Patent Application
20250130025
The present invention relates generally to ammunition cartridges, and, more particularly, to an improved geometric design for a polymer ammunition cartridge nose.
Ammunition cartridges are traditionally formed from brass or some other metal, e.g., steel, aluminum, etc. While metallic cartridges are known to be relatively reliable, they are also heavy, expensive and potentially contain hazardous materials. Reliability and consistency in performance from round to round are key factors when selecting an ammunition cartridge to use.
One consideration for determining the reliability of an ammunition cartridge is ensuring the bullet pull is sufficient to withstand normal handling at all stages of the cartridge including transport, loading and firing. Bullet pull is understood in the art to mean the amount of force required to mechanically pull a bullet from its cartridge after it has been seated therein. Military specifications require a bullet pull value of at least 60 pounds of force. A proper bullet pull value ensures the bullet will not fall out or otherwise become dislodged from its seated depth in the cartridge throughout the life of that cartridge up until firing. If the bullet pull is too low, the bullet can easily dislodge during transport and handling, rending the cartridge ineffective. Even during the loading and firing of a cartridge with insufficient bullet pull, the bullet can become pushed back into the cartridge from the sheer force of firing the prior cartridge and chambering the cartridge with insufficient bullet pull. In conventional metallic cartridges, a distal end of the cartridge neck can be crimped or otherwise mechanically engaged to a bullet loaded therein for purposes of ensuring a sufficient bullet pull value, e.g., use of a cannelure.
In polymer ammunition, however, the problem of ensuring the right amount of bullet pull is more difficult than merely crimping the cartridge neck to the bullet due to the inherent properties of polymer materials. The prior art teaches the use of an adhesive around the inner diameter of a polymer cartridge neck to properly hold a bullet in place. However, due to the need for the maximum outer diameter of a bullet to be very closely matched to the inner diameter of a cartridge neck, application of the adhesive becomes difficult in and of itself. Prior art attempts to overcome this problem have taught using grooves formed in the length of the neck, e.g., Applicant's U.S. Pat. No. 9,835,423, or an annular ring formed at the projectile opening, e.g., U.S. Pat. No. 8,875,633, for receiving an adhesive to secure the bullet in the polymer cartridge. These prior art attempts, however, have been unsatisfactory and generated their own sets of problems thus failing to achieve the required reliability and consistency in performance from round to round.
Because polymer cartridges are inherently weaker than brass or other metallic cartridges, a problem can arise when the bullet pull value is too high. With too much bullet pull, polymer cartridges have been known to generate partial or complete tearing along a portion of the neck or rupturing in the cartridge body due to excess pressures building up in the cartridge caused by the bullet not being properly released. Examples of these cartridge failures can be seen in
A further problem known to occur in polymer ammunition using the prior art solutions is there can be an uneven release of the bullet from the cartridge. This can be caused by an uneven distribution of adhesive about the bullet diameter or from improper bullet seating in the cartridge. A significant decrease in the accuracy of the projectile results from such an uneven release because the projectile will nutate or wobble as it is released from the firearm barrel.
Thus, what is needed is a lightweight polymer cartridge that can generate sufficient and consistent bullet pull without decreasing the accuracy of the projectile or reducing the overall reliability in the cartridge.
The inventive concepts disclosed herein relate to an improvement in a polymer cartridge nose that overcomes numerous issues observed in prior polymer cartridge designs. The improved polymer cartridge nose has an engineered design that overcomes the problems of too little or too high bullet pull values and provides a consistent and reliable release of the bullet from the cartridge. The engineered solution of the improved polymer cartridge nose utilizes both mechanical engagement and adhesive bonding between the cartridge neck and a bullet installed therein to reliably and consistently produce a bullet pull value of at least 60 pounds of force.
In one embodiment according to the inventive concepts disclosed herein, there is a polymer ammunition cartridge that has a cartridge body extending from a base end and a cartridge nose extending from the cartridge body. The base end may be formed by a primer insert that is overmolded with the cartridge body. The cartridge nose includes a shoulder and a neck. The neck extends into a projectile opening defined at the distal end of the cartridge and configured to receive a projectile, e.g., a bullet. Defined on an inner surface of the nose and positioned at an intermediate location between the projectile opening and the shoulder is an annular shelf. At least one wicking groove is also defined on the inner surface of nose and extends from the projectile opening to the annular shelf. Preferably, there is a plurality of wicking grooves formed on the inner surface of the neck and extending from the projectile opening to the annular shelf. The wicking grooves are designed to receive adhesive after a bullet has been installed in the cartridge. The annular shelf is designed to arrest the flow of the adhesive so that the length of bondage between the bullet and the cartridge neck is limited to the wicking grooves. In preferred embodiments, the wicking grooves and the adhesive generate a bullet pull value of at least 60 pounds of force. The inner diameter of the neck between the shoulder and the annular shelf can be substantially uniform. Further, that portion of the neck between the shoulder and the annular shelf can be designed to generate frictional engagement with a bullet installed in the cartridge. The mechanical engagement generated between this portion of the neck and the bullet also contributes to the creation of a consistent and reliable bullet pull value.
In some embodiments, the plurality of wicking grooves are substantially radially symmetrical about the inner surface of the neck. The wicking grooves can be formed parallel to the longitudinal axis of the cartridge. Further, the length of each wicking groove can be substantially equal to the length of every other wicking groove. Alternatively, the longitudinal length of some wicking grooves may be different than the longitudinal length of other wicking grooves.
In more elaborate embodiments of the invention, the cartridge nose can further comprise an annular groove formed in the neck. The annular groove is preferably formed between the projectile opening and the annular shelf. At least one of the wicking grooves connects to the annular groove to provide a common flow path for adhesive introduced to the nose. Preferably, each of the plurality of wicking grooves are connected to the annular groove.
In some embodiments of the invention, the cartridge can be formed as a two-piece cartridge which includes a primer insert that is overmolded with the cartridge body that is integrally formed with the cartridge nose. Alternatively, the cartridge nose and the cartridge body can be molded as distinct pieces that are thereafter secured together during an assembly process.
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 increased resistance to partial or complete case tearing. The disclosed polymer cartridge has an engineered cartridge nose that consistently creates the desired bullet pull value. Thus, the disclosed polymer cartridge achieves a similar level of reliability and consistency in performance as metallic equivalents without the downside of being heavy, expensive and potentially toxic.
Throughout the disclosure, certain terms may be used to more easily and clearly define the claimed invention. These terms are not meant to be limiting but merely for the purpose of describing the invention in a clear and concise manner. Thus, as used herein, proximal and/or distal may be used to describe the general orientation of a cartridge when it is loaded into a firearm chamber. Thus, the skilled artisan will readily understand that a distal end would refer to the bullet receiving end, e.g., the projectile opening 32, of a cartridge and a proximal end refers to the primer receiving end, e.g., the base end 16, of the cartridge.
The neck 30 of the polymer cartridge 10 extends into a projectile opening 32 defined at the distal end of the neck. The projectile opening 32 is configured to receive a projectile, e.g., a bullet, during the assembly process of the polymer cartridge 10. Formed on the inner surface of the neck 30 is an annular shelf 34. The annular shelf 34 is formed at an intermediate location between the projectile opening 32 and the shoulder 26 to provide a physical barrier for limiting flow of an adhesive applied to the inner surface of the neck 30. At least one wicking groove 36 is also formed on the inner surface of the neck 30 and extends from the projectile opening 32 to the annular shelf 34. Preferably, there is a plurality of wicking grooves 36 formed about the inner surface of the neck 30. The wicking grooves 36 terminate at the annular shelf 34 to define a flow path for an adhesive that is applied at the projectile opening 32 after a bullet has been installed into the polymer cartridge 10. The annular shelf 34 is designed to stop the flow of adhesive at the shelf, thereby limiting the bonded area to the length of the wicking grooves 36. The combination of the annular shelf 34 and one or more wicking grooves 36 focuses the bonded area between a bullet and the neck 30 of the cartridge 10 to significantly reduce the occurrence of cartridge failures or the unwanted dislodgment of the bullet from its seated depth. Further, the combination of features allows a manufacturer to readily and reliably select the desired bullet pull value by controlling the placement of the annular shelf 34 to thereby control the amount of bonded area between the bullet and the one or more wicking grooves 36.
Thus, by controlling the bonded surface area between the neck 30 and the bullet 38 and introducing the annular shelf 34 to stop the flow of adhesive, the problem of too high of bondage between the bullet and the cartridge has been alleviated. This has resulted in a significant increase in the reliability of the polymer cartridge 10 by reducing the frequency of partial and complete case tearing during live-fire events. Further, by controlling the number and dimensions of the wicking grooves 36, the problem of too low a bullet pull value is avoided and the polymer cartridge 10 can be consistently produced with the desired bullet pull value.
At least one of the wicking grooves 36 is integrally connected to the annular groove 46 to define a common flow path for adhesive to flow from the projectile opening down the wicking grooves into the annular groove. Preferably, each of the wicking grooves 36 connects with the annular groove 46 to form a flow path from each wicking groove to the annular groove. The wicking grooves 36 and the annular groove 46 can combine to provide an area of bondage with the bullet that circumvolves the outer diameter of the bullet at the annular groove 46 and extends longitudinally along the outer diameter of the bullet corresponding to the length of each wicking groove 36. Regardless of the embodiment, after the bullet has been installed in the polymer cartridge 10, the annular shelf 34 provides a structural blockage of the adhesive thereat and mechanical engagement with the bullet 38 there below by causing diametric interference between the bullet 38 and the remainder of the neck 30 to the shoulder 26.
The total number of wicking grooves 36 and the specific dimensions for each individual wicking groove 36, i.e., length, depth and width, can vary depending on the manufacturer's specific need. For instance,
Throughout this disclosure, the terms “polymer” and “synthetic polymer” and “synthetic coating” shall be interpreted in a non-limiting fashion and given a broad interpretation according to their plain and ordinary meaning. “Polymer” can mean a natural polymer or a synthetic polymer, and any invention described herein that refers to a “synthetic polymer” may, in an alternative embodiment, substitute a natural polymer for the synthetic polymer and vice versa. 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 inventive concepts disclosed herein can be applied to virtually all ammunition cartridges of any caliber or size, including rifle and pistol ammunition cartridges as well as large caliber artillery rounds. Further, the disclosed inventive concepts apply equally to cartridges designed for military and civilian use.
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.
