Hybrid cartridge with improved primer insert

Abstract

A hybrid ammunition cartridge includes a metal disc having a primer pocket formed in one side in fluid communication with a flash hole defined through an opposite side. A polymer cartridge body is molded over the metal disc from the first side to the second side. The polymer body encloses a propellant chamber, forms an extraction flange around the perimeter of the metal disc, and also forms the base end of the cartridge. A perforated flash hole extension may extend into the propellant chamber to ensure uniformity of internal pressure during ignition thereby improving accuracy of a projectile discharged from the cartridge.

Description

BACKGROUND OF THE INVENTIONField of the Invention

[0001] The present invention relates generally to ammunition cartridges for firearms, and more specifically, to hybrid polymer-metal ammunition cartridges and methods of making the same.Description of Related Art

[0002] Conventional ammunition cartridges have long been made from brass, which is expensive, heavy, and potentially hazardous. In terms of military use, the weight of brass cartridges en masse adds significantly to the overall weight a soldier or vehicle must carry. This limits the amount of brass cartridges that the individual soldier can carry on their person and presents further logistical issues for transportation and use by military vehicles. For instance, a box of .050 caliber brass ammunition cartridges (approximately 100 cartridges) plus links can weigh about 35 pounds.

[0003] Thus, there has long been a need for a lighter weight alternative to the conventional brass ammunition cartridge. Polymer cartridges have been considered a desirable alternative to brass cartridges for decades but prior polymer cartridges have not yet met industry and military performance standards.

[0004] Prior attempts to manufacture polymer cartridges have resulted in the random occurrence of structural failures at discrete points of the cartridge body upon firing. Among these failures, there were typically no obvious external deformations that could provide the shooter with notice that the cartridge may be defective. Rather, due to inherent variations in the manufacturing process, in each case a discrete portion of a cartridge was out of tolerance from the required specification, thereby weakening that portion of the cartridge. For example, the weakened or defective potion of the cartridge may have resulted from an undesirable thinning of the cartridge wall during molding. The reduction to wall thickness is typically not visible externally, which allows the defective cartridge to pass into circulation and eventually be fired in a firearm.

[0005] Firing a structurally compromised polymer cartridge poses significant safety risks to the operator. For instance, the explosion of the primer and subsequent ignition of the propellant powder can cause the base end of the cartridge to be blown away from the cartridge body. This may cause the firearm to jam, which can be very dangerous in military or law enforcement scenarios where a sustained rate of fire might be necessary. Further, depending on the timing of the blowout, the cartridge may not build up enough pressure to propel the bullet out of the firearm.

[0006] The prior solution to addressing base end blowouts in polymer cartridges has been to utilize a machined metal piece to form the base. The metal piece is typically partially overmolded to connect it with the remainder of the cartridge body. However, the machined metal base end piece is expensive and time consuming to manufacture, thus increasing the manufacturing costs. Further, base end blowouts may still be present, albeit at a reduced occurrence, in these prior art polymer cartridges, despite the use of the expensive machined base piece.

[0007] Thus, what is needed is a more reliable polymer-based cartridge that is structurally sound and can resist blowouts.SUMMARY OF THE INVENTION

[0008] The above problems are overcome with a hybrid cartridge according to the present invention. The disclosed hybrid cartridge has an overall weight that is less than the conventional metal cartridge of equivalent caliber while maintaining a high degree of structural integrity. The hybrid cartridge disclosed herein can be manufactured in virtually any caliber of pistol or rifle cartridge for civilian, military and law enforcement uses.

[0009] In one embodiment, the hybrid cartridge includes a metal disc having a primer pocket formed in a first side and a flash hole defined through an opposite second side. The flash hole fluidically connects the primer pocket to the second side of the metal disc. A polymer body is molded over the metal disc from the first side to the second side. The polymer body forms an extraction flange around the perimeter of the metal disc and further forms the base end of the cartridge. A projectile opening is defined at the forward end of the polymer body and opens into an internal propellant chamber. In preferred embodiments, the internal surface of the primer pocket and internal surface of the flash hole are metal and remain free from polymer material. The polymer body preferably completely encloses the metal disc while leaving the primer pocket and flash hole free of polymer material.

[0010] In some embodiments, the outer diameter of the metal disc may be less than a maximum outer base diameter required for a standard cartridge of equivalent caliber. The extraction flange thereafter forms a second outer diameter that is substantially equal to the maximum outer base diameter for the standard cartridge.

[0011] In preferred embodiments, the primer pocket is configured to receive a small rifle primer. The depth of the primer pocket formed in the metal disc in combination with the thickness of polymer forming the base end is substantially equal to the height of an industry standard small rifle primer. In some embodiments, the polymer body may also include an annular shoulder formed around the projectile opening. In further embodiments, the annular shoulder may transition into a neck to form a bottleneck cartridge.

[0012] In some embodiments, the metal disc may include texturing configured to increase the surface adhesion with the polymer material from the polymer body. The first side of the metal disc may be textured or the second side may be textured or both sides of the metal disc may be textured.

[0013] In further embodiments, the hybrid cartridge may include a metal disc having a primer pocket formed in a first side and an extended flash hole extending from the opposite second side. A polymer body is molded over the metal disc from the first side to the second side. The polymer body forms an extraction flange around the perimeter of the metal disc. A projectile opening is defined at the distal end of the polymer body. An internal propellant chamber is formed between the metal disc and the projectile opening. In preferred embodiments, the extended flash hole extends into the propellant chamber, preferably at least 10% of the overall length of the cartridge. In some embodiments, the polymer body may include an annular shoulder formed around the projectile opening. The shoulder may further transition into a neck that terminates in the projectile opening to form a bottleneck cartridge.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. Component parts shown in the drawings are not necessarily to scale, and may be exaggerated to better illustrate the important features of the invention. Dimensions shown are exemplary only. In the drawings, like reference numerals may designate like parts throughout the different views, wherein:

[0015] FIG. 1 is a side view of an embodiment of a hybrid cartridge according to the present invention.

[0016] FIG. 2 is a cross-sectional view, taken along line A-A marked in FIG. 1, of an embodiment of a hybrid cartridge according to the present invention.

[0017] FIG. 3 is a top view of an embodiment of a primer disc according to the present invention.

[0018] FIG. 4 is a cross-sectional view, taken along line B-B marked in FIG. 3, of an embodiment of the primer disc.

[0019] FIG. 5 is a cross-sectional view of an alternative embodiment of a hybrid cartridge according to the present invention, with the section view similarly taken along line A-A marked in FIG. 1.

[0020] FIG. 6 is a flow chart diagramming the salient steps for a first embodiment of a method for manufacturing a hybrid cartridge according to the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0021] The following disclosure presents exemplary embodiments of a hybrid polymer ammunition cartridge that has an improved internal structure to resist blowouts at the base end. The inventive cartridge may be referred to as a hybrid cartridge throughout the following disclosure. The cartridge is a “hybrid” because it includes both metal and polymer to form the structure of the cartridge. The hybrid cartridge disclosed herein weighs less than a conventional metal cartridge of the same caliber but meets the same levels of consistency in terms of firing and structural reliability.

[0022] Use of the term “polymer” throughout this disclosure shall be interpreted in a non-limiting fashion and given broad interpretation according to its plain and ordinary meaning. “Polymer” can mean a natural polymer or a synthetic polymer. Examples of polymers as used herein include but are not limited to acrylic, polyethylene, polyolefin, polypropylene, polystyrene, polyvinylchloride, synthetic rubber, phenol formaldehyde, neoprene, nylon, polyacrylonitrile, PVB, silicone, and any of the foregoing in powdered, micronized powdered, or resin form. The polymer can further be homogenously mixed with one or more conventional filler materials, such as glass fibers, ceramics, carbon fibers and other types of metallic fillers (e.g., copper, aluminum, nickel, iron, etc. in powdered or flake form).

[0023] To ensure safety and compatibility across different manufacturers and producers of ammunition cartridges and firearms, many industry participants opt to voluntarily follow the conventional “industry standard” when manufacturing a particular caliber of ammunition cartridge or firearm. In the firearms and ammunition industry, there are several entities that periodically publish “industry standard” drawings that establish maximum cartridge dimensions for a specific caliber and the corresponding minimum firearm chamber dimensions for the same caliber. Inclusive to these industry standard dimensions, and particularly relevant to the claimed invention, is the industry standard primer sizes and the corresponding primer pocket dimensions formed in the cartridge. Industry participants whose products conform to these dimensional standards can ensure that their cartridges will be compatible with corresponding firearms, or vice versa, regardless of the manufacturing source for each component. The entities responsible for setting the industry standards include the Sporting Arms and Ammunition Manufacturers'Institute, Inc. (“SAAMI”), the Permanent International Commission for the Proof of Small Arms (“CIP”), and the North Atlantic Treaty Organization (“NATO”).

[0024] Thus, the phrase “industry standard” as used throughout this disclosure refers to those standards for the maximum cartridge and minimum chamber dimensions set by entities such as SAAMI, CIP and NATO. These industry standards are well known to the artisan skilled in the ammunition and firearms industry and the scope of such phrase is readily appreciated by such artisans.

[0025] FIG. 1 is a side view of an embodiment of a hybrid cartridge according to the present invention. The hybrid cartridge 10 includes a polymer body 12 extending from the base end 14 to the projectile opening 16. The polymer materials from the polymer body 12 form the base end 14. The polymer body 12 forms an extraction flange 18 around the diameter of the base end 14. The polymer body 12 may extend into an annular shoulder 20 that transitions into a cartridge neck 22. The projectile opening 16 is defined at the end of the cartridge neck 22. It should be understood that while FIG. 1 illustrates the hybrid cartridge as a bottleneck cartridge, the invention can be implemented in conventional straight-walled cartridges as well as in nonconventional neckless ammunition cartridges.

[0026] FIG. 2 is a cross-sectional view, taken along lines A-A marked in FIG. 1, of an embodiment of a hybrid cartridge according to the present invention. The polymer body 12 forms an internal propellant chamber 24. The polymer body 12 also encloses a metallic primer disc 26 at the base end 14 of the hybrid cartridge 10. The primer disc 26 includes a primer pocket 28 formed therein and in fluid communication with the propellant chamber 24 through a flash hole 30. The polymer body 12 is molded completely over the primer disc 26 while leaving bare the primer pocket 28 and flash hole 30. The bottom surface 25 of the propellant chamber 24 is formed from the polymer material of the polymer body 12. Similarly, the base end 14 is formed from the polymer material of the polymer body 12. The primer pocket 28 and the flash hole 30 are metal, formed during a stamping process for the primer disc 26, as detailed further below. The primer pocket 28 and the flash hole 30 remain free of polymer material. A primer that is loaded into the hybrid cartridge 10 is therefore limited to an internal metallic structure so that the initial primer explosion is sufficiently contained and does not structurally weaken the polymer body 12. The extraction flange 18 is fully formed from the polymer material of the polymer body 12. In preferred embodiments, the polymer body 12 is molded to included a thickness 19 of polymer between the outer diameter of the primer disc 26 and the outer diameter of the extraction flange 18. The thickness 19 may be altered by changing the size of the primer disc 26, e.g., increasing or decreasing the outer diameter of the primer disc 26. Further, the thickness 19 may increase as the caliber of the hybrid cartridge 10 is increased, e.g., larger caliber hybrid cartridges may require an increase to the thickness 19 to ensure the structural integrity is maintained.

[0027] FIG. 3 is a top view of an embodiment of the primer disc 26 according to the present invention. In preferred embodiments, the primer disc 26 is substantially circular. The flash hole 30 is defined through the center point of the primer disc 26 and the primer pocket 28 is concentrically aligned with the flash hole 30.

[0028] The outer diameter OD of the primer disc 26 is less than the standard outer base diameter for a conventional industry standard cartridge in a given caliber. The thickness 19 of polymer material forming the extraction flange 18 builds up the outer diameter at the base end 14 off the primer disc 26 until it is substantially equal to the base diameter required by industry standards for that caliber. In preferred embodiments, the outer diameter OD of the primer disc 26 is between about 10% to about 25% less than the standard outer diameter of the base end 14. In most preferred embodiments, the outer diameter OD of the primer disc 26 is about 15% less than the standard outer diameter of the base end 14. In one example, the hybrid cartridge 10 may be a 308 Winchester cartridge according to industry standards. The standard 308 Winchester cartridge requires an outer diameter at the base end 14 substantially equal to 0.473 inches. In this example, the outer diameter OD of the primer disc 26 may therefore be between about 0.355 inches to about 0.428 inches, and most preferably about 0.402 inches. In this most preferred embodiment, the extraction flange 18 has a radial thickness 19 substantially equal to 0.0355 inches so that the final outer base diameter for this hybrid cartridge 10 is substantially equal to the required 0.473 inches.

[0029] The structural integrity of the hybrid cartridge 10 is achieved and maintained throughout the firing and subsequent extraction processes due to the sandwiching or pinching arrangement of the primer disc 26 with the polymer body 12. When the hybrid cartridge 10 is loaded in a firearm, the base end 14 will be supported against the bolt face and the polymer body 12 is supported by the firearm chamber. Upon initial firing, the explosion from the primer will ignite the powder charge in the propellant chamber 24. The primer explosion and powder ignition will produce a pinching effect on the primer disc 26 where the bolt face will exert a force in a first direction against the base end 14 and the powder ignition exerts a second force in the opposite direction against the bottom surface 25 of the propellant chamber 24. These opposing forces pinch the primer disc 26 between the polymer material forming the base end 14 and the bottom surface 25 of the propellant chamber 24 thereby increasing the structural integrity of the hybrid cartridge 10.

[0030] FIG. 4 is a cross-sectional view taken along line B-B in FIG. 3 of an embodiment of a primer disc according to the present invention. In preferred embodiments, the primer pocket 28 is sized to fit an industry standard “small rifle” primer, which has a diameter of about 0.1745 inches and a height of about 0.115 inches. In preferred embodiments, the depth of the primer pocket 28 is less than the depth required by industry standards for a small rifle primer. This is to allow polymer material to flow over the primer disc 26 to form the base end 14. The depth of the primer pocket 28 inclusive of the thickness 15 of polymer material forming the base end 14 is therefore substantially equal to the depth required for an industry standard small rifle primer pocket, e.g., depth of substantially 0.117 inches. The primer pocket 28 is stamped in the first side 32 of the primer disc 26 and the flash hole 30 is defined through the second side 34. In some embodiments, the first side 32 and the second side 34 may be textured to increase surface adhesion of the polymer material thereto during the manufacturing process.

[0031] FIG. 5 is a cross-sectional view of an alternative embodiment of a hybrid cartridge according to the present invention. The cross-section is similarly taken along line A-A marked in FIG. 1. The hybrid cartridge 40 is substantially similar to the hybrid cartridge 10 described above. The primary difference between hybrid cartridge 10 and hybrid cartridge 40 is found in the structure of the primer disc. The hybrid cartridge 40 includes an extended primer disc 42 that has a flash hole extension 44 formed to extend from an upper side 46 of the primer disc 42. A primer pocket 48 is formed in the lower side 50 and is concentrically aligned with the flash hole extension 44. The flash hole extension 44 extends a defined length into the propellant chamber 24. In preferred embodiments, the flash hole extension 44 has a length that is between about 5% to 50% the overall axial length of the hybrid cartridge 10 as determined by industry standards.

[0032] Continuing with the above 308 Winchester example, industry standards require the overall axial cartridge length L to be substantially equal to 2.015 inches. The length of the flash hole extension 44 may therefore be between about 0.1007 inches to about 1.0075 inches so that the flash hole extension 44 extends a defined distance into the propellant chamber 24. The flash hole extension 44 connects the primer pocket 48 to a more central portion of the propellant chamber 24. The flash introduced to the central portion of the propellant chamber 24 by the flash hole extension 44 generates a more uniform internal pressure column thereby improving accuracy of the hybrid cartridge 10 by decreasing turbulence in the ignition of the internal powder charge.

[0033] In more elaborate embodiments of the hybrid cartridge 40, the flash hole extension 44 may include a plurality of perforations defined through the wall of the flash hole extension. The perforations fluidically connect the primer pocket 48 to the propellant chamber 24 at varying depths to provide a more uniform powder ignition upon firing of the hybrid cartridge 40. The perforations may be vertically stacked at regular intervals and radially separated by a defined angle. In some preferred embodiments, the perforations may be vertically stacked every 0.100 inches and offset by a 120-degree angle so that there are three columns of perforations symmetrically formed in the flash hole extension 44. In alternative embodiments, each vertical stack of perforations may be radially offset by a substantially 90-degree angle. The perforated flash hole extension reduces the velocity of the initial primer explosion to more uniformly ignite the internal powder charge. The result of increasing the uniformity of the propellant ignition is an increase to the accuracy of the projectile discharged from that cartridge. The release of the projectile from the cartridge is effectuated more smoothly to provide a more stable flight down the barrel and out of the firearm muzzle which translates to a more stable flight to target.

[0034] FIG. 6 is a flow chart diagramming the salient steps for a method of manufacturing a hybrid cartridge according to one embodiment of the present invention. The method 100 can be used to manufacture the hybrid cartridge 10 and the hybrid cartridge 40 described above. With regard to the following discussion, the method 100 will be discussed generally with respect to hybrid cartridge 10. The method 100 begins with stamping 102 the primer disc 26. Preferably, the primer disc 26 is stamped from a metal sheet, such as a copper or steel sheet. The outer diameter OD of the primer disc 26 is set during the stamping step 102. As discussed above, the dimension of the outer diameter OD is caliber dependent to allow for control of the thickness 19 of polymer material in the extraction flange 18. The primer disc 26 is thereafter stamped a second time at step 104 to form the primer pocket 28 therein. Preferably, the primer pocket 28 is sized to receive a standard small rifle primer. The depth of the primer pocket 28 is therefore stamped to be less than a required height for a standard small rifle primer to account for the thickness 15 of polymer material forming the base end 14 during the subsequent molding step. Concurrently with formation of the primer pocket 28, the flash hole 30 is defined through the center of the pocket.

[0035] In some embodiments, such as the hybrid cartridge 40, step 104 may further involve stretching the flash hole 30 to form the flash hole extension 44. The flash hole extension 44 may simply be a hollow channel extending from the primer disc. Alternatively, the flash hole extension 44 may be a separate hollow tube, with an internal diameter substantially equal to the diameter of the flash hole 30, that is attached to the stamped primer disc 26.

[0036] Once the primer disc 26 has been formed in steps 102 to 104, the primer disc is suspended in a cartridge mold at step 106. Thereafter, the polymer body 12 is molded over the primer disc 26 in step 108. Molding of the polymer body 12 forms the base end 14 having an extraction flange 18 that encloses the primer disc 26. The outer dimensions and shape of the polymer body 12 are caliber dependent. In some embodiments, the molding step 108 may involve molding a straight-walled, bottleneck, or neckless ammunition configuration depending on the use requirements. The thickness 19 and thickness 15 is controlled during the molding step 108 to ensure sufficient polymer material is present to withstand the primer explosion and subsequent case extraction. Further during the molding step 108, polymer material will flow over the upper side 34 of the primer disc 26 to form the bottom surface 25 of the propellant chamber 24 and over the lower side 32 to form the base end 14. After the molding step is completed, the internal walls of the primer pocket 28 and the flash hole 30 are the only parts of the primer disc 26 that have exposed metal material.

[0037] The inventor has determined that the disclosed structure of the hybrid cartridge 10, particularly at the base end 14, substantially reduces the frequency of blowout occurrences. The metallic primer disc 26 forming the primer pocket 28 and flash hole 30 in combination with the controlled thickness 19 at the extraction flange 18 and thickness 15 in the base end 14 provides sufficient structural integrity to withstand the initial explosion from the primer upon firing of the cartridge. In particular, the inventor has determined that by using a standard small rifle primer in conjunction with the primer disc 26, the structural integrity of the base end 14 can be maintained without the need for expensive machined metal inserts to form the cartridge base. The thickness 19 of the polymer material in the extraction flange 18 further provides sufficient structural integrity for cartridge throughout the extraction process subsequent to firing. Thus, the hybrid cartridge according to the present invention can serve as a lightweight alternative to conventional brass cartridges without sacrificing the reliability of the cartridge.

[0038] Exemplary embodiments of the invention have been disclosed in an illustrative style. Accordingly, the terminology employed throughout should be read in a non-limiting manner. Although minor modifications to the teachings herein will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted, except in light of the appended claims and their equivalents.

Claims

1. A hybrid ammunition cartridge, comprising:a metal disc having a primer pocket formed in a first side of the disc and fluidically connected to a second side through a flash hole; anda polymer body molded over the metal disc from the first side to the second side, the polymer body forming an extraction flange around a perimeter of the metal disc and defining a polymer base end, a projectile opening formed in a distal end of the polymer body, and a propellant chamber formed between the polymer base end and the projectile opening.

2. The hybrid cartridge of claim 1, wherein the metal disc defines an outer diameter that is less than a maximum base diameter required by a standard cartridge of a caliber.

3. The hybrid cartridge of claim 2, wherein the extraction flange forms a second outer diameter that is substantially equal to the maximum base diameter for the standard cartridge.

4. The hybrid cartridge of claim 1, wherein the flash hole fluidically connects the primer pocket with the propellant chamber.

5. The hybrid cartridge of claim 1, wherein the flash hole comprises a diameter that is less than an internal diameter of the primer pocket.

6. The hybrid cartridge of claim 1, wherein the primer pocket is configured to receive a small rifle primer.

7. The hybrid cartridge of claim 1, wherein the polymer body further comprises an annular shoulder formed around the projectile opening.

8. The hybrid cartridge of claim 7, wherein the annular shoulder transitions into a neck.

9. The hybrid cartridge of claim 8, wherein the neck terminates in the projectile opening.

10. The hybrid cartridge of claim 1, wherein the first side of the metal disc comprises texturing.

11. The hybrid cartridge of claim 10, wherein the texturing is configured to increase surface adhesion between the metal disc and the polymer body.

12. The hybrid cartridge of claim 1, wherein the second side of the metal disc comprises texturing configured to increase surface adhesion between the metal disc and the polymer body.

13. The hybrid cartridge of claim 1, wherein the polymer body encloses the metal disc.

14. The hybrid cartridge of claim 13, wherein an internal surface of the primer pocket is metal.

15. The hybrid cartridge of claim 14, wherein an internal surface of the flash hole is metal.

16. A hybrid ammunition cartridge, comprising:a metal disc having a primer pocket formed in a first side and in fluid communication with a second side through an extended flash hole;a substantially cylindrical polymer body enclosing the metal disc to form a cartridge bottom having an extraction flange formed around a perimeter of the metal disc, a projectile opening formed in a distal end of the polymer body, and a propellant chamber formed between the metal disc and the projectile opening.

17. The hybrid cartridge of claim 16, wherein the extended flash hole extends a length into the propellant chamber.

18. The hybrid cartridge of claim 16, wherein the polymer body substantially covers the second side of the metal disc to form a polymer bottom surface in the propellant chamber.

19. The hybrid cartridge of claim 18, wherein the polymer body substantially covers the first side of the metal disc to form a polymer base end.

20. The hybrid cartridge of claim 16, wherein the polymer body further comprises an annular shoulder that transitions into a neck to form a bottleneck cartridge.

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