WO2001033155A2

WO2001033155A2 - Subsonic cartridge for gas-operated automatic and semiautomatic weapons

Info

Publication number: WO2001033155A2
Application number: PCT/US2000/028145
Authority: WO
Inventors: John D. Leasure
Original assignee: Leasure John D
Priority date: 1999-10-12
Filing date: 2000-10-12
Publication date: 2001-05-10
Also published as: AU3789101A; WO2001033155A3

Abstract

A subsonic cartridge (10) that enables a conventional automatic or semiautomatic weapon (36) to fire a projectile (30) at a subsonic velocity and cycle the weapon (36) to eject the spent cartridge case (12), without the sonic report characteristic of supersonic projectile (30) velocities. The cartridge (10) includes a case (12) having a tubular shape with an open end (16), an oppositely disposed head (18), and a bore (14) therebetween. The head (18) of the case (12) includes a primer cavity (22), a web (24) separating the primer cavity (22) from the bore (14), and a flash hole (26) through the web (24). A primer (28) is stored within the primer cavity (22), and a projectile (30) is disposed within the bore (14) so as to close the open end (16) of the cartridge case (12). A charge cavity (34) is delimited within the bore (14) between the web (24) and the projectile (30). The charge cavity (34) is sized and shaped to contain a limited amount of propellant charge (32) that propels the projectile (30) from the cartridge case (12) at a subsonic speed.

Description

SUBSONIC CARTRIDGE FOR GAS-OPERATED AUTOMATIC AND SEMIAUTOMATIC WEAPONS

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part patent application of co-pending United States patent application Serial No. 08/788,216, filed January 27, 1997.

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION

The present invention generally relates to firearm cartridges, including those for use in automatic and semiautomatic weapons. More particularly, this invention relates to a cartridge for propelling a projectile at subsonic velocities and which is capable of cycling the reciprocating bolt of a gas-operated automatic and semiautomatic weapon.

2. DESCRIPTION OF THE PRIOR ART

Many automatic and semiautomatic weapons are gas-operated, in that they use cartridge ammunition with a propellant charge that is not only adequate to expel the projectile (bullet) from the cartridge case and weapon, but must also develop sufficient chamber pressure to cycle the reciprocating bolt of the weapon, during which the spent case is ejected and the next cartridge is loaded. There are various types of cartridges for projectiles used in gas-operated automatic and semiautomatic weapons. For example, different cartridge cases are available for .223 caliber (5.56 mm) bullets fired from the United States Model Colt M-4 and M-16/AR-15 weapons. These weapons fire .223 caliber projectiles at velocities of approximately 3000 feet/second (about 900 m/s), i.e., far exceeding the speed of sound (about 330 m/s, or about 1100 feet/second). It is believed that a cartridge is not available for use with conventional gas-operated automatic or semiautomatic weapons, which can cycle the weapon to eject a spent cartridge case yet also propel the projectile at a subsonic velocity to reduce the level of sound at firing, i.e., to avoid the sonic report produced as a result of the projectile exceeding the speed of sound. More particularly, a cartridge is not available that can fire a projectile at a subsonic speed and simultaneously develop sufficient chamber pressure to cycle the reciprocating bolt of a gas-operated weapon. As an example, a subsonic cartridge is not available that can develop a chamber pressure of at least 45,000 psi (about 3100 bar), which is generally required to cycle the Colt M-4 weapon when firing a .223 caliber cartridge.

The use of a sound suppressor, silencer or sound moderator to reduce the sound produced by a weapon is well known, an example being the integrated sound suppression available for gas-operated automatic and semiautomatic weapons such as the M-4 and M-16/AR-15 weapons. While being effective to considerably reduce the sound level produced when fired, conventional sound suppression devices cannot suppress the loud report of a supersonic projectile. Because of the present requirement to use supersonic cartridges to produce chamber pressures sufficient to cycle their reciprocating bolts, gas-operated automatic and semiautomatic weapons produce a sonic report even though equipped with sound suppression. U.S. Patent No. 5,033,356 to Richardson discloses a firearm noise suppressor that reduces the velocity of a projectile fired using a cartridge. Richardson explains that in most situations, the noise suppressor reduces the projectile velocity to subsonic speeds. However,

Richardson uses conventional ammunition, and then modifies the firearm barrel to include an external chamber into which gases are vented as the projectile travels through the bore past a port that vents the bore to the chamber. One example presented by Richardson involves firing a conventional supersonic round at a subsonic velocity. However, in the example an AR- 15 9 mm weapon is used, which is not gas- operated.

In view of the above, it can be appreciated that there is a need for a cartridge that is capable of cycling a reciprocating bolt of a gas-operated automatic or semiautomatic weapon, as well as capable of propelling a projectile from such a weapon at subsonic velocity, so that the weapon produces minimal sound when fired.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a subsonic cartridge that enables a conventional gas-operated automatic or semiautomatic weapon to fire a projectile at a subsonic velocity and cycle the weapon to eject a spent cartridge case, without the sonic report characteristic of supersonic projectile velocities. The present invention is suitable for use with gas-operated weapons having attached or integral sound suppressors, silencers or sound moderators, to provide the capability of even further sound reduction. According to the present invention, the subsonic cartridge includes a cartridge case having a tubular shape with an open end, an oppositely disposed head, and a bore therebetween. The head of the case includes a primer cavity, a web separating the primer cavity from the bore, and a flash hole through the web. A primer is stored within the primer cavity, and a projectile is secured within the open end of the cartridge case. A charge cavity is delimited within the bore between the web and the projectile. According to this invention, the charge cavity has a noncylindrical shape, having a reduced capacity than if the diameter of the charge cavity was constant and the same as that of the projectile. In a preferred embodiment, the charge cavity is tapered so that the cross-sectional area of the charge cavity adjacent the projectile is greater, preferably at least 50% greater, than the cross- sectional area of the charge cavity adjacent the web. Finally, a propellant charge is contained within the charge cavity in an amount sufficient to propel the projectile from the cartridge case at a subsonic speed.

According to the above, the present invention provides a cartridge with a charge cavity that is sized and shaped to contain an amount of propellant charge that will propel a sufficiently heavy projectile at a subsonic velocity. As used herein, a "sufficiently heavy" projectile is heavier than projectiles conventionally used with a given cartridge, and preferably formed of a material that is more dense than lead. The shape of the charge cavity limits the amount of propellant charge that can be contained in the cartridge case. In the preferred embodiment, the tapered shape of the charge cavity positions relatively less propellant charge immediately adjacent the primer, which is believed to reduce temperature velocity variations during combustion of the propellant charge. According to the invention, the amount of propellant charge is also sufficient to cycle a gas-operated reciprocating bolt of an automatic or semiautomatic weapon if a sufficiently heavy projectile is used. Accordingly, the cartridge of the present invention enables a subsonic round to be fired from a gas-operated automatic or semiautomatic weapon, without requiring any modifications to the weapon. Such a weapon can be equipped with a sound suppression device in order to further reduce the level of sound produced when a subsonic round of this invention is fired.

Other objects and advantages of this invention will be better appreciated from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional view of a cartridge configured in accordance with a preferred embodiment of the present invention;

Figure 2 is an exploded view of the cartridge of Figure 1; and Figure 3 is a sectional view of a Model Colt M- 16/AR- 15 automatic weapon in which cartridges in accordance with Figures 1 and 2 are loaded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of a cartridge 10 of this invention is shown in Figures 1 through 3. The cartridge 10 depicted is a .223 caliber (5.56 mm), though the teachings of this invention can be applied to calibers of .22 to .50 if appropriate adjustments are made for propellant charge and projectile weight, as explained below. As is generally conventional, the cartridge 10 is composed of a case 12 that may be formed of brass, such as casings manufactured by Olin Winchester. The case 12 has a generally tubular shape with an internal bore 14, an open end 16 and an oppositely- disposed head 18. The case 12 is shown as having a flange or crimp 20 at an angle of about 23 degrees from the longitudinal axis of the case 12, though it is foreseeable that crimps at different angles could be used. The case 12 has an overall length of about 1.76 inches (about 44.7 mm), and outer diameters of about 0.378 inch (about 9.60 mm) at the head 18, about 0.354 inch (about 8.99 mm) adjacent the crimp 20, and about 0.253 inch (about 6.43 mm) at the open end 16. The length of the case 12 from the head 18 to the crimp 20 is about 1.438 inches (about 36.53 mm). The internal diameter of the open end 16 is about 0.224 inch (about 5.69 mm). Those skilled in the art will appreciate that the above dimensions are by example for a .223 caliber cartridge, and that the dimensions of the case 12 can differ, particularly for different calibers.

As is generally conventional, the head 18 includes a primer cavity 22, a web 24 that separates the primer cavity 22 from the bore 14, and a flash hole 26 through the web 24 so that the primer cavity 22 communicates with the bore 14. The flash hole 26 is generally aligned on the longitudinal axis of the bore 14. The primer cavity 22 contains a boxed primer 28, such as any one of those commercially available from Olin Winchester, C.C.I., Remington Arms Co. and others. The boxed primer 28 is preferably classified as a C.C.I. 41 military sensitivity primer.

A projectile 30 is secured within that portion of the bore 14 at the open end 16. The projectile 30 has a diameter of about 0.223 inch (about 5.66 mm), corresponding to the caliber of the cartridge 10. The projectile 30 can be formed of various materials. However it has been unexpectedly found that, in order to cycle a gas-operated weapon in accordance with this invention, the projectile must be heavier than conventionally used for the particular caliber of the cartridge 10. For example, a conventional .223 cartridge employs a projectile weighing about 40 to 80 grains (about 2.6 to 5.2 g), typically about 55 grains (about 3.6 grams) for a conventional .223 caliber Remington round and about 62 grains (about 4.0 g) for military cartridges. In contrast, projectiles 30 for the cartridge 10 of this invention preferably weigh at least 100 grains (about 6.5 grams), more preferably about 130 grains to about 185 grains (about 8.4 grams to about 12.0 grams) for the .223 caliber cartridge 10 shown in Figures 1 and 2. For other calibers, it is believed that suitable projectiles are preferably at least 25% heavier, more preferably at least 50% heavier, than the maximum projectile weight for a conventional cartridge commercially available for the caliber. Otherwise, it is believed that the cartridge 10 would not properly cycle a gas-operated weapon.

In view of the above, the projectile must either be physically larger or formed of a relatively denser material than conventionally used, i.e., specific gravities greater than 11.7 for lead. Suitable materials for the projectile 30 include high-density lead alloy cores having a coated copper jacket exterior, such as those manufactured by Alfred Bullet Co., Serria Bullets, etc. More preferred materials for the projectile 30 include high-impact high-density frangible tungsten composite projectiles, such as those manufactured by Genesis Environmental Technology. In a preferred embodiment, the overall length of the cartridge 10 (case 12 with projectile 30) is about 2.223 inches (about 5.646 cm). Those skilled in the art will appreciate that if the projectile is formed of lead, the length of the projectile 30 must be increased to achieve the weight required by this invention, and that the weapon from which the projectile 30 is fired may require a particular barrel twist and/or barrel length to stabilize the projectile. For example, an M-4 may require a barrel length of about 14.5 inches (about 36.8 cm) and a l-in-7" rifle twist to stabilize a projectile formed from lead.

Contained within the bore 14 between the web 24 and projectile 30 is a propellant charge 32, such as gun powder composition commercially available under the name Hodgdon 870 from Hodgdon Powder Company, Inc. Other suitable gun powders are commercially available from Dupont, Accurate Powder, Hercules and Vihtavouri Oy. According to this invention, the amount of propellant charge 32 contained within the bore 14 is less than that conventionally used in order to propel the unconventionally heavy projectile 30 of this invention at a subsonic velocity. More preferably, the case 12 contains a sufficient amount of the propellant charge 32 to expel the projectile 30 from the barrel of a weapon at a subsonic velocity of about 1050 feet/second (about 320 m/s). A preferred amount of propellant charge 32 for the .223 caliber cartridge 10 of Figures 1 and 2 is 14.0 grains (about 0.907 g) or less. The amount of propellant charge 32 required to achieve subsonic performance will inherently vary with projectile weight. For example, the amount of charge 32 is increased/decreased with an increasing/decreasing mass, respectively, for the projectile 30. In an M-4 .223 caliber weapon having a gas-operated reciprocating bolt and a barrel length of about ten to twenty inches (about twenty-five to fifty centimeters), the propellant charge 32 must be sufficient to produce a chamber pressure of at least 45,000 psi (about 3100 bar), preferably about 45,000 psi to 51,000 psi (about 3500 bar). Those skilled in the art will appreciate that the required chamber pressure will depend in part on the caliber and barrel length of the weapon from which the projectile 30 is fired.

A key aspect of the present invention is that the bore 14 of the case 12 is shaped to properly contain and position the propellant charge 32 within the case 12 to facilitate uniform powder burn, resulting in positive powder ignition, uniform pressures and uniform velocities. That portion of the bore 14 containing the propellant charge 32 will be referred to as the charge cavity 34. As shown, the charge cavity 34 is delimited within the bore 14 by the web 24 and projectile 30, and has a uniformly and continuously tapered shape. The volume of the charge cavity 34 is critical, in that it is sized to accommodate not more than enough propellant charge 32 to maintain subsonic velocity and function, e.g., 14 grains of propellant charge 32 for the .223 of Figures 1 and 2. Based on the uniform taper shown, the charge cavity 34 has a cross-sectional area adjacent the projectile 30 that is at least 50% greater than its cross-sectional area adjacent the web 24. When completely filled with the propellant charge 32, the uniformly tapered shape of the charge cavity 34 improves reliability, powder burn, and temperature/velocity variations. However, the charge cavity 34 could have a noncylindrical shape other than that shown in the Figures and still achieve the object of this invention.

The cartridge 10 of this invention is intended for loading in conventional gas-operated automatic or semiautomatic weapons, such as the Colt M- 16/AR-15 weapon 36 depicted in Figure 3. The .223 caliber cartridge 10 of Figures 1 and 2 can also be adapted to operate in other M-16 rifles having barrel lengths of about ten to twenty inches, as noted above. The weapon 36 is shown in Figure 3 without an attached or integral sound suppressor, silencer or sound moderator, though it is within the scope of this invention that the weapon 36 could be so equipped as well known in the art. An example of a suitable sound suppressor is a silencer disclosed in U.S. Patent No. 5,164,535 to LeaSure.

As depicted in Figure 3, several cartridges 10 are loaded into a magazine 40 assembled to the weapon 36, whose firing sequence is well known to those skilled in the art. When the trigger of the weapon 36 is pulled, the propellant charge 32 is ignited by the primer 28, producing gases 42 that rapidly expand to dislodge the projectile 30 from the case 12 and propel the projectile 30 down the barrel 44 of the weapon 36. In the gas-operated weapon 36, the expanding gases 42 also fill a cavity 46 within a bolt carrier 48 of the weapon 36, by which the bolt carrier 48 is cycled to eject the spent case 12 and load the next cartridge 10 from the magazine 40. The expanding gases 42 enter the cavity 46 by traveling from the spent case 12 down the barrel 44 into a gas port 50 of a gas tube assembly located under the front sight assembly 52 of the weapon 36, as depicted in Figure 3. As noted above, the expanding gases 42 preferably create a chamber pressure of about 45,000 psi to about 51,000 psi, depending on the length of the barrel 44. As the expanding gases 42 fill the cavity 46, the bolt carrier 48 is cycled rearward, causing an extraction and ejection cycle such that the case 12 from the discharged cartridge 10 is ejected from the weapon 36. Extraction of the next cartridge 10 from the magazine 40 occurs as the reciprocating bolt 54 and bolt carrier 48 are in a forward cycle, during which the bolt 54 strips the next cartridge 10 from the magazine 40 into the barrel chamber 56 of the weapon 36, which is then ready for firing.

In an initial investigation, cartridges similar in outward appearance to that shown in Figure 1 were evaluated. The cartridges had heavy projectiles (100 grains, about 6.5 g) and a reduced propellant charge, but a conventional case. The cartridges were fired from an M-16 weapon having a barrel length of about 14.5 inches (about 36.8 cm), with ballistic data gathered with the assistance of Barnes Bullets, Inc. The weapon was fired with and without an attached suppressor. When fired, the cartridges cycled the weapon without producing a loud sonic report, i.e., did not exceed the speed of sound. The chamber pressure measured during firing of the cartridges was about 51,000 psi (about 3500 bar), and muzzle velocities of the projectiles were about 1050 fit/sec (about 320 m/s). Projectile velocities were about 984 fit/sec (about 300 m/s) after traveling about 150 meters, suggesting an effective range of over 200 meters. When the cartridges were fired from the weapon with an attached sound suppressor, almost no sound was produced. From these tests, it was concluded that a cartridge with a heavier projectile and reduced propellant charge could achieve subsonic projectile velocities when fired from a gas-operated automatic or semiautomatic weapon having a length of about ten to twenty inches (about 25 to 50 cm).

In a subsequent investigation leading to this invention, .223 caliber cartridges configured in accordance with Figures 1 and 2 underwent ballistic testing using a gas-operated Colt M-4 carbine having a barrel length of about 14.5 inches (about 36.8 cm) and with and without a silencer. The test showed that the cartridge of this invention was able to propel 145 grain, .223 projectiles at subsonic velocities and properly cycle the weapon. Chamber pressures of about 48,000 psi (about 330 bar) were measured for exit velocities of about 1040 ft/s (about 317 m/s), with a velocity of about 1000 ft/s (about 305 m/s) being measured after the projectiles had traveled about 300 feet (about 90 m). From these tests, it was concluded that .223 caliber projectiles fired from the tested weapon would have an effective range of at least 250 yards (about 230 m). From the above tests, it was further concluded that the invention is particularly advantageous for .308 caliber (7.62 mm) cartridges. For this caliber, a suitable projectile and propellant charge combination is believed to be about 180 to about 300 grains (about 11.7 to about 19.4 g) for the projectile 30 and about 14 to 18 grains (about .91 to about 1.2 g) for the propellant charge 32. As previously noted, different calibers can benefit from this invention, as long as the projectile and propellant charge are appropriately increased and decreased together to maintain the desired subsonic performance, Therefore, while the invention has been described in terms of a preferred embodiment, it is apparent that other forms could be adopted by one skilled in the art. In addition to different calibers, cartridges within the scope of this invention can have configurations that differ from that shown in the Figures, and appropriate materials could be substituted for those noted. Accordingly, the scope of the invention is to be limited only by the following claims.

Claims

What is claimed is:

1. A cartridge (10) comprising: a cartridge case (12) having a tubular shape with an open end (16), an oppositely disposed head (18), and a bore (14) therebetween, the head (18) having a primer cavity (22), a web (24) separating the primer cavity (22) from the bore (14), and a flash hole (26) through the web (24); a primer (28) stored within the primer cavity (22); a projectile (30) disposed within the bore (14) so as to close the open end (16) of the cartridge case (12); a charge cavity (34) delimited within the bore (14) between the web (24) and the projectile (30), the charge cavity (34) having a noncylindrical shape; and a propellant charge (32) contained within the charge cavity (34) in an amount sufficient to propel the projectile (30) from the cartridge case (12) at a subsonic speed.

2. A cartridge (10) according to claim 1, wherein the charge cavity (34) has a tapered shape so as to have a cross-sectional area adjacent the projectile (30) that is at least 50% greater than a cross-sectional area of the charge cavity (34) adjacent the web (24).

3. A cartridge (10) according to claim 1, wherein the charge cavity (34) has a uniformly and continuously tapered shape.

4. A cartridge (10) according to claim 1, wherein the cartridge (10) is a .223 caliber, the projectile (30) weighs at least 100 grains, and the charge cavity (34) is sized to accommodate not more than 14 grains of the propellant charge (32).

5. A cartridge (10) according to claim 4, wherein the projectile (30) has a weight of about 135 grains to 180 grains.

6. A cartridge (10) according to claim 4, wherein the propellant charge (32) completely fills the charge cavity (34).

7. A cartridge (10) according to claim 1, wherein the cartridge (10) is a .308 caliber, the projectile (30) weighs about 180 to about 300 grains, and the charge cavity (34) is sized to accommodate about 14 to about 18 grains of the propellant charge (32).

8. A cartridge (10) according to claim 7, wherein the propellant charge (32) completely fills the charge cavity (34).

9. A cartridge (10) according to claim 1, wherein the projectile (30) has a specific gravity of greater than 11.7.

10. A cartridge (10) according to claim 1, wherein the projectile (30) has a caliber of from .22 to .50.

11. A cartridge (10) according to claim 1, wherein the cartridge (10) is loaded in a weapon (36) chosen from the group consisting of gas-operated automatic and semiautomatic weapons.

12. A cartridge (10) according to claim 10, wherein the weapon (36) has a barrel length of about 10 to about 20 inches.

13. A cartridge (10) according to claim 10, wherein the cartridge (10) is a .223 caliber, the projectile (30) weights at least 100 grains, and the amount of the propellant charge (32) present in the charge cavity (34) is sufficient to produce a pressure of about 45,000 psi to 51,000 psi when ignited to propel the projectile (30) from the cartridge case (12).

14. A process of firing a cartridge (10) from a gas-operated automatic or semiautomatic weapon (36), the process comprising the steps of: providing a cartridge (10) comprising: a cartridge case (12) having a tubular shape with an open end (16), an oppositely disposed head (18), and a bore (14) therebetween, the head (18) having a primer cavity (22), a web (24) separating the primer cavity (22) from the bore (14), and a flash hole (26) through the web (24); a primer (28) stored within the primer cavity (22); a projectile (30) disposed within the bore (14) so as to close the open end (16) of the cartridge case (12); a charge cavity (34) delimited within the bore (14) between the web (24) and the projectile (30); and a propellant charge (32) contained within the charge cavity (34) in an amount sufficient to propel the projectile (30) from the cartridge case (12) at a subsonic speed; loading the cartridge (10) in a gas-operated weapon (36) chosen from the group consisting of automatic and semiautomatic weapons having a reciprocating bolt (54); and then firing the weapon (36) by igniting the propellant charge (32), the propellant charge (32) producing a chamber pressure sufficient to propel the projectile (30) from the cartridge case (12) at a subsonic speed and to recycle the reciprocating bolt (54) of the weapon (36).

15. A process according to claim 14, wherein the cartridge (10) is a .223 caliber, the projectile (30) weighs at least 100 grains, and the charge cavity (34) is sized to accommodate not more than 14 grains of the propellant charge (32).

16. A process according to claim 15, wherein the projectile (30) has a weight of about 135 grains to 180 grains.

17. A process according to claim 15, wherein the propellant charge (32) completely fills the charge cavity (34).

18. A process according to claim 14, wherein the cartridge (10) is a .308 caliber, the projectile (30) weighs about 180 to about 300 grains, and the charge cavity (34) is sized to accommodate about 14 to about 18 grains of the propellant charge (32).

19. A process according to claim 18, wherein the propellant charge (32) completely fills the charge cavity (34).

20. A process according to claim 14, wherein the projectile (30) has a specific gravity of greater than 11.7.

21. A process according to claim 14, wherein the projectile (30) has a caliber of from .22 to .50.

22. A process according to claim 14, wherein the weapon (36) has a barrel length of about 10 to about 20 inches.

23. A process according to claim 14, wherein the cartridge (10) is a .223 caliber, the projectile (30) weights at least 100 grains, and the amount of the propellant charge (32) present in the charge cavity (34) is sufficient to produce a pressure of about 45,000 psi to 51,000 psi when ignited to propel the projectile (30) from the cartridge case (12).