Patent Application
20250003719
The present invention relates generally to ammunition cartridges, and, more particularly, to polymer ammunition cartridges having an improved geometric fitment in an industry standard firearm chamber.
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 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 .50 caliber brass ammunition cartridges plus links can weigh about 35 pounds (100 brass cartridges plus links). Military personnel and vehicles, especially winged and rotary vehicles such as fighter jets or helicopters, are therefore limited in the quantity of cartridges they can carry due to the significant weight of these cartridges when considered en masse.
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.
A key consideration for shooters in deciding which cartridge to use is the reliability of the cartridge and its consistency in terms of firing. This is especially important when considering military uses where a failed cartridge could literally be the difference between life and death. In terms of polymer cartridges, several aspects of the cartridge have yet to meet the reliability and consistency standards set by conventional metallic cartridges.
A problem found to occur in previous attempts at polymer ammunition cartridges is that the cartridges would experience partial or complete tearing along a portion of the cartridge body. These tears could be found at the base end where mechanical forces are exerted on the cartridge during extraction from a firearm after being fired. Also, tears can be found to occur at or along a portion of the cartridge neck. For instance,
The neck portion of polymer cartridges is highly susceptible to partial or complete tearing due to polymer being inherently weaker than brass equivalents and this particular portion of the cartridge being relatively thin. Further, as is common with most ammunition cartridges, adhesive can be applied at the bullet-neck interface to ensure the bullet is secured within the cartridge. The addition of the adhesive to a polymer cartridge neck can cause increased resistance to bullet release upon firing, further increasing the likelihood the cartridge will partially or completely tear in the neck area.
Thus, what is needed is a lightweight polymer ammunition cartridge that resists partial or complete tearing of the cartridge during firing and extraction from a firearm while attaining reliability and consistency from cartridge to cartridge.
The inventive concepts disclosed herein relate generally to an improved polymer cartridge and methods associated with making such improved cartridge. The improved polymer cartridge is considered to be “non-standard” with industry standards for legacy metallic cartridges of the same caliber. The improved polymer cartridge exhibits a geometric design engineered to cause interference at specific points of contact in an industry standard chamber. Cartridges designed according to the inventive concepts disclosed herein exhibit a significant increase in reliability during firing. This means the improved polymer cartridge can be reliably chambered in an industry standard firearm chamber, with no need to modify the existing chamber, and fired at high rates with significantly diminished rates of failure.
In one embodiment according to the present invention, an improved polymer-based ammunition cartridge is disclosed. The improved polymer cartridge is designed to be used with existing firearms having a chamber with internal chamber dimensions that are compliant with industry standards for a firearm chamber of the specified caliber of cartridge. The improved polymer cartridge includes a primer insert engaged to a cartridge body to define a base end. The cartridge body extends forward from the primer insert to a shoulder region. The axial length of the cartridge body from the base end to the shoulder region is compliant with industry standards for the corresponding length in an industry standard cartridge of the specified caliber.
A cartridge nose extends from the shoulder region and includes a first angle dictated by industry standards for the specified caliber of cartridge and a neck. The neck is integrally connected to the first angle by an interference region that is noncompliant with industry standards for the specified caliber of cartridge. The interference region is engineered to cause interference between a shoulder formed by the first angle and a corresponding shoulder support surface in the industry standard chamber for the specified caliber of cartridge.
In one embodiment, the interference region can be configured as a second angle which transitions the first angle to the neck. In some embodiments, the second angle can be between 15 to 25 degrees and preferably is 20 degrees. In alternate embodiments for some ammunition cartridges types, such as a 6.5 mm Creedmoor, the second angle may be larger than 25 degrees and is sufficient to cause the engineered interference between the first angle and the corresponding shoulder support surface of the industry standard chamber for that caliber of cartridge.
In further alternate embodiments, the interference region can be configured as a 0.5% to 5% increase in the axial length of the improved cartridge defined from the base end to a proximal end of the neck beyond a corresponding industry standard length for the specified caliber of cartridge. Preferably, the interference region is a 2% increase in the axial length from the base end to the proximal end of the neck beyond the industry standard axial length for the specified caliber of cartridge.
In further embodiments, the improved polymer cartridge can include a second interference region formed at the distal end of the neck. The second interference region is configured to cause axial interference between the distal end of the neck and a chamber-bore interface in the industry standard firearm chamber. The second interference region can be formed as a result of a 0.5% to 5% increase in the overall axial cartridge length defined from the base end to the distal end of the neck beyond a corresponding industry standard axial cartridge length for the specified caliber of cartridge. In preferred embodiments, the second interference region is formed as a result of a 2% increase in the overall axial cartridge length.
In exemplary embodiments, the specified caliber of cartridge is a 308 Winchester cartridge, and the improved polymer cartridge is an improved, polymer-based 308 Winchester cartridge.
A method for manufacturing the improved polymer cartridge is also disclosed. The method involves molding a polymer cartridge over a primer insert. The primer insert defines the base end of the cartridge. The molded polymer cartridge comprises a cartridge body and a cartridge nose. The polymer cartridge may be molded as one piece where the cartridge body and the cartridge nose are integrally formed together in a single step. Alternatively, the polymer cartridge may be molded as two-pieces, where the cartridge body is first molded over the primer insert and has a forward coupling region. The cartridge nose is thereafter molded and secured to the coupling region. Thus, the improved polymer cartridge can be molded as a two-piece cartridge (primer insert plus polymer cartridge) or a three-piece cartridge (primer insert plus polymer cartridge body plus polymer cartridge nose).
The cartridge body is molded such that it has a length defined from the base end to a shoulder region that is compliant with industry standards for the caliber of cartridge. The cartridge nose is molded having a first angle which is compliant with industry standards for an outer shoulder angle. The cartridge nose is further molded to have a neck which is integrally connected with the first angle by an interference region. The interference region is noncompliant with industry standards and is configured to cause interference between the cartridge shoulder formed by the first angle and a corresponding shoulder support surface in the industry standard firearm chamber for the specified caliber of cartridge.
In one embodiment, molding the interference region can include molding a second angle which transitions the industry compliant first angle into the neck. The second angle can be molded to be between 15 degrees to 25 degrees and preferably is molded to be about 20 degrees. However, in some embodiments and depending on the specific caliber of ammunition cartridge being molded, the second angle may be molded with an angle higher than 25 degrees. In alternate embodiments, the molding of the interference region can include molding the axial length of the improved cartridge, defined from the base end to the proximal end of the neck, to be 0.5% to 5% longer than a corresponding axial length in an industry standard cartridge for the specified caliber of cartridge. In preferred embodiments, the improved polymer cartridge is molded such that the axial length to the proximal end of the neck is 2% longer than the corresponding industry standard axial length for the specified caliber of cartridge.
In a more elaborate embodiment, the method can further include molding the improved polymer cartridge with a second interference region at the most distal end of the neck. The second interference region is configured to cause axial interference between the distal end of the neck and the chamber-bore interface in the industry standard firearm chamber for the specified caliber of cartridge. Molding the second interference region can include molding the overall axial length defined from the base end to the distal end of the neck to be between 0.5% to 5% longer than the corresponding axial length of the industry standard cartridge for the specified caliber.
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:
The following disclosure presents exemplary embodiments of a polymer ammunition cartridge which has improved characteristics of reliability and resistance to partial or complete tearing. The improved polymer cartridge can be reliably chambered and fired from firearms that have dimensions compliant with the industry standards.
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.
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. 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”).
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.
The four lengths, L1CART, L2CART, L3CART, L4CART and the outer shoulder angle α represent the maximum dimensions that an industry standard 308 Winchester cartridge 10 may possess to be compatible with a firearm chamber having the minimum industry standard dimensions, for instance as shown in
Due to the inherent variability in the manufacturing process of legacy metallic cartridges, e.g., the industry standard 308 Winchester cartridge 10, these maximum dimensions are rarely achieved, and it is more likely that a conventional industry standard cartridge 10 is kept under these maximum dimensions. This is to ensure any variability in dimensions will not result in a cartridge that exceeds the maximum industry standard dimensions for the specific caliber, which would cause the cartridge to be noncompatible with a corresponding industry standard firearm. Thus, in industry standard legacy metallic cartridges, e.g., 308 Winchester cartridge 10, there is a wide tolerance band that is not compatible with polymer-based ammunition cartridges. Due to the inherent weakness of polymer when compared to legacy metals used for ammunition cartridges, the inventors have discovered that polymer-based cartridges require additional contact support in a firearm chamber to ensure the cartridge does not fail upon firing and the subsequent extraction of the fired cartridge from the firearm chamber.
Table 1 below is a summary of the maximum industry standard 308 Winchester cartridge 10 dimensions described above and the minimum industry standard 0.308 chamber 30.
The industry standard 308 Winchester cartridge 10 is conventionally formed from brass or other legacy metallic materials that are relatively rigid and do not deform easily. For this reason, the industry standard maximum dimensions of a cartridge and the minimum dimensions of the corresponding chamber must be tightly controlled and closely matched. As can be seen from Table 1 above, the chamber has a larger overall minimum required length L4CHAM when compared to the maximum overall length of the cartridge L4CART, i.e., 2.049″>2.015″. This ensures an industry standard cartridge 10 will fit within the industry standard chamber 30 and does not become jammed at the chamber-bore interface. Further, the diameter DCHAM is larger than the corresponding cartridge diameter DCART in the cartridge 10 to ensure the shoulder 22 does not become jammed in the firearm chamber during or after firing.
The improved polymer cartridge 100 can be molded as a two-piece cartridge having the primer insert 110 overmolded with the cartridge, which includes the cartridge body 114 and the cartridge nose 116 molded as a single piece. Alternatively, the improved polymer cartridge can be molded as a three-piece cartridge where the cartridge body 114 is first molded over the primer insert 110 to the shoulder region 108. Thereafter, the cartridge nose 116 is molded to extend forward from the cartridge body 114. The cartridge body 114 engages with the cartridge nose 116 at a shoulder joint 122 (
The improved polymer cartridge 100 has a primer insert 110 defining a base end 102 of the cartridge. The cartridge body 114 is preferably molded over the primer insert 102 to ensure a secured and reliable connection that resists tearing at the base end 102 during extraction from the chamber 30. The cartridge body 114 extends forward from the base end 102 to a shoulder region 108. The shoulder region 108 transitions into a cartridge nose 116 which includes the shoulder 118 and the neck 106 connected by an interference region 112. The interference region 112 is engineered to cause interference between the shoulder 118 and the corresponding shoulder support surface 36 in an industry standard chamber 30. Because of the inherent pliability of the polymer used to make the improved polymer cartridge 100, the shoulder 118 is able to be compressed against the corresponding shoulder support surface 36 sufficiently to fit within the industry standard chamber 30 without causing structural damage to the cartridge 100 or to the chamber 30. Further, the compression of the shoulder 118 due to the inclusion of the interference region 112 does not cause the firearm to jam because the remaining dimensions remain compliant with industry standards, as is detailed further below. The engineered support in the improved polymer cartridge 100 caused by the interference region 112 resulting in the compression effect in the chamber 30 significantly reduces the occurrence of partial or complete cartridge tearing during firing or extraction thereafter.
Inclusion of the interference region 112 in the improved polymer cartridge 100 increases the axial length of several discrete sections of the cartridge when compared to an industry standard cartridge, e.g., the industry standard 308 Winchester cartridge 10 described above, while keeping other sections consistent with industry standards. For instance, a first length L1IMP defined from the base end 102 to the shoulder region 108 is compliant with industry standards for the specified caliber of cartridge. (Note, “IMP” designates “improved.”) Thus, the cartridge body 114 is compliant with an industry standard cartridge body 11. Further, the diameter of the cartridge body 114 is maintained in a 0.2 to 1.1% diametric clearance with regard to an industry standard chamber 30. Maintaining the first length L1IMP in compliance with industry standards and the diameter in a 0.2 to 1.1% diametric clearance ensures the improved polymer cartridge 100 does not become jammed in the industry standard chamber 30.
The shoulder 118 has an industry standard outer shoulder angle, e.g., 40 degrees for a standard 308 Winchester cartridge. The interference region 112 can be a second angle that transitions the shoulder 118 into the neck 106. For example, the interference region 112 can be configured as a radial transition angle of 15 to 25 degrees which transitions the outer shoulder angle of 40 degrees into the neck 106. In alternative embodiments, the interference region 112 can be configured as a radial transition angle larger than 25 degrees, depending on the angle of the industry standard outer shoulder angle. Preferably, the interference region has an angle of about 20 degrees transitioning the first angle defined by the shoulder 118 to the neck 106.
In an alternative embodiment, the interference region 112 can be an extension of the shoulder 118 such that the total length L3IMP from the base end 102 to the proximal end of the neck 106 is longer than the equivalent length L3CART in an industry standard cartridge, e.g., the 308 Winchester cartridge 10 described above. For instance, in the above example of the industry standard 308 Winchester cartridge 10, the length L3CART is a maximum of 1.712 inches whereas a corresponding length L3IMP in the improved polymer cartridge 100 can be 0.5% to 5% longer in axial length. The increase in the axial length of L3IMP in the improved polymer cartridge 100 is configured to generate interference between the shoulder 118 and a corresponding shoulder support surface 36 in an industry standard chamber 30.
The improved polymer cartridge 100 can have a second interference region 120 defined at the distal end 104 of the neck 106. The second interference region 120 is configured to cause axial interference between the distal end 104 of the neck 106 and the chamber-bore interface 40 of the industry standard chamber 30. To ensure that the improved polymer cartridge 100 can be properly chambered in an industry standard chamber 30 without becoming jammed, the neck 106 maintains a diametrical clearance of 0.3% to 5% within a corresponding internal neck support surface 39 of an industry standard chamber 30, i.e., the outer diameter of the neck 106 will be about 0.3% to 5% less than the inner diameter of the internal neck-support surface 39 of the chamber 30 to maintain diametrical clearance. Again, due to the inherent pliability of the polymer cartridge 100, the second interference region 120 is able to sufficiently compress, in the axially direction, in the industry standard chamber 30 so as to not cause a cartridge jam or structural failure of the cartridge in the chamber. The second interference region 120 can be formed as a result of a 0.5% to 5% increase in axial length L4IMP beyond the length L4CART in the industry standard cartridge 10. For instance, in the above example of the 308 Winchester cartridge 10, the industry standard length L4CART is a maximum of 2.015 inches and the length L4IMP of the improved polymer cartridge 100 could be 0.5% to 5% longer in axial length due to the inclusion of the second interference region 120, e.g., increased to about 2.025 inches to 2.116 inches in overall axial length.
Similarly, the second interference region 120 is represented by the second overlap 202 between the distal end 104 of the neck 106 and the chamber-bore interface 40. Again, in use, the distal end 104 of the neck 106 will compress at the second interference region 120 against the chamber-bore interface 40 due to the inherent pliability of polymer. The neck 106 of the improved polymer cartridge 100 operates in a 0.3% to 5% diametric clearance within the neck support surface 39 of the chamber 30.
The cartridge nose 116 of the improved polymer cartridge 100 can also have a second interference region 120 defined at the distal end 104 of the neck 106. The second interference region 120 can come as a result of a 0.5% to 5% increase in the overall axial length L4IMP in comparison to length L4CART of an industry standard cartridge 10 of the same caliber. The increase in overall axial length L4IMP causes engineered axial interference at the second interference region 120 between the distal end 104 of the neck 106 and the chamber-bore interface 40 in an industry standard chamber 30.
Alternatively, the improved polymer cartridge may be molded in a three-piece design. In such a process, the cartridge body 114 may first be molded over the primer insert 110 to define a length from the base end 102 to the shoulder region 108. The distal end of the shoulder region 108 is molded with a shoulder joint 122. Thereafter, the noncompliant cartridge nose 116 is molded at step 308 to securely connect to with the shoulder joint 122. An adhesive may be added to the shoulder joint 122 prior to molding of the noncompliant cartridge nose thereto. Alternatively, the noncompliant cartridge nose 116 may be welded to the shoulder joint 122 or any other conventional means for reliably securing two polymer components together may be used.
After the improved polymer cartridge 100 is molded over the primer insert 110, the cartridge is removed from the mold at step 310. Thereafter, a primer is loaded into the primer insert at step 312. Next, at step 314, the internal propellant chamber defined within the improved polymer cartridge 100 is filled with propellant of a selected charge. In the final step 316, a projectile is loaded and secured into the improved polymer cartridge 100 through the open distal end 104 of the neck 106.
In field testing of cartridges formed according to principles of the invention disclosed herein, the results of the improved polymer cartridge 100 revealed a significant increase in reliability during firing and an unexpected decrease in the frequency of partial or complete cartridge tearing. For instance, a polymer-based 308 Winchester cartridge complying with the maximum industry standard dimensions for a legacy metallic 308 Winchester cartridge, e.g., cartridge 10 above, would experience significant rates of failure due to partial or complete tearing of the cartridge across the cartridge body or in the cartridge nose. Examples of these failures can be seen in
The present inventors have thus determined that to achieve the same levels of reliability and consistency as established by the counterpart legacy metallic cartridges, polymer cartridges must be manufactured with certain dimensions that deviate from the set industry standards for that specific cartridge. By controlling the deviation of these dimensions with certain tolerance ranges beyond the maximum dimensions set by industry standards, the reliability of the improved polymer cartridge 100 was significantly increased while maintaining interoperability with existing weapons platforms.
The method steps detailed above have been described in stepwise fashion, however, the skilled artisan will realize that many of the molding steps can be accomplished simultaneously in a conventional injection molding process. The above detailed steps should therefore be read in a non-limiting fashion and are meant merely for descriptive purposes. Further, 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 filler.
While the disclosure herein has provided primary examples of the inventive concepts applied to an improved 308 Winchester polymer cartridge, this is meant for descriptive purposes only and should not be interpreted as limiting the inventive concepts. The inventive concepts disclosed throughout this disclosure can be readily applied to any conventional civilian or military cartridge for small, medium and large sized calibers.
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.
