cartridge case may allow for the use of more propellant in the same weight and size profile of conventional ammunition thereby increasing performance. 
     In another embodiment, the lightweight ammunition rounds may include lightweight projectiles with high density penetrators to further reduce cartridge weight while providing increased lethality and armor penetration at short ranges due to the increased muzzle velocities associated with using lightweight projectiles. 
     A primer cup may be formed integrally to the cartridge case further reducing the volume and weight of the cartridge case. By having an integral primer cup and cartridge case, the ammunition round is more safe and robust as the seam between the primer cup and the cartridge case is eliminated. Additionally, eliminating this seam eliminates the “burn-through” failure mode associated with conventional high power cartridges with aluminum cases. 
     Additional safety features may be realized due to the case being fully supported. The risk of cook off is significantly reduced. During cook-off, the greatest hazard to the operator of the weapon is when the cartridge is partially chambered but the bolt is not locked. A conventional cartridge case ruptures at a high pressure due to the strength required by conventional cases. However, the relatively thin walls of the lightweight ammunition cartridge rupture at much lower and less hazardous pressure. Additionally, the hazard from fragments is lowered due to the lightweight, thin walled cartridge case failing at lower pressures and producing lower kinetic energy fragments compared to conventional brass cased cartridges. 
       FIG. 2  is a sectional plan view of the rifle system in a chambered configuration, in accordance with one illustrative embodiment. The rifle system includes a rifle  30  and an ammunition round  2 . As shown, the rifle system is in a chambered configuration with an ammunition round  2  chambered in the barrel  301  of the rifle  30 . The ammunition round  2  may be fed into the chamber  301  from a magazine using magazine feeding means known in the art. Alternatively, as will be described in further detail below, the ammunition round  2  may be belt-fed into the chamber. 
     The ammunition round  2  comprises a cartridge case  20 , a primer  26  and a propellant charge  24  housed within the cartridge case  20  and a projectile  22  secured to a forward end of the cartridge case  20 . As will be described in further detail below, in the embodiment shown, a primer composition  261  is secured inside the base  205  of the cartridge case  20  by the cartridge case  20  and the propellant charge  22  forming a primer cup  263 . The propellant charge  22  shown in  FIG. 2  is a consolidated propellant charge  22  which serves as an anvil  265  to ignite the primer composition  26 . Alternatively, an anvil  265  may be inserted between the propellant charge  22  and the primer composition  26 . 
     In a chambered configuration, the cartridge case  20  is seated in the chamber  301  of the barrel  301 . An inner surface of the barrel chamber  301  supports the entire length of the cartridge case  20  in the chamber, particularly including the region preceding the base of the cartridge case  20 . A bolt  303  of the rifle  30  is seated against an outer surface of the base  205  of the cartridge case  20 . A firing pin  305  of the rifle  30  is slidably disposed within the bolt  303 . 
       FIG. 3  is a sectional plan view of the rifle system in a firing configuration, in accordance with one illustrative embodiment. To fire the ammunition round  2 , the firing pin  305  strikes the base  205  of the cartridge case  20  thereby indenting the cartridge case  20 . The primer composition  261  is pinched between the indented cartridge case  20  and the anvil  265  of the propellant which initiates the primer composition  261 . Hot gases produced by the primer composition  261  reaction ignites the propellant charge  22 . Hot, high pressure gases pressure the chamber  301  and propel the projectile  22  thru a bore of the barrel  301 . 
       FIG. 4  is a sectional plan view of the rifle system in an extraction position, in accordance with one illustrative embodiment. Subsequent to firing the ammunition round  2 , the bolt  303  moves rearward. As the bolt  303  translates rearward, the fired cartridge case  20  is held against the bolt  303  by the residual pressure in the bore of the barrel  301 . As the cartridge case  20  travels rearward with the bolt  303 , an ejector engages the fired cartridge case  20  and redirects the cartridge case  20  out of an ejection port of the rifle  30 . Muzzle devices, such as conventional muzzle suppressors may be used to boost the duration and pressure of the residual bore pressure during case extraction. 
       FIG. 5  is a sectional plan view of a rifle comprising a gas extraction mechanism, in accordance with one illustrative embodiment. The duration and pressure of the residual bore pressure may be adjusted by trapping propellant gases during firing. Trapped propellant gases may then be reintroduced to the bore after firing to assist in extraction of the case. Alternatively, compressed gases from an external source may be introduced into the bore subsequent to firing to assist in ejection of the cartridge case  20 . The trapped gases may be stored in a gas housing  307  such as a cylinder or reservoir which is mounted to the barrel  301  and contains an inlet  309  to the bore of the barrel  301 . 
       FIG. 6  is a cutaway perspective view of the barrel chamber of the rifle comprising a recessed bolt extraction mechanism in an uncaptured position, in accordance with one illustrative embodiment. In an alternative embodiment, the rifle  30  comprises a dynamically formed extractor. In this embodiment, the bolt  303  comprises a recess  603  defined by the face  601  of the bolt  303 . The recess  603  is sized and dimensioned to receive a rear portion of the cartridge case  20  when pressed against the cartridge case  20 . The recess  603  further comprises an undercut  605 , such as a tapered undercut, defined by an inner circumferential surface of the recess  603 . 
       FIG. 7  is a cutaway perspective view of the barrel chamber of the rifle comprising a recessed bolt extraction mechanism and a cartridge case in a captured position, in accordance with one illustrative embodiment of the invention. In a chambered configuration of the rifle  30  system, the rear portion of the cartridge case  20  is received within the recess  603  with the recess  603  surrounding the rear portion. Upon firing of the ammunition round  2 , the thin walled cartridge case  20  expands into the undercut  605  thereby dynamically forming an extraction feature in the case. As the bolt  303  travels rearward, the cartridge case  20  is pulled along until interfacing with an ejector (not shown). The dynamically formed extractor may be employed in lieu of gas extraction of the cartridge case  20  or used in conjunction with gas extraction of the cartridge case  20 . 
     In an alternative embodiment, an interference extractor provides the extraction force on the cartridge case  20 . The interference extractor engages with the cartridge case  20  via an interference fit. The interference extractor pushes along the outer circumferential surface of the cartridge case  20  during feeding and chambering and provides adequate grip to extract the fired or unfired case. Advantageously, with such an interference extraction mechanism, both fired and unfired cartridge cases may be removed. An interference extractor is particularly suited for use with polymer cartridge cases. 
       FIG. 8  is sectional plan view of a cartridge case with a consolidated propellant charge serving as the primer cup and anvil  265 , in accordance with one illustrative embodiment. The exemplary ammunition round  2  shown in  FIG. 8  comprises a cartridge case  20 , primer composition  26 , propellant charge  22  and a projectile  22 . The cartridge case  20  shown in  FIG. 8  is a cylindrical straight-walled cartridge case  20 . The straight-walled cartridge case  20  is particularly suited for use with consolidated propellant charges as the straight walls do not impede the insertion of the propellant charge into the cartridge case  20 . However, in other embodiments, such as those embodiments which do not employ a consolidated primer charge, the walls are not straight and include a neck region and a shoulder region. 
     The cartridge case  20  shown in  FIG. 8  comprises a cylindrical body region  203  extending from the case mouth  201  to the base  205  of the cartridge case  20 . A base  205  of the cartridge case  20  is integral with the cylindrical body  203  of the cartridge case  20  and is of substantially the same thickness as the body  203  of the cartridge case  20 . The cartridge case  20  does not include a head region or rim and is devoid of any extractor features, such as the extractor groove, found on conventional ammunition. 
     The walls of the cartridge case  20  are of substantially the same thickness along the entire axial length of the body  203 . In comparison to conventional ammunition, the walls of the cartridge case  20  are relatively thin. In particular, the absence of the thicker head region and base  205  reduces the volume of case material required for the cartridge case  20 . 
     Accordingly, as the head region and extraction features are eliminated and the cartridge case  20  walls are thinner, the cartridge case  20  is lighter. Additionally, the reduction in material allows for the lightweight ammunition round  2  to achieve the same performance as an equivalent conventional ammunition in a smaller profile round. Alternatively, the lightweight ammunition round  2  may have the same outer profile as an equivalent conventional ammunition with more volume available in the interior cavity. This additional volume may be utilized to increase performance by including more propellant in the round. 
     To further reduce cartridge weight, the ammunition round  2  may be made of lighter and cheaper materials than conventional ammunition. As the ammunition round  2  is fully supported within the chamber, materials with the strength of brass are not required. For example, the ammunition cartridge may be made of steel, aluminum or a polymer material. The polymer material may be a sulfone polymer material such as Radel® polyphenylsulfone (PPSU) material available from Sulvay S.A. located in Neder-Over-Heembeek, Brussels, Belgium. However, the ammunition cartridge is not limited to being made of steel, aluminum or polymer. The cartridge case  20  may be made of any material suitable to withstand chamber pressures in the ranges specified above. 
     The body  203  and base  205  together define an interior cavity of the cartridge case  20  with an opening at the mouth  201  of the cartridge case  20 . A projectile  22  is inserted into the interior cavity of the cartridge case  20 . Primer composition  261  and a propellant charge  22  fill the remaining volume of the cavity. 
     In the embodiment shown, the propellant charge  22  is a consolidated propellant charge  22  which serves to secure the primer composition  261  within the interior cavity as well as to serve as the anvil  265  for initiating the primer composition  26 . The consolidated propellant charge  22  comprises a cavity for receiving the primer composition  261  formed in a bottom surface of the charge. The bottom surface of the consolidated propellant charge  22  is in communication with the primer composition  261  and is of sufficient strength to serve as the anvil  265 . In alternative embodiments of the invention, an external anvil  265  may be inserted into the inner cavity and between the propellant charge  22  and the primer composition  261 . Additionally, the propellant is not limited to consolidated propellants. The propellant may be compacted in the cartridge case  20 , as well. 
     In addition to the weight reductions and performance enhancements achieved through the cartridge case  20  dimensions and material properties, as the cartridge case  20  is fully supported within the chamber, the rifle  30  and ammunition round  2  may be configured to operate at higher chamber pressures. Accordingly, less propellant may be required in the lightweight ammunition round  2  to achieve the same results as conventional ammunition. This serves to further reduce the volume and weight of the ammunition round  2 . 
     In operation, the firing pin  305  strikes the base  205  of the cartridge case  20  which pinches the primer composition  261  between the cartridge case  20  and the propellant charge  22  or anvil  265 . Advantageously, as the primer composition  261  is secured by the propellant charge  22 , a peripheral primer cup and the associated added weight, cost and complexity are eliminated. 
     The weight of the lightweight ammunition round  2  is approximately 50% lighter than an equivalent conventional ammunition round. For example, the M855A1 ammunition round with an M27 metallic belt has a total weight of approximately 222 grains. The conventional brass case comprises 105 grains. The conventional propellant weighs approximately 22 grains. The projectile weighs approximately 62 grains. The conventional primer weighs approximately 3.2 grains with the primer cup and anvil accounting for approximately 3 grains. The link weighs 30 grains. 
     In comparison, an equivalent lightweight ammunition round  2  having a polymer cartridge case  20  and operating at a peak chamber pressure of 100,000 pounds per square inch and having a muzzle velocity equivalent to a convention M855A1 weighs approximately 97 grains. The polymer cartridge case  20  of the ammunition round  2  weighs approximately 15 grains. This is 90 grains, or approximately 86%, lighter than a conventional cartridge case. The propellant charge weighs approximately 18 grains. Note that due to the higher chamber pressures enabled by fully supporting the cartridge case  20 , less propellant is required to achieve the same muzzle velocity as the conventional M855A1. The projectile weighs approximately 62 grains. The primer weighs approximately 1 grains. The polymer link weighs approximately 1 grain. 
     The ammunition round  2  described above is one embodiment of the invention. Individual components may be modified according to application to increase or decrease the performance. For example, the above weights are for a percussion primed cartridge case  20 . Alternatively, laser ignition may be utilized to ignite the primer composition thereby negating the need for an anvil and further reducing the weight by at least 1 grain. 
       FIG. 9  is a sectional plan view of a cartridge case with an integral primer cup, in accordance with one illustrative embodiment. The cartridge case  20  shown in  FIG. 9  is a bottleneck cartridge having a neck region  207  and a shoulder region  209 . The lightweight cartridge case  20  is devoid of a head region, rim and extraction features of conventional ammunition. 
     The cartridge case  20  further comprises a primer cup  263  integral to the cartridge case  20 . The primer cup  263  is formed in the interior surface of the base  205  of the cartridge case  20  and holds the primer composition  26 . An anvil  265  sits above the primer composition  261  and between the primer composition  261  and the propellant charge  22  and further secures the primer composition  261  in the primer cup  263 . The anvil  265  is attached to the cartridge case  20  by a thread, crimp, weld, adhesive, or other means and may be made of brass, steel, aluminum, polymer or a combustible material. The anvil  265  further comprises one or more flash tubes  267  for directing the hot gases of the primer composition  261  to the propellant charge  22 . 
     In operation, the base  205  of the cartridge case  20  is indented by the firing pin  305 . The primer composition  261  is pinched between the base  205  of the cartridge case  20  and the anvil  265 . Hot gases are produced by the primer composition  261  and directed to the propellant charge  22  by the flash tubes  267 . As the propellant does not secure the primer composition  261  or serve as the anvil  265 , the propellant may be a non-consolidated propellant. 
     Advantageously, the joint between the primer cup and the cartridge that exists in conventional ammunition is eliminated. This also reduces the weight associated with the conventional metallic separately loaded primer. For aluminum cartridge cases, the integral primer cup  263  eliminates the potential for “burn through” by eliminating the potential leak path at the joint between the case and the primer cup. For polymer cartridge cases, the integral primer cup eliminates the need for a primer support typically used in polymer cartridge cases, including conventional polymer cartridge cases and polymer cased telescoped cartridge cases. 
       FIG. 10  is a sectional plan view of a percussion primed cartridge case  20  with an integral primer cup, in accordance with one illustrative embodiment. The cartridge case  20  shown in  FIG. 10  is a polymer cartridge case  20  having an integral primer cup  263 . The cartridge case  20  is a bottleneck cartridge having a neck region  207  and a shoulder region  209 . While the lightweight cartridge case  20  is devoid of a rim and extraction features of conventional ammunition, the cartridge case  20  comprises a head region  211  surrounding the integral primer cup  263  and anvil  265 . A recess is formed in the base  205  of the cartridge case  20  for serving as the primer cup  263  and receiving the anvil  265 . 
       FIG. 11  is a sectional plan view of a lightweight cartridge case with a conventional primer cup, in accordance with one illustrative embodiment. The cartridge case  20  is not limited to having an integral primer cup  263 . The embodiment shown in  FIG. 11  is configured for receiving a peripheral primer  26  such as a Berdan primer  26 . 
     The cartridge case  20  is a bottleneck cartridge case  20  having uniformly thin walls for the base  205  and body  203  of the cartridge case  20 . The cartridge case  20  further comprises a neck region  207  and shoulder region  209  and is devoid of a head region and extraction features. A recess for receiving the primer cup  263  is defined by the outer surface of the base  205  and extends into the interior cavity of the cartridge case  20 . Unlike conventional cartridge cases, the primer cup recess  213  is not surrounded by a head region of the cartridge case  20 . An opening is formed in the base  205  of the primer cup recess  213  thereby allowing the gases of the primer to interact with the propellant charge  24  of the interior cavity. 
       FIG. 12  includes  FIG. 12 a    which is a sectional plan view of a cartridge case  20  with a conventional primer and non-tapered walls and  12   b  which is a sectional perspective view of a cartridge case  20  with conventional primer and non-tapered walls, in accordance with one illustrative embodiment. The cartridge case  20  shown in  FIG. 12 a    and  FIG. 12 b    is a straight wall cartridge case  20  having a base  205  configured for receiving a peripheral primer  26 . 
     The cartridge case  20  comprises a body region  203  having thin walls, a head region  211  and a base  205 . There is an opening in the head for receiving a base  205  and the interior surface of the head region  211  has mating features for interfacing with and connecting to a peripheral base  205  of the cartridge case  20 . The base  205  and head region  211  may be of the same material or may be different materials. 
     The base  205  comprises reciprocal mating features for interfacing and connecting to the head region  211  and is further configured for receiving a peripheral primer  26 , such as a Berdan primer. The base  205  comprises a recess defined by the outer facing surface of the base  205  for receiving the primer  26 . An opening is formed in the base of the primer cup recess  213  thereby allowing the gases of the primer composition to interact with the propellant charge  24  of the interior cavity. 
       FIG. 13  is a sectional plan view of a cartridge case with a hybrid cartridge case and a metal base, in accordance with one illustrative embodiment. In the embodiment shown in  FIG. 13 , the cartridge case  20  is a straight-walled case having a polymer body region  203  and head region  211  and a metal base  205 . The body region  203  comprises thin walls and defines the inner cavity of the cartridge case  20 . 
     The head region  211  extends from the cartridge case  20  forming the base of the interior cavity further defines the primer cup  263 . A primer cup recess  213  is formed in the head region  211  defined by the bottom surface of the head  211  and extended axially into the head region  211 . The head region  211  further comprises integrally formed primer features including an anvil  265  and one or more flash tubes  267 . The head  211  is dimensioned for being partially inserted into the metal base  205 . The base  205  of the cartridge case  20  is a hollow metal cylinder with an opening formed in the proximate end of the cylinder. 
       FIG. 14  is a plan view of a lightweight cartridge case with an annular groove, in accordance with one illustrative embodiment.  FIG. 15  is a sectional plan view of a lightweight cartridge case with an annular groove, in accordance with one illustrative embodiment. The ammunition round  2  may be magazine fed or belt fed into the chamber  301  of the rifle  30 . For the ammunition round  2  to be belt fed by a conventional push through belt, such as an M27 ammunition belt, M13 ammunition belt or the M15 ammunition belt, an annular groove  221  is formed in the outer circumferential surface of the cartridge case  20 . The annular groove  221  interfaces with a rear tab of a push through belt. 
     The lightweight cartridge case  20  is a bottleneck cartridge comprising a neck region  207 , shoulder region  209 , body region  203  and base  205 . The cartridge case  20  has thin walls in each region. A recess is formed in the base  205  to receive a peripheral primer. However, in other embodiments, the primer may be integral to the cartridge case  20 . 
     The annular groove  221  is located near the base  205  of the cartridge case  20  in place of the extractor groove found on a conventional cartridge case. The annular groove  221  may be machined into the cartridge case  20 . Alternatively, the annular groove  221  may be grove rolled into the cartridge case  20 . In the embodiment shown in  FIG. 15 , the annular groove  221  does not increase the wall thickness at the annular groove  221  thereby maintaining the weight, volume and material savings achieved by the lightweight ammunition round  2 . 
       FIG. 16  is a sectional plan view of a fired lightweight cartridge case with an annular groove where the annular groove has been fire formed to the chamber  301  dimensions, in accordance with one illustrative embodiment. In operation, a straight wall body  203  may be fire formed. Subsequent to the firing of the cartridge case  20 , the hot gases within the cartridge case  20   20  may provide a force against the interior cavity of the cartridge case  20  such that the annular groove  221  is deformed and the cartridge case  20  conforms to the interior geometry of the barrel chamber  301 . 
       FIG. 17  is a perspective view of a cartridge case with an integral linked belt, in accordance with one embodiment. In an embodiment of the invention, the cartridge case  20  is a polymer case with an integral linked belt  291  for linking multiple cartridge cases  20   a . . . n . The integral linked belt  291  comprises one or more protrusions  293  integral to the cartridge case  20  and extending radially out from the outer circumferential surface of the cartridge case  20 . Each protrusion  293  links the cartridge case  20  to another cartridge case  20 . By linking a plurality of ammunition rounds  2  sequentially, an integral linked belt  291  for feeding the ammunition into the chamber  301  of the rifle  30  is formed. 
     In the embodiment shown in  FIG. 17 , each cartridge case  20  comprises four integral links  293  (i.e. protrusions  293 ). However, the cartridge case  20  is not limited to four integral links  293 . There may be more than four links  293  or less than four links  293  dependent on the application. Two integral links  293  extend radially out from a right side of the cartridge case  20  to link the cartridge to a preceding cartridge case  20 . Two integral links  293  extend radially out from the left side of the cartridge case  20  to link the cartridge case  20  to a subsequent cartridge case  20 . Advantageously, the integral link belt  291  may be fed from a forward end or a back end as it is reversible. 
     Each protrusion  293  extends from a recessed portion  295  of the cartridge case  20  extending around the circumference of the cartridge case  20  and having a width along the axial direction of the cartridge case  20 . The recessed portion  295  of the cartridge case  20  has an outer diameter that is smaller than the outer diameter of the non-recessed portions of the body  203  of the cartridge case  20 . The recessed portion  295  is located at a mid-section of the body  203  of the cartridge where the cartridge case  20  is well-supported by the chamber  301  during firing. By locating it away from the base  205  or shoulder of the cartridge case  20 , case failure during firing may be avoided. Additionally, the non-recessed portions of the cartridge case  20  in the axial and distal ends of the cartridge case  20  seal the chamber  301  and experience the most demanding conditions during firing. 
     The rifle  30  further comprises a detachment mechanism, such as a blade. During the process of feeding the ammunition round  2  into the chamber  301  of the barrel  301 , the detachment mechanism cuts the relatively thin polymer protrusion  293  to separate the round about to be chambered. While the round is being chambered, the cut protrusion  293  is forced to wrap into the recessed portion of the cartridge case  20 . 
     The protrusion  293  may be molded or co-molded to the cartridge cases  20 . One preferred material for the cartridge case  20  and integral link is Radel® polyphenylsulfone (PPSU) material available from Sulvay S.A. located in Neder-Over-Heembeek, Brussels, Belgium. Radel® PPSU provides the necessary strength, flexibility and impact resistance while still being easily cut. 
       FIG. 18  is a perspective view of a cartridge case  20  with an integral linked belt, in accordance with one embodiment. In an alternative embodiment of the case, the integral links  293  may extend out from the outer surface at an angle as opposed to radially. In the embodiment shown in  FIG. 18 , two integral links  293  extend from the right outer surface of the cartridge case  20  at an angle of 45 degrees with respect to a central axis of the cartridge case  20 . Each of the two links is connected to an integral link  293  from a preceding cartridge case  20  thereby forming a “v” shape. 
       FIG. 19  is a plan view of a cartridge case  20  configured for linking with a string, in accordance with one embodiment. In an embodiment of the invention, the cartridge cases  20  are linked via a string link  297 . The string  297  can be attached either during case molding or subsequent to case molding. The cartridge case  20  comprises one or more string link grooves  299  extending annularly along the outer circumferential surface of the cartridge case  20 . The one or more grooves  299  are employed to secure the string link  297  in the proper location for the link configuration that is attached after the case is molded. 
     A weak point can be engineered at the midpoint in the string link  297  between cartridges. The weak point may be a knot in the string or may be a laser cut. 
     Advantageously, the string link  297  is more flexible, stronger and lighter than a link made from the cartridge case  20  material. Additionally, the string  297  is received into the annular grooves  299  thereby providing a smoother outer profile to aid chambering of the ammunition round  2 . 
     In the embodiment shown in  FIG. 19 , the cartridge case  20  comprises two annular string link grooves  299 . The outer diameter of the body  203  of the cartridge case  20  is uniform except for the two annular grooves  299 . 
       FIG. 20  is a plan view of a cartridge case  20  configured for linking with a string, in accordance with one embodiment. In the embodiment shown in  FIG. 20 , the cartridge case  20   a . . . n  comprises two annular string link grooves  299 . The string link grooves  299  are disposed in a recessed portion  295  of the body  203  having an outer diameter smaller than the outer diameter at the front end and back end of the cartridge case  20 . The recessed portion  295  may aid chambering of the round as the broken string link sits in the recess  295  and not between the chamber  301  and the cartridge case  20 . 
       FIG. 21  is a perspective view of multiple cartridge cases linked with a string, in accordance with one embodiment. The string links  297  connect the cartridge case  20  to a preceding and a subsequent cartridge case  20  thereby forming a belt of ammunition. Advantageously the belt may be fed from either end. 
     While the invention has been described with reference to certain embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.