AU2018256609B2 - Small arms cartridge - Google Patents

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 (9.5mm) projectile. 4/4 34 COMPOUND CURVE OGIVE CZ) CN 0.371 0.3752 0 r- 0.29512 - - 16 BOAT TAIL FIG. 4

Description

4/4

34

COMPOUND CURVE OGIVE CZ) CN

0.371

0.3752

0

r-

0.29512 - -

16 BOAT TAIL

FIG. 4

SMALL ARMS CARTRIDGE

Technical Field

[0001] This invention relates to a firearm cartridge and barrel chamber for it.

More particularly, it relates to a cartridge and cartridge load combination for efficient,

high-velocity, long-range, precision shooting.

Background

[0002] Ballistics, the science and study of projectiles and firearms, may be

divided into three categories. These are: interior ballistics, exterior ballistics, and

terminal ballistics. Interior ballistics relates to the propulsion of a projectile, through

the bore of a barrel, to achieve a determined velocity as it leaves the muzzle of the

barrel. Exterior ballistics relates to the flight of the projectile and how that flight is

affected by its shape, its velocity, and external forces, including wind and gravity.

Terminal ballistics relates to what effect the projectile has on the target it strikes.

[0003] A projectile may be selected for the desired effect on its intended target

and the range it must travel from the firearm to engage the target. One of the most

critical factors on external ballistic performance is the ballistic coefficient (BC) of the

projectile. The BC of a bullet is a measure of its ability to overcome air resistance in

flight. The drag coefficient of a particular bullet shape and mass will vary depending

on its velocity. Propelling a bullet with a high BC at the highest achievable velocity

will provide the best exterior ballistics performance, i.e., the "flattest" trajectory, for

long range shooting. Muzzle velocity is determined by interior ballistics performance.

[0004] An ammunition cartridge "load" is a combination of the selected

cartridge case, powder propellant charge, primer, and projectile (or bullet). The

performance of a cartridge load is determined by the combination of the shape and size of the cartridge case, the powder propellant used (including burn rate and pressure), and the size, shape, and mass of the projectile. Once a projectile has been selected, several parameters influence the interior ballistics of an ammunition load. The shape and dimensions of the cartridge shell or case (relative to the interior bore dimensions of the gun chamber), the amount and characteristics of the propellant (powder) charge, the primer, and the primer vent connection to the main cartridge chamber, and barrel length are primary aspects of interior ballistics performance, for a projectile of a given mass, that determine muzzle velocity.

Pressure and head space parameters are also important, and they must be balanced

against the other parameters.

[0005] The cartridge case is a hollow cylinder with a head end and a

projectile-receiving end. In "bottle-necked" cartridges, the cylinder includes a

generally cylindrical body portion extending from the head end to a frusto-conical

shoulder. The body portion has a central opening in the head end for a primer and

an annular cartridge extraction groove formed adjacent the head end. The frusto

conical shoulder is integrally formed with the body and tapers from the body portion

to a generally cylindrical integrally formed neck portion. The neck portion extends

longitudinally from the shoulder portion and has a diameter smaller than the diameter

of the body portion with an open mouth for receiving and holding the projectile.

[0006] While cartridge cases or shells theoretically may have any combination

of dimensions, there are several reasons why cartridges are limited in their

dimensions. The characteristics of gun powder and structural limitations on rifle

actions (which define the chamber) make many extreme dimensional ratios

impractical or unsafe. Likewise, changes in the case geometry can change the rate

at which a powder burns and/or the chamber pressure produced in unpredictable ways. Performance is not always a predictable extrapolation from known data taken from existing cartridges and can produce unexpected results in practice that differ from theoretical or extrapolated calculations. Combinations that are possible to construct may exhibit impractical and/or unexpected characteristics. For example, they may cause extraordinary barrel wear, may produce unexpected chamber pressures, or affect the metal case in a way that shortens its useful life (number of times it can be reloaded safely).

[0007] Another limitation is the rifle action (receiver and bolt) into which the

cartridge will be chambered and from which the projectile will be propelled (through

the barrel bore). A bolt-rifle's action has an elongated opening aft of the chamber

through which a cartridge is received. The length of this opening limits the cartridge

overall length (OAL) that can be inserted. This opening length essentially defines the

length of the action. The width of the action opening and bolt face diameter limits the

diameter of the accepted cartridge(s). Typically, a rifle bolt can be made to fit an

action length in a limited range of bolt face diameters to accommodate the base

diameter of a cartridge. Thus, actions are produced in only a limited number of action

groups or "classes."

[0008] In these standard groups, a "short action" accepts a cartridge with a

maximum OAL of 2.84 inches and, in standard width, a maximum diameter of 0.473

inch. This is sized to receive the 308 Winchester cartridge, for example. A "long

action" closely accepts a cartridge with a maximum OAL of 3.34 inches and, in

standard width, a maximum diameter of 0.473 inch. This is sized to receive the .30

'06 Springfield cartridge, for example. A "magnum action" accepts a cartridge with a

maximum OAL of 3.681 inches and a maximum diameter of 0.588 inch. This is sized

to optimally receive up to the .338 Lapua Magnum cartridge, for example. A "BMG action" or "50 BMG action" accepts a cartridge with a maximum OAL of 5.54 inches and a maximum diameter of 0.804 inch. This is sized to receive the .50 BMG and

.416 Barrett, for example.

[0009] The .50 caliber BMG (Browning Machine Gun) was developed from

John Browning's design in 1917. The original loading was an 800 grain bullet fired at

a velocity of 2,650 feet per second (fps) out of a 46" barrel. It was later loaded with a

900 grain bullet fired at 2,500 fps. In recent decades, the .50 BMG has gained

popularity among civilian shooters as a 1,000+ yard target rifle. Currently, the .50

BMG is commonly loaded with a 650 grain bullet fired at 3,000 fps. It is designed to

be effective past 2,000 meters or 2,500 yards.

[00010] There are several practical limitations to improving the performance of

cartridge loads for the .50 BMG. First, its case has a very large powder capacity

(more than 290 grains H 2 0 or almost 19cm 3 ). Less powder volume is needed with

modern propellants, meaning the case may only be partially filled and only slow

burning powders can be effectively used. Empty space inside the case allows the

powder to be positioned differently from one shot to the next, often resulting in

velocity variations. Empty air space in a partially filled case can affect how the

powder burns, a significant effect resulting from the empty space not being found at

the end of the case nearest the projectile. Instead, since a rifle is likely to be fired at

an angle near horizontal, the empty space could unevenly extend the length of the

case, unpredictably affecting how the powder is ignited by the primer and how the

burn spreads through the case.

[00011] A cartridge known as the .416 Barrett (10.6 x 83mm) addressed some

of these limitations. Using the .50 BMG as its parent case, it was shortened and

necked-down to accept a .416 caliber bullet. This reduced the case capacity to about

200 grains H20 (13cm 3 ) and allowed a 398 grain (gr) bullet to be propelled at an

average of 3,150 fps from a 32-inch barrel.

[00012] There are various original design cartridges that have used a .375

caliber projectile, including the .375 Belted Rimless Nitro-Express (by Holland

& Holland), the .375 Holland & Holland Magnum, and the .378 Weatherby Magnum.

Since then, various cartridges loading a .375 caliber bullet have been developed

from parent cartridges in the "magnum" family, such as the .375 Ruger and the .376

Steyr, and the .375 Lethal Magnum, using a belted case. Previously, a .375 caliber

cartridge has not successfully been produced from a parent cartridge in the 50 BMG

family.

Summary of the Invention

[00013] The present inventors set out to develop a center-fire cartridge load

and bullet combination that would produce a predictable shot out to at least 5,000

yards (4,572 meters). The present invention can utilize a .416 Barrett case as its

parent, whose base is the same as that of a .50 BMG cartridge (up to 0.804 inches in

diameter), reconfiguring the geometry of the case with a higher angle shoulder and a

neck to seat a .375 caliber (9.5mm) projectile having a mass in the range of 350

grains to over 400 grains, for use in a 50 BMG class action. The case configured

according to one embodiment of the present invention has a shoulder angle of at

least 400 and less than 450 and provides an average case capacity of about 220

grains H20 (about 14.4 cm 3 ) and cartridge overall length (OAL) of 4.825 inches.

[00014] The sharper 400 shoulder angle provides longer case life than

shallower angles due to reduced material flow during peak pressures. With

traditional 20°-30° shoulder angles, internal pressures cause the brass case to "flow"

forward, resulting in thin necks and shoulder junctions. Thin spots eventually result in cracked cases that are no longer usable for reloading. The .416 Barrett cartridge, for example, has a 250 shoulder angle, while the .50 BMG cartridge has a shoulder angle of slightly under 160(15 degrees, 44 minutes). The present cartridge has been found to be reloadable at least four times without annealing or trimming. The expectation is that it can be reloaded at least eight times, with necessary annealing and trimming procedures, without diminished performance.

[00015] With large cases, over-pressuring often results in the inability to extract

fired brass from the chamber. Unlike an "Ackley Improved" 40° shoulder, which

reduces body taper to maximize case capacity, the body taper in the present design

may be maintained at 0.850 to 1.00, for example approximately 0.9°.

[00016] The result is an advancement in the art that provides a long-range,

precision centerfire rifle cartridge capable of propelling a projectile having optimum

external ballistic characteristics to a higher muzzle velocity, as well as other

unexpected and unpredictable benefits. The cartridge does not perform according to

internal/external ballistic calculation predictions for the amount of propellant and

weight/BC of the projectile. Instead, its performance mimics that of a projectile

weighing 20% less. Measured muzzle velocities have averaged 3,150-3,200 fps with

a 361 grain bullet from a 34 inch barrel, which stays at supersonic speed beyond

3,000 yards. A 38 inch barrel is calculated to allow the same projectile to achieve at

least 3,300 fps.

[00017] Other aspects, features, benefits, and advantages of the present

invention will become apparent to a person of skill in the art from the detailed

description of various embodiments with reference to the accompanying drawing

figures, all of which comprise part of the disclosure.

Brief Description of the Drawings

[00018] Like reference numerals are used to indicate like parts throughout the

various drawing figures, wherein:

[00019] 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;

[00020] Fig. 2 is a side view thereof showing dimensional specifications

thereof;

[00021] Fig. 3 is a chamber reamer specification drawing (not to scale) for the

cartridge embodiment; and

[00022] Fig. 4 is a side view of a projectile according to an embodiment of the

invention.

Detailed Description

[00023] 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.

[00024] 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.

[00025] 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 400. 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 10, with the preferred taper

being at about 0.90. 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 400 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.

[00026] 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.

[00027] 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.

[00028] Examplel: A Flat Line T M .375 caliber bullet made by Warner Tool

Company of North Swanzey, New Hampshire, provides a 361 grain, solid copper

bullet having a 2.20 inch overall length (OAL). This projectile includes a 160 boat tail

and may be made in accordance with the invention described in U.S. Patent

Application Publication No. 2016/0327380, published November 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.

[00029] Example 2: A non-standard 400 grain, .375 caliber, solid copper bullet

made by Berger Bullets LLC of Fullerton, California. 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.

[00030] Example 3: A MTAC TM (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, Pennsylvania, having a G1BC=0.990 and OAL of 2.209

inches. This projectile requires a twist of 1:7.5 inches or faster.

[00031] 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,

Minnesota, 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.

[00032] 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.

[00033] 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.

[00034] The reference to any prior art in this specification is not, and should not

be taken as, an acknowledgement or any form of suggestion that such prior art forms

part of the common general knowledge.

[00035] It will be understood that the terms "comprise" and "include" and any of

their derivatives (e.g. comprises, comprising, includes, including) as used in this

specification, and the claims that follow, is to be taken to be inclusive of features to

which the term refers, and is not meant to exclude the presence of any additional

features unless otherwise stated or implied.

[00036] 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.

Claims (11)

WHAT IS CLAIMED IS:

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 1.00

relative to the central axis, a frusto-conical shoulder portion extending from the case

wall and having an angle of at least 40° and less than 450 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

having a weight of at least about 350 grains.

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 ofabout 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 H20.

6. The cartridge of claim 5, wherein the case has a capacity in the range

of about 210-230 grains H20.

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.

10. The cartridge of claim 1, wherein the projectile has a weight of about 361

grains, and wherein the projectile has a muzzle velocity of at least 3,300 feet per

second when fired from a 38 inch barrel.

11. The cartridge of claim 10, wherein velocity of the projectile stays supersonic

past 3,000 yards when fired through the 38 inch barrel having a twist rate of 1:8.65

inches.