Patent Application
20250137762
The invention disclosed herein relates generally to polymer-based ammunition cartridges, and more particularly to improved neck designs for polymer-based ammunition cartridges and bullets engineered to be loaded into the improved neck.
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 0.50 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 selecting the ammunition cartridge to use is the reliability of the cartridge and its consistency in terms of firing the bullet. These factors are especially important for military use purposes where even small inconsistencies in cartridge performance can be the difference between life and death for the soldier.
Many factors are known to have impacts on the reliability and consistency of performance for ammunition cartridges. One of these factors is known as the bullet-pull value, which is the amount of force required to pull a bullet from a cartridge after it has been properly seated therein. The bullet-pull value must be high enough to ensure the bullet does not become dislodged or otherwise moved from its seated position during routine transport and handling. Further, a sufficient bullet-pull value allows the buildup of internal pressure in the cartridge after firing to ensure a firearm's recoil mechanism will function properly prior to the bullet being released from the cartridge. Another of these factors is the concentric release of the bullet from the cartridge upon reaching the required internal pressure threshold thereof. An uneven or non-concentric release of the bullet from the cartridge can cause a significant decrease in the overall accuracy of the bullet by misaligning the bullet tip from the flightpath thereby increasing the tilt or yaw of the bullet during flight. In some instances, the increased yaw can be self-corrected during flight by the spin imparted on the bullet from the rifling of the firearm barrel. However, the overall accuracy of such bullet is diminished in comparison to a concentrically released bullet, all other factors remaining the same.
In brass and other conventional metallic ammunition cartridges, the above discussed factors can be accounted for by implementing a cannelure and crimp at the mouth of the cartridge. Conventionally, a bullet can have an annular groove formed in the outer surface thereof. The bullet is thereafter seated in the cartridge so that the cannelure or groove is aligned with the distal end of the neck, i.e., the mouth. The metallic cartridge mouth is thereafter crimped so that the cartridge engages the cannelure on the bullet. This action can create the desired bullet-pull value while also ensuring the bullet will be concentrically released from the cartridge. Furthermore, use of a bullet cannelure along with the crimping action can ensure the bullet is seated at the same depth for each cartridge made. However, due to the inherent frangibility of polymer once formed, the same bullet structure and crimping action has been unsatisfactory in polymer-based ammunition cartridges.
Thus, what is needed is a polymer-based ammunition cartridge that can produce a consistent, desired bullet-pull value while ensuring consistent bullet seating depth from round to round, resulting in a consistent concentric release of the bullet from the cartridge.
The invention disclosed herein relates to polymer-based ammunition cartridges and specially designed bullets to be fired therefrom. The polymer cartridges disclosed herein provide a consistent bullet-pull value from round to round. Further, the combination of the specially designed bullet with the disclosed polymer cartridges results in the same depth of bullet seating from round to round of the disclosed cartridge. Methods for manufacturing the disclosed polymer cartridges are also disclosed.
In some embodiments, the invention is a polymer-based ammunition cartridge that has an insert defining the base end and a cartridge body extending forward from the insert. A primer pocket and flash hole are defined through the insert. A powder chamber, enclosed by the cartridge body, is in fluid communication with the primer pocket via the flash hole. A nose extends forward from the body, opposite the insert. The nose includes a shoulder transitioning into a neck that defines a projectile aperture. At least one annular ridge is formed about the inner surface of neck. The annular ridge is formed at an intermediate location, along the neck, between the shoulder and the projectile aperture. The annular ridge is designed to frictionally engage the outer surface of a bullet configured to be loaded into the cartridge.
In some embodiments, the annular ridge forms a seal between the neck and the projectile loaded therein. The bullet preferably has a groove designed to matingly engage the annular ridge of the cartridge. In preferred embodiments, engagement of the bullet with the annular ridge generates a bullet-pull force of at least 45 pounds per square inch. The diameter defined by the annular ridge is preferably less than the maximum diameter of the bullet to be loaded into the cartridge.
Alternative embodiments of the polymer cartridge may include a second annular ridge formed about the inner surface of the neck. The second annular ridge is preferably positioned between the shoulder and the first annular ridge. The first and second annular ridges may be of different heights, depending on the embodiment. A bullet having two cannelures positioned at a height corresponding to the location of the two annular ridges can be loaded into the polymer cartridge. The two annular ridges are configured to concentrically align the bullet in the neck.
In some embodiments, the polymer cartridge is formed as a two piece cartridge where the body and the nose are integrally formed together as a single piece. The body and nose are thereafter molded over the insert to form the two-piece cartridge. Alternatively, the polymer cartridge can be formed as a three-piece cartridge that includes the insert overmolded by the body and the nose engaged to the body at a shoulder joint.
The shape and dimensions of the annular ridge may be dependent on the caliber the polymer cartridge is designed for and the desired terminal performance for the bullet loaded therein. In some embodiments, the annular ridge may be configured as a semi-spherical bulge about the inner surface of the neck. Alternatively, the annular ridge may have opposing sidewalls connected by a flat top surface to define a rectangular profile.
In further embodiments, the invention relates to the nose for a polymer-based ammunition cartridge. The nose has a shoulder which transitions into a neck that forms a projectile opening at the distal end thereof. A shoulder joint is formed opposite the projectile opening. The shoulder joint is configured to matingly engage with the body portion of a polymer cartridge. An annular ridge is formed about the inner surface of the neck between the projectile opening and the shoulder. The annular ridge is configured to engage the outer surface of a bullet configured to be loaded into the nose, once fully assembled. The nose may further include a second annular ridge formed about the inner neck surface between the shoulder and the first annular ridge. The nose may further include a cartridge body engaged to the shoulder joint and an insert engaged to the body opposite the shoulder joint to form an assembled polymer-based ammunition cartridge.
The invention disclosed herein further includes a bullet engineered to engage the polymer cartridge. The bullet has a body that extends between the base end and the tip end. The forward end of the body may taper inwardly toward the longitudinal centerline to define an ogive extending to the tip end. The bullet includes an annular groove formed in the outer surface of the body. The annular groove is configured to engage an annular ridge formed about the inner surface of a polymer cartridge neck between the projectile opening and the shoulder. In some embodiments, the bullet may include a second annular groove formed in the outer surface and configured to engage a second annular ridge about the inner surface of the polymer cartridge neck. The annular grooves on the bullet are positioned at a height corresponding to the location of the annular ridge in the cartridge neck. A bullet seated in the polymer cartridge to a depth sufficient for engagement between the groove and the ridge will define a total axial length of the ammunition round that is within the acceptable range for total axial length as determined by the caliber of cartridge and weapons platform being used.
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 ammunition cartridges and methods for making cartridges that have a consistent bullet-pull value and ensure the even release of a bullet from the cartridge mouth upon firing. Various bullets engineered to engage and be fired from the disclosed ammunition cartridge are also disclosed. In particular, various embodiments of polymer-based ammunition cartridges are disclosed. The polymer-based ammunition cartridges have an engineered neck design that will provide consistent bullet seating depth from round to round. Further, polymer cartridges according to the present invention have a consistent bullet-pull value from round to round and provide for the even discharge of the bullet from the cartridge mouth. These and other aspects of the invention will become apparent in light of the following disclosure.
Note, 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.
The inventive concepts disclosed herein can be applied to virtually any caliber of ammunition, including small and medium calibers for rifles and pistols. Further, the inventive concepts disclosed herein can be applied to certain types of larger caliber ammunition, including large artillery ammunition. Thus, the following disclosure is meant for illustrative purposes only and should be interpreted in a nonlimiting fashion.
The polymer cartridge 10 further includes a nose 32 extending from the forward end 34 of the body 12. In some embodiments, the nose 32 and the body 12 can be molded as a single molded piece. Alternatively, the nose 32 may be molded separate from the body 12 and thereafter secured to the body forward end 34 during an assembly process. In such embodiments, a shoulder joint 36 is formed where the nose 32 engages the body forward end 34. In some embodiments, the shoulder joint 36 is designed as a half-lap joint where each of the joined parts comprises 50% the total thickness of the joined parts. In some alternative embodiments, each of the joined pieces can taper in opposite directions to form the total thickness of the joined pieces. An adhesive may be applied to the shoulder joint 36 during the assembly process to strengthen the bond of the nose 32 to the body 12.
The nose 32 has a shoulder 38 which transitions into a neck 40. The distal end of the neck 40 is open to define a projectile aperture 42. The projectile aperture 42 is configured to frictionally engage a bullet of a certain caliber which the polymer cartridge 10 is designed to fire. The exact diameter of the projectile aperture 42 therefore is dependent upon the caliber of bullet and the caliber of the polymer cartridge 10. Formed between the projectile aperture 42 and the shoulder is an annular ridge 44. The annular ridge 44 is formed about the inner surface 46 of the neck 40 and projects inwards. The annular ridge 44 is configured to engage the outer surface of a projectile, such as a bullet 47. In preferred embodiments, the annular ridge 44 is formed at a specific position of the neck 40, between the projectile aperture 42 and shoulder 38. A bullet 47 engineered to be fired from the polymer cartridge 10 includes an outer groove or cannelure 48 at a location corresponding to the location of the annular ridge 44 of the polymer cartridge 10. Engagement of the annular ridge 44 with the cannelure 48 of the bullet 46 is designed to ensure that each round of polymer cartridge 10 has the bullet 47 seated therein to the same depth. Further, the annular ridge 44 is engineered to strengthen the frictional engagement of the bullet 47 in the neck 40 to ensure the desired bullet-pull value is generated consistently from round to round.
Conventional bullets designed with a traditional cannelure placement for brass or other metallic cartridges cannot be used with the disclosed polymer cartridge 10 because the location of the cannelure will not match the location of the annular ridge 44. The overall axial length of a given cartridge plus the projectile loaded therein is limited to the total axial length of the chamber for which that cartridge is designed to be fired from. These dimensions must be tightly controlled to ensure the ammunition cartridge of a given caliber can be safely loaded into a firearm of that caliber, regardless of the manufacturer of either the cartridge or firearm. In brass and other metal cartridges, the bullet is designed so that the mouth of the metal cartridge can be crimped to engage the cannelure. The malleability of the metals used in conventional cartridges allows for the crimping action to be applied thereto without risking any structural damage to the cartridge. To ensure the overall length is within the acceptable range for a given caliber, the cannelure is positioned at a location along the bullet to allow the bullet to be seated at to a depth that aligns the cannelure with the mouth while staying within the required overall axial length. The exact cannelure location may vary among projectiles for a given caliber depending on the specific design of that projectile, e.g., longer projectiles require deeper seating in the cartridge to stay within the required overall axial length for that caliber and therefore the cannelure may be placed closer to bullet tip versus the base of the bullet. However, the cannelure placement on the projectile remains such that the cartridge mouth can be crimped to engage the cannelure. The location of a cannelure is measured in terms of its height above the base end of the bullet.
Conventional bullets therefore have an improper cannelure placement for engagement with the annular ridge 44. Seating a conventional bullet to a depth sufficient for the cannelure to engage the annular ridge 44 will result in the overall axial length of the polymer cartridge 10 plus the bullet being outside the acceptable range for a given caliber of cartridge, e.g., bullet will be seated deeper in the neck 40 resulting in a shortening of the overall axial length outside the acceptable range. The bullet 47 therefore is engineered with a cannelure 48 positioned to engage the annular ridge 44 at an intermediate position of the neck 40 to maintain the overall axial length of the polymer cartridge 10 within the required specifications for a given caliber of cartridge.
The annular ridge 44 renders the crimping action obsolete in the polymer cartridge 10. The height of the annular ridge 44 will be substantially equal to the depth of the cannelure 48 so that the bullet 46 will be frictionally held in the neck 40 at the appropriate depth. Engagement between the annular ridge 44 and the cannelure 48 of the bullet 46 preferably generates a bullet-pull force of at least 60 pounds per square inch (psi). In some embodiments of the polymer cartridge 10, the bullet-pull force generated can be increased beyond 60 psi by altering the relative dimensions of the annular ridge 44 and corresponding cannelure 48. Alternatively, adhesive may be introduced at the projectile aperture 42, after the bullet 46 has been loaded therein, to further strengthen the engagement between the bullet 47 and the neck 40. Adhesive may flow between the inner surface 46 of the neck 40 and the outer surface of the bullet 47 until reaching the annular ridge 44, which will act as a stop to prevent adhesive from reaching the powder column below in the powder chamber 26.
The exact dimensions of the annular ridge 44 are dependent upon the caliber of polymer cartridge 10 and the desired performance of the bullet to be fired therefrom. In some preferred embodiments of small and medium sized caliber polymer cartridges 10, the annular ridge 44 may have a height of between about 0.001 inches to about 0.100 inches, more preferably between about 0.005 inches to about 0.010 inches. As used with reference to the annular ridge 44, the “height” of the ridge is measured as the distance the ridge extends inwards off the inner surface 46 of the neck 40. Larger caliber ammunition cartridges, such as some artillery rounds, may require an annular ridge 44 with a height substantially larger than 0.100 inches due to the increased projectile size and higher pressures generated during firing of the round.
The nose 50 with two annular ridges 52, 54 offers several advantages over the nose 32 with a single annular ridge 44. For instance, engagement of the bullet 56 with the two annular ridges 52, 54 may produce a sufficient amount of friction to generate a bullet-pull value of at least 60 psi. In such scenarios, there would no longer be a need to apply adhesive to the projectile opening 42 since the friction generated is sufficient to create the required bullet-pull value. However, an adhesive or other type of sealant may still be applied for other purposes, such as waterproofing the cartridge 10. The two annular ridges 52, 54 will also aid in the concentric alignment of the bullet 56 in the nose 50, which will increase accuracy of the polymer cartridge 10 from round to round.
In some embodiments, the first annular ridge 52 and the second annular ridge 54 may be of different heights. For instance, the first annular ridge 52 may have a height that is less than the height of the second annular ridge 54. A bullet 56 being loaded into the nose 50 will more easily pass over the shorter first annular ridge 52 thereby reducing occurrences of misalignment or structural damage to the nose during the assembly process. Further, shortening the first annular ridge 52 will ensure a smooth release of the bullet 56 from the nose 50 once sufficient pressure has been built up in the powder chamber 26 to overcome the friction generated by the second annular ridge 54 engaged to cannelure 57. The shorter first annular ridge 52 will have a minimal impact on the trajectory of the bullet 56 as it passes over the first annular ridge 52 upon release from the nose 50.
The nose 60 has similar advantages over the nose 32 as described above with regard to nose 50. The three-ridged design of nose 60 provides for a more concentric alignment of the bullet 67 in the nose and may also render the use of an adhesive unnecessary to generate the desired bullet-pull value. An adhesive or other type of sealant may still be applied to the nose 60 for other purposes such as waterproofing the polymer cartridge 10, as described above. In some embodiments, each of the three annular ridges 62, 64, 66 may be of different heights or may all be the same height. In embodiments having different heights, the first annular ridge 62 may be the “shortest” with the second annular ridge 64 having slightly more height and the third ridge 66 being the tallest. Similar to nose 50, the stepwise increase in the height of each respective annular ridge 62, 64, 66 allows for sufficient pressure buildup in the powder chamber 26 prior to release of the bullet 67 from the nose 60. The shorter ridges 62 and 64 will allow the bullet 67 to readily pass over them with minimal disruption to flight trajectory.
The two-ridged nose 50 and the three-ridged nose 60 may be particularly useful with some types of elongated bullets that are required to be seated deeper into the cartridge 10 to maintain an acceptable overall axial length for the given caliber. Typically, an elongated bullet has an elongated ogive extending to the tip at the forward end. To maintain an acceptable total axial length, these bullets are commonly seated deeper into the cartridge. However, the two-ridged nose 50 and the three-ridged nose 60 can be used with a bullet of conventional length for the caliber so long as the cannelures location coincides with the annular ridges in the cartridge 10.
In preferred embodiments, the polymer cartridge 10 is molded as a three-piece cartridge, including the body 12 molded over the insert 14 to form the base end. The nose 32 is molded separately from the body 12 and thereafter attached to the forward end 34 at the shoulder joint 36. An adhesive may be applied to the shoulder joint 36 to increase the bondage strength at the joint. The annular ridge 44 (or multiple annular ridges, depending on the embodiment) may be formed concurrently during the molding of the nose 32, along with the other features of the nose. Alternatively, the annular ridge 44 may be formed after the polymer cartridge 10 has been molded and assembled. In such case, a grooved dowel may be inserted into neck 40, where the location of the groove on the dowel corresponds to the desired annular ridge. A press ring is thereafter applied over the outer surface of the nose 32 and force is applied. The force applied by the press ring will force excess polymer material from the neck 40 into the groove on the dowel to form the annular ridge 44. In some embodiments, heat may be applied prior to compression of the press ring or may be applied throughout the compression step.
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.
