SMALL ARMS CARTRIDGE

Abstract

Provided is a centerfire rifle cartridge. A case has a head end, an open mouth end for receiving a projectile, and a central axis. The head end has a base portion substantially conforming to that of a .50 BMG cartridge. The case has a case wall with a taper of up to 1.0 relative to the central axis. A frusto-conical shoulder portion extends from the case wall and has an angle of approximately 40 relative to the central axis. A neck portion extends from the shoulder portion and has a mouth sized to receive a .375 caliber (9.5 mm) projectile.

Claims

1. A centerfire rifle cartridge, comprising: a case having a head end, an open mouth end for receiving a projectile, a central axis, and an axial length measured along the central axis, the head end having a base portion up to 0.804 inches in diameter; the case having a case wall, the case wall having a taper of 0.85 to 1.0 relative to the central axis, a frusto-conical shoulder portion extending from the case wall and having an angle of 35 to 45 relative to the central axis, and a neck portion extending from the shoulder portion; and the neck portion having a mouth sized to receive a .375 caliber projectile.

2. The cartridge of claim 1, wherein the case has a total axial length in the range of about 3.24 inches to about 3.29 inches.

3. The cartridge of claim 1, wherein the wall has an axial length from the head end of about 2.50 inches.

4. The cartridge of claim 1, wherein the case wall taper is about 0.9 relative to the central axis.

5. The cartridge of claim 1, wherein the case capacity is greater than 200 grains H.sub.2O.

6. The cartridge of claim 5, wherein the case has a capacity in the range of about 210-230 grains H.sub.2O.

7. The cartridge of claim 1, further comprising a projectile having a weight in the range of about 350-410 grains

8. The cartridge of claim 7, wherein the loaded overall length is at least 4.65 inches.

9. The cartridge of claim 8, wherein the loaded overall length is about 4.825 inches.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Like reference numerals are used to indicate like parts throughout the various drawing figures, wherein:

[0020] FIG. 1 is a side elevation view of a cartridge with seated bullet according to an embodiment of the invention, partially cut away to show cross-section of base and case wall;

[0021] FIG. 2 is a side view thereof showing dimensional specifications thereof;

[0022] FIG. 3 is a chamber reamer specification drawing (not to scale) for the cartridge embodiment; and

[0023] FIG. 4 is a side view of a projectile according to an embodiment of the invention.

DETAILED DESCRIPTION

[0024] With reference to the drawing figures, this section describes particular embodiments and their detailed construction and operation. Throughout the specification, reference to one embodiment, an embodiment, or some embodiments means that a particular described feature, structure, or characteristic may be included in at least one embodiment. Thus, appearances of the phrases in one embodiment, in an embodiment, or in some embodiments in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the described features, structures, and characteristics may be combined in any suitable manner in one or more embodiments. In view of the disclosure herein, those skilled in the art will recognize that the various embodiments can be practiced without one or more of the specific details or with other methods, components, materials, or the like. In some instances, well-known structures, materials, or operations are not shown or not described in detail to avoid obscuring aspects of the embodiments.

[0025] Referring first to FIG. 1, therein is shown a firearm cartridge 10 according to one embodiment of the present invention. As found in all fixed ammunition, the cartridge 10 is generally symmetrical around a central axis and comprises a case 12, which provides generally cylindrical walls 14 axially extending from a base portion 16. The base portion 16 includes an annular exterior grove 18 that defines a rim 20 for extraction according to well-known means from a firearm chamber. The base portion 16 includes a primer pocket 22 formed in the head 24 of the base portion 16. The primer pocket 22 is connected through a flash hole 26 to a propellant-holding powder chamber 28 defined between the walls 14 of the case 12. Axially spaced from the base portion 16, the case walls 14 include a frusto-conical shoulder portion 30 at which the diameter of the case 12 is significantly reduced and transitions into a neck portion 32. The neck portion 32 holds or seats a projectile (bullet) 34.

[0026] Referring now to FIG. 2, dimensional aspects of this embodiment of the cartridge 10 are shown. The cartridge case 12 and seated projectile 34 are substantially symmetric about their longitudinal axis a. The projectile 34 for this embodiment is a .375 caliber solid bullet, which will be described in greater detail below. The case 12 includes a base portion 16 with dimensions consistent with those of a .50 BMG cartridge (and those of a .416 Barrett cartridge). The .416 Barrett case may be used as the parent for the case 12 of the present invention. Likewise, the .416 Barrett is derived from the case of a .50 BMG cartridge. Thus, all dimensions associated with the base portion 16 of the case 12 may be substantially the same as these other rounds. The case 12 is significantly shorter than that of the .50 BMG and differs significantly from those of the .416 Barrett. Specifically, the angle of the shoulder portion 30 is significantly steeper at about 40. The transition zones between the case wall 14, shoulder portion 30, and neck portion 32 may be formed with a somewhat rounded radius according to the Ackley improved specifications. However, unlike a full Ackley improved modification, which generally removes any taper from the case wall 14 to maximize powder capacity, the cartridge 10 of the present invention retains a cartridge wall taper of up to 1, with the preferred taper being at about 0.9. The neck can be shortened, but the full length allows better adjustment of seating depths for projectiles. As will be discussed in greater detail below, the primer pocket 22 is sized to receive a .50 BMG-size primer. As previously described, the 40 shoulder angle reduces material flow of the case 12, when fired, and, as will be discussed in greater detail below, affects the propellant burn rate, chamber pressure, and projectile velocity.

[0027] Referring now also to FIG. 3, therein is shown a specification drawing for a chamber reamer to receiver the cartridge 10 of this embodiment in a barrel having a nominal .375 caliber bore. Note that the drawing of FIG. 3 is a schematic representation of dimensions and is not illustrated to scale. When a cartridge 10 according to this embodiment of the invention is fired in a chamber formed according to the reamer specifications shown in FIG. 3, the case 12 will be expanded (fire formed) by the internal pressure of the burning propellant and may force the above-described rounded transitions at the shoulder portion 30 into the more sharply defined dimensions of the barrel chamber. According to well-known methods, a previously fired case 12 may be resized to original specifications and reloaded.

[0028] Projectiles are commercially available in .375 caliber having a weight as low as 350 grains or as high as 452 grains. Of course, heavier projectiles have a higher ballistic coefficient, but require greater energy to achieve muzzle velocities necessary to maintain supersonic speed and stability for greater distances. A variety of .375 caliber projectiles 34, typically machined from solid copper and having a mass in the range of 350 to 400 grains, or above, may be utilized with successful results. Three example projectiles are described in greater detail below.

Example 1

[0029] A Flat Line .375 caliber bullet made by Warner Tool Company of North Swanzey, N.H., provides a 361 grain, solid copper bullet having a 2.20 inch overall length (OAL). This projectile includes a 16 boat tail and may be made in accordance with the invention described in U.S. Patent Application Publication No. 2016/0327380, published Nov. 10, 2016, the contents of which are hereby incorporated herein by reference. This projectile has ballistic coefficients (BC) acoustically measured in the range of 3,000 to 15,000 fps of G1BC=0.980 and G7BC=0.494. Ballistic coefficients measured by Doppler radar chronograph of G1BC=0.961 and G7BC=0.480. The minimum twist recommended for this projectile is 1:10 inches. The inventors have found a preferred twist rate of 1:8.65 inches to 1:8.75 inches. This example is illustrated in FIG. 4.

Example 2

[0030] A non-standard 400 grain, .375 caliber, solid copper bullet made by Berger Bullets LLC of Fullerton, Calif. Sample projectiles have a calculated BC greater than 1.0 (about 1.1). Warner Tool Company, referenced above, also makes a 400 grain, .375 caliber projectile that is suitable.

Example 3

[0031] A MTAC (match/tactical) 3.745/.3655 caliber, 402 grain, solid copper projectile made by Cutting Edge Machining Solutions Inc., d/b/a Cutting Edge Bullets, of Drifting, Pa., having a G1BC=0.990 and OAL of 2.209 inches. This projectile requires a twist of 1:7.5 inches or faster.

[0032] A primer (well-known, not shown) sized to seat in a primer pocket 22 configured for .50 BMG-size primers may be used. The geometry of the case 12 of the present invention provides maximum performance using a medium-slow burning powder, generally in the category of those designed for the .338 Lapua Magnum or .50 BMG cartridges. H50BMG or similar powders may be used. A powder designed for the .338 Lapua Magnum cartridge having a burn rate only slightly faster than powder intended for .50 BMG cartridge may provide better performance. For example, 168 grains of Reloder 33 propellant powder by Alliant Powder of Anoka, Minn., has been used in the cartridge 10 of the present invention to propel a 361 grain projectile through a 34 inch barrel to an average muzzle velocity in the range of 3,150 to 3,200 fps. As previously described, the burn rate of propellant powders has been found to be different than predicted by the powder manufactures. Likewise, performance of the cartridge has been found to be different than predicted due to the novel case geometries and projectile caliber combinations.

[0033] The cartridge 10 is accommodated by a 50 BMG-class action and bolt, the case 12 having substantially the same base and head dimensions of a .50 BMG cartridge and a shorter OAL. Chamber pressures produced are within ranges safely accommodated by a 50 BMG-class action, bolt, and barrel.

[0034] As described above, unexpected performance has been produced using a 34 inch barrel in .375 caliber. The performance has been found to mimic that of the calculated performance of a projectile weighing 20% less. Using this adjusted performance calculation, it is expected that a 361 grain projectile could exceed 3,300 fps from a 38 inch barrel. Using a twist rate of 1:8.65 inches, the projectile stays supersonic past 3,000 yards, with the expectation of targetable flight to at least 5,000 yards.

[0035] While one or more embodiments of the present invention have been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. Therefore, the foregoing is intended only to be illustrative of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not intended to limit the invention to the exact construction and operation shown and described. Accordingly, all suitable modifications and equivalents may be included and considered to fall within the scope of the invention, defined by the following claim or claims.