Reduced Tension Cartridge Case with Two-Stage Neck

This application is a continuation of U.S. Non-provisional patent application Ser. No. 18/298,808, filed Apr. 11, 2023, which claims the benefit of U.S. Provisional Patent Application No. 63/329,870, filed Apr. 11, 2022, both entitled REDUCED TENSION CARTRIDGE CASE WITH TWO-STAGE NECK. The entire contents of both applications are hereby incorporated by reference herein.

The present invention is directed to ammunition cartridge casing modifications for improving performance.

In an ammunition cartridge for a firearm, a casing holds a projectile (e.g., a bullet). Retention force is the amount of force that would be necessary to pull the projectile from the casing. Cartridge design may impact cartridge parameters such as retention force, shelf-life, durability, and/or manufacturing processes along with ballistic performance such as reliability, accuracy, and/or muzzle energy, among other aspects.

A cartridge for a firearm comprises a projectile and a case. The case comprises a base configured to hold a primer, a body extending from a first end adjacent the base to a second end, and a two-stage neck adjacent the second end of the body and configured to retain the projectile, the two-stage neck comprising a neck length, an interior, and an exterior. The interior of the two-stage neck comprises an interference band that is adjacent the second end of the body and comprises an interference diameter extending an interference length along the two-stage neck, the interference band configured to provide an interference fit with the projectile resulting in an interference retention force. The interior of the two-stage neck also comprising a clearance band comprising a clearance diameter and extending a clearance length along the two-stage neck, the clearance diameter being greater than the interference diameter, the clearance band configured to provide an interference fit with the projectile resulting in a clearance retention force, and a transition portion located between and adjoining the interference band and the clearance band. The interference retention force is greater than the clearance retention force, both the interference band and the clearance band are at least partially coextensive with the projectile, and one or more of the interference length and the clearance length comprise about 25% or more of the two-stage neck length.

The above summary of the various representative embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices of the invention. The Figures in the detailed description that follow more particularly exemplify these embodiments.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been depicted by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Relevant to all of the figures disclosed herein, certain features of the present invention may be exaggerated for clarity and illustrative purposes only. Generally, many applicable standard cartridges have an exterior neck diameter less than 0.5000″, including diameters as low as of 0.220″ or less. Some embodiments of the present disclosure relate to modifications to the interior and/or exterior diameter of a cartridge neck, such as, for example, modifications that are in the range of approximately 0.0001″-0.0010″. As such, the modifications may be difficult to see with the naked eye and/or inside the range of conventional manufacturing tolerances. As one example,exaggerates the relative diameters of an interference bandand a clearance band, whereasshows the same view with relative diameters that are closer to the actual scale of one embodiment of the present disclosure.

Referring to, embodiments of the present disclosure are directed to a cartridgeof firearm ammunition (projectile not shown) comprising a casethat includes a bodyextending from a first endto a second endalong a central axis. The bodyof the casemay have an exterior diameterand an interior diameter. A two-stage neckof the caseis adjacent the second endof the bodyand is designed to hold a projectile(not shown, see). In some embodiments the two-stage neckhas a reduced diameter relative to the bodyand the casecomprises a shoulderbetween the two-stage neckand the second endof the case. In embodiments, the casecomprises a baseat the first end. The basemay hold a primer in a primer hole. The casemay be formed of various materials such as conventional brass or higher-strength metals such as steel, steel alloys, steel-boron alloys, aluminum, and the like, as discussed further below.

Referring also to, one embodiment of the two-stage neckextends from the shoulderto a terminal edgeto define an overall neck lengthand comprises an interiorand an exterior. In certain embodiments, the stages of the two-stage neckare comprised of an interference bandand a clearance bandwith a transitionbetween. In embodiments, the interference bandand the clearance bandare formed on both the interiorand the exteriorof the two-stage neck. In other embodiments, the interference bandand the clearance bandare formed only on the interiorwhile the exteriorprovides a cylindrical or substantially cylindrical shape with a substantially consistent outer diameter along the neck lengththat does not mirror corresponding changes in the inner diameter.

In certain embodiments, the interference bandcomprises an interference diameterof an interior surfaceand extends for an interference lengthalong the two-stage neck. An exterior surfaceof the interference bandcomprises an exterior diameter. In some embodiments, the interference bandmay provide an interference fit when the projectileengages the interior surfaceto be positively held in the case, resulting in an interference retention force. In these embodiments, the interference bandis at least partially coextensive with the projectileand is not positioned entirely behind the projectile when the projectile is seated in the case.

The design of the interference bandmay be tuned to a desired interference retention force that precludes or reduces the need for crimping after the projectileis seated. In other words, the number of crimps and/or the degree of crimping may be reduced or eliminated for any one or more crimps along the two-stage neckand/or at the terminal edge. For example, the interference retention force may be tuned by changing the interference length, the interference diameter, selecting a case material with different rigidity, changing the thickness of the two-stage neckat the interference band, changing the angle of the interference bandto be an increasing or decreasing diameter towards the clearance band, changing geometry of the clearance band, or the like.

In some embodiments, the interference retention force may be increased by one or more crimps (not shown) pressing the interference bandradially inwardly into the projectileand/or pressing the clearance bandradially inwardly into the projectile (for example, a mouth crimp). However, as discussed further below, other embodiments of the present disclosure provide a desired retention force without the need for any crimping, interfitting parts, or the like.

In some embodiments, the clearance bandcomprises a clearance diameterof an interior surfaceand extends a clearance lengthalong the two-stage neck. In certain embodiments, the clearance diameter is greater than the interference diameter. An exterior surfaceof the clearance bandcomprises an exterior diameter. In various embodiments, the clearance bandmay provide different fits with a projectileincluding an interference fit with the clearance diameterless than the projectile diameter and providing some retention force, a line-to-line fit with the clearance diametersubstantially equal to the projectile diameter and providing minimal retention force relative to the retention force provided by the interference band, or a clearance fit with the interior surfaceradially spaced from the projectile.

The fit of the clearance bandwith the projectileresults in a clearance retention force. In embodiments with a clearance fit, the clearance retention force may be 0%, or substantially zero percent, or about 0%-5%, about 5%-15%, about 15%-25%, about 25%-35%, about 35%-45%, about 45%-55%, about 55%-65%, about 65%-75%, about 75%-85%, between 85%-75%, and ranges therebetween. In any disclosed embodiments, the clearance bandis at least partially coextensive with the projectile when the projectile is seated in the case, in order to provide the fit and other benefits disclosed herein; therefore, the clearance band is not positioned entirely behind or in front of the projectilewhen the projectile is seated in the case.

In certain embodiments, the two-stage neckmay provide an overall retention force on a projectilethat may be either a combination of the clearance and interference retention forces or may be equivalent to the interference retention force alone. In some embodiments, the interference retention force constitutes the entire or substantially the entire overall retention force of the two-stage neckon the projectile. In some embodiments, the clearance diameteris greater than or equal to the interference diameterand the clearance retention force is less than the interference retention force. In certain embodiments, the clearance diameter is greater than the interference diameter by a range of about 0.0001-0.0050″, about 0.0001-0.0040″, about 0.0001-0.0030″, about 0.0001-0.0020″, about 0.0001-0.0010″, about 0.0001-0.0005″, and ranges therebetween. In embodiments, the interior surfaceof the clearance band(or the entire interiorof the two-stage neck) comprises clearance portions that have a diameter greater than the interference diameter, for example axially-extending grooves, concave dimples, or the like, resulting in the clearance bandproviding relatively less contact with the projectilethan the interference bandor a conventional neck of the same material. In embodiments, the clearance bandcomprises a material with lower strength and/or rigidity than a material that comprises the interference band.

The neck lengthis a combination of the interference lengthand the clearance lengthand also may include a length of the transitionand/or a mouthif present. In embodiments, the interference lengthcomprises about 10% of the neck length; in other embodiments, the interference length comprises about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, or about 75% of the neck length, and ranges that include combinations of any such interference lengths. As such, in embodiments, the clearance lengthcomprises about 90% of the neck length; in other embodiments, the clearance length comprises about 85%, about 80%, about 75%, about 70%, about 65%, about 60%, about 55%, about 50%, about 45%, about 40%, about 35%, about 30%, or about 25% of the neck length, and ranges that include combinations of any such clearance lengths. In another sense, embodiments of the present disclosure provide both the interference lengthand the clearance lengthcomprising at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, and at least 40% of the neck length, and ranges that include combinations of any such lengths. In still another sense, embodiments of the present disclose provide one or more of the interference lengthand the clearance lengthcomprising about 10-90%, about 15-85%, about 20-80%, about 25-75%, about 30-70%, or about 35-65% of the neck length. In one embodiment, a two-stage neckcomprises a neck lengthof about 0.300″ and the interference lengthis about 15% or about 0.050″ and the clearance lengthis about 85% or about 0.250″.

It will be appreciated that the disclosed embodiments of the interference bandare distinct from a conventional crimp, an abutting seat, other retention enhancements, or other incidental features of a case. A conventional case crimp forms a projection in an interior neck surface toward the projectile, but the interior neck surface then continues on both sides of the crimp at a consistent diameter. Therefore a crimp necessarily has two transitions: one inward from the surface and one outward back to the surface. By contrast, embodiments of the present disclosure provide only a single transitionbetween surfaces of different diameters. Additionally, in certain embodiments, the projectiledoes not have any complementary features or shapes relative to the transitionand is not penetrated by, and does not otherwise mirror, the transition.

Referring to the embodiment illustrated in, the interference bandis positioned interior or rearward of the clearance band. The interference bandin embodiments without a shoulderextends from the second endof the bodyof the caseto the clearance band. In embodiments with a shoulder, the interference bandextends from the end of the shoulder to the clearance band. In certain embodiments, the exteriorof the two-stage neckcomprises the exterior diameterat the clearance bandbeing greater than the exterior diameterat the interference band. In other embodiments such asdiscussed below, the exterior diameterat the clearance bandis equal to or substantially equal to the exterior diameterat the interference band.

In, embodiments of the interior and exterior surfaces of the interference and clearance bands,are substantially straight walls when viewed in cross-section, extending parallel to the central axis. In some embodiments, the interior surfaceof the clearance bandis substantially cylindrical; in other words, the clearance diameteris substantially consistent along the clearance bandto the terminal edgeof the two-stage neck. In certain embodiments, the interior surfaceof the interference bandis substantially cylindrical; in other words, the interference diameteris substantially consistent along the interference band. In other embodiments, one or more of the interior surfaces,and/or exterior surfaces,may have other shapes, such as curved, concave or convex, and also tapering toward the terminal edge, and tapering toward the bodyof the case, or combinations thereof.

Referring to, in various embodiments, features of the two-stage neckmay be rearranged or modified without departing from the scope of the present disclosure. Aspects of any of the disclosed embodiments may be combined or omitted while still providing the benefits of the two-stage neck.

Referring to, in certain embodiments the two-stage neckcomprises an interiorthat is the same as, but the exteriorand exterior surfacemay be substantially cylindrical along the entire neck lengthand does not change in diameter from the interference bandto the clearance band. In other words, the exterior diameterof the interference bandis substantially the same as the exterior diameterof the clearance band.

Referring to, in some embodiments the two-stage neckcomprises reversed positions for interference bandand the clearance band. The interference bandcomprises the terminal edgeand extends to the transitionat the interference diameter. The clearance bandextends from a transitionto the shoulder(or to the second endof the body) at the clearance diameter. To form the two-stage neck, the steps for forming the clearance bandmay be performed by reaching through the case, for example from the base.

Referring to, in some embodiments a two-stage neckis similar toand further includes a mouthformed in a clearance band, the mouth flares radially outwardly to an interior mouth diameter. In some embodiments, the mouth diameteris about 101-110% of the clearance band interior diameter, in certain embodiments the mouth diameteris about 0.0005-0.0100″ greater than the clearance band interior diameter. In certain embodiments, the mouthcomprises the terminal edge. In embodiments, the mouthis flared along both interior and exterior sides.

In embodiments such as, the clearance bandcomprises the mouth. Because the clearance bandalready provides an increased interior diameter (e.g., clearance diameter), the mouthdoes not need to flare outwardly as far as with conventional necks.

As shown inand applicable to any embodiments, a projectileis mounted in the two-stage neck,, the projectile comprising an ogive portionhaving an ogive length, a mid portionhaving a mid length, and a rear portionhaving a rear length. The projectilecomprises an exterior surface, a portion of which engages the two-stage neck,at least at the interference band.

In certain embodiments, the interior diameter (e.g., interference diameter) of the interference bandis the same as or less than the diameter of the projectile, causing the interference fit. Interference fit, as used herein, is known term of art, sometimes also referred to as press fits and/or shrink fits, referring to a traditional method for joining cylindrical parts. Generally, in an interference fit, the inner part, such as a shaft, bearing, bushing, or in our case a projectile, is machined to be bigger (e.g., have a larger width, diameter, etc.) than the mating opening (e.g., interference diameter) of the outer part, such as a housing, or casing. The larger part is then forced (e.g., pressed) into the smaller part, causing both parts deform slightly and fit together. This method of joining creates extremely high friction between two parts (e.g., larger part and smaller part) that can withstand large amounts of torque without separation of the parts.

In certain embodiments, the interference diameteris about 0.0010″ less than the projectile diameter, more generally about 0.0005″-0.0015″, more generally the interference diameteris smaller than the projectile diameter by about 0.0020″ or less. In some embodiments, the clearance bandis at least partially coextensive with the ogive portion, thereby accommodating a longer ogive lengththan would otherwise fit in a conventional neck having only the interference diameter.

In any of the disclosed embodiments, at least a portion of the projectileis coextensive with both the interference bandand the clearance band,. In certain embodiments, the projectileis not in contact with the clearance band,(i.e., clearance fit). In embodiments, the projectilecomprises the exterior surfacethat does not conform in shape to the clearance band,. In other embodiments, the exterior surface partially conforms to the clearance band,and/or the transition, but does not touch the entire lengthof clearance band.

In certain embodiments, the mouthis spaced from the exterior surfaceof the projectileto form a mouth gap. In such embodiments, a sealantmay be provided between the mouthand the projectile. Applicable sealants include UV-cured sealants, or anaerobic sealants, other wicking sealants, or other waterproofing sealants, and any other sealant used for this purpose in the cartridge field.

In embodiments with a clearance fit for the clearance band,, a radial gapis formed between the interior surfaceof the clearance bandand the exterior surfaceof the projectile. In certain embodiments, the radial gap is about 0.001-0.005″. In embodiments with or without a mouth, a sealant may be provided at the radial gapbetween the clearance band,and the projectilein the same manner as sealant.

Referring to, various embodiments with different arrangements of the transitionbetween the interference bandand the clearance bandare shown, with the remainder of the two-stage neckbeing substantially similar. Instead of the step shape of,shows a transitionthat is a curve between the bands.shows a transitionthat is a gradient angled between the bands. The transitionis illustrated as angled at about 45 degrees, but may be at any angle between 0 and 90 degrees.

In some embodiments, the cartridgeconforms to standardized dimensions, for example dimensions established by the Sporting Arms and Ammunition Manufacturers' Institute, Inc. (SAAMI). The standardized dimensions cover both a cartridge and corresponding firearm with acceptable tolerance ranges, for example a neck diameter and a chamber diameter. It will be appreciated that embodiments of the two-stage neckof the present disclosure will provide the exterior clearance diameterthat is less than the smallest possible chamber diameter of the tolerance range for a given standardized cartridge. Accordingly, in embodiments, the caseis configured for a cartridge of standardized cartridge dimensions comprising a predetermined projectile diameter and the interference diameterof the interference bandis less than the predetermined projectile diameter and the clearance diameterof the clearance bandis slightly less than, equal to, or greater than the predetermined projectile diameter, but the exterior diameterof the clearance bandmust remain smaller than the chamber diameter. As one example, the SAAMI specifications for a 308 Winchester include maximum cartridge neck diameter of 0.3435″ at the mouth while the minimum chamber diameter is 0.3442″ at the mouth, therefore corresponding clearance bandwill have an exterior diameterthat must be less than 0.3442″ but may be greater than 0.3435″. In embodiments, the neck lengthremains in conformance with the standardized cartridge dimensions.

Embodiments of the present disclose provide a method for forming a case(e.g., an ammunition case). In embodiments, the method comprises drawing and forming a body, a base at one end of the body, and a neck at an opposite end of the body, the neck comprising: a neck length extending from the body to a terminal edge, an exterior surface, and an interior surface comprising an interference diameter; and increasing the interior surface of the neck to form a clearance band comprising a clearance diameter greater than the interference diameter, wherein the expanding is performed along about 15% to about 85% of the neck length.

In certain embodiments, the increasing step is performed by punching the neck with a die. For example, after the neck is formed with an inner diameter equal to the interference diameter, a punch having an outer diameter equal to the clearance diameteris driven axially into the neck. The depth of the punch provides the clearance lengthof the clearance band. In other embodiments, the increasing step is performed by boring out the two-stage neckin the desired location of the clearance band.

Case materials applicable to the present disclosure include metals and non-metals. Some embodiments of the caseare formed from a high-strength metal such as brass, steel, steel alloys, steel-boron alloys, high-strength aluminum, and the like. In embodiments, the caseis formed of a steel-boron alloy comprising about 0.001%-0.500% boron by weight, other steel-boron alloys comprise less than about 0.500% boron by weight, less than about 0.400% boron by weight, less than about 0.300% boron by weight, less than about 0.200% boron by weight, less than about 0.100% boron by weight, about 0.001-0.100%, about 0.001-0.050%, about 0.001-0.010%, and about 0.001-0.005%. Various other case materials are also contemplated herein, such as, for example, as disclosed in U.S. Patent Application Publication No. 2022/0097124, filed Sep. 24, 2021, entitled BORON STEEL HIGH-PRESSURE CARTRIDGE CASE, which is hereby incorporated by reference herein in its entirety.

In some embodiments, relative to a conventional brass case, the greater rigidity and modulus of elasticity in high-strength metals may provide functional benefits but may also have a significant impact on retention force. Many conventional arrangements of a cylindrical neck for a brass case rifle cartridge yield retention forces that are less than or equal to about 150 pounds of force (lbf), whereas a steel alloy case with the same design (including the same neck design) can yield retention forces that are 3-4× greater and significantly higher muzzle energy. By contrast, embodiments of the present disclosure provide the benefits of a high-strength case with comparable retention force to brass. In embodiments of the present disclose comprising a caseformed of a high-strength metal, e.g., steel or boron-steel, the two-stage neckprovides a retention force comparable to brass, in particular a retention force of about 25-150 lbf on the projectile, less than or equal to about 150 lbf, less than or equal to about 200 lbf, or less than or equal to about 250 lbf.

The disclosed embodiments may be beneficial for using steel or other relatively high-strength materials for the casewith retention forces that are comparable to brass. Such high-strength case materials may offer strength, cost, and manufacturability benefits as compared to conventional configurations and materials, particularly for modem military applications. Nonetheless, applicable embodiments of case materials also include brass or other relatively low-strength materials.

As discussed above, in certain embodiments, the clearance bandmay preclude the need for a mouthor reduce the amount of mouth flare required for proper assembly and seating of the projectile. This may provide various benefits, such as utilizing less ductile metals and/or simpler manufacturing processes. In a similar manner, the design of the interference bandmay be tuned to a desired interference retention force that precludes or reduces the need for crimping after the projectile is seated. Because forming a mouth and/or crimp strain the metallic material and damage the integrity of the surface (for example, a plated surface), embodiments of the present disclose provide improved surface integrity for the interior and exterior surfaces of the two-stage neck. As a result, the two-stage neckmay be less susceptible to corrosion than conventional designs, which may obviate the need for costly material choices or corrosion mitigation manufacturing steps.

Various modifications to the above examples are contemplated to be within the scope of the present disclosure. The various angled or curved surfaces of the transition, interior surfaceof the clearance band, mouthmay be varied without departing from the scope of the disclosure. The casemay have various modifications in the body, shoulder, and/or base.

Embodiments of the present disclosure are applicable to various types, sizes, and uses of ammunition cartridges. For example, the two-stage neckmay be implemented for casings of typical military cartridges such as 5.56 mm NATO, 6.5 mm, 6.8 mm, 7.62 mm NATO, 338 cal., and .50 BMG. In embodiments, projectiles may be lead, lead-free, jacketed, or non-jacketed. The present disclosure may also be applicable to centerfire as well as rimfire cartridges, as well as various types of firearms including handguns, rifles, semiautomatics, automatics, combinations thereof, and the like. Applicable rifles may include match, sporting, and shotgun styles.

All of the features disclosed, claimed, and incorporated by reference herein, and all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is an example only of a generic series of equivalent or similar features. Inventive aspects of this disclosure are not restricted to the details of the foregoing embodiments, but rather extend to any novel embodiment, or any novel combination of embodiments, of the features presented in this disclosure, and to any novel embodiment, or any novel combination of embodiments, of the steps of any method or process so disclosed.

Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose could be substituted for the specific examples disclosed. This application is intended to cover adaptations or variations of the present subject matter. Therefore, it is intended that the invention be defined by the attached claims and their legal equivalents, as well as the illustrative aspects. The above described embodiments are merely descriptive of its principles and are not to be considered limiting. Further modifications of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the inventive aspects.