WO2003060418A2

WO2003060418A2 - Subsonic and reduced velocity ammunition cartridges

Info

Publication number: WO2003060418A2
Application number: PCT/US2003/000913
Authority: WO
Inventors: Brad Mackerell; Ryan Payne
Original assignee: Tti Armory, L.L.C.
Priority date: 2002-01-11
Filing date: 2003-01-13
Publication date: 2003-07-24
Also published as: US20030131751A1; WO2003060418A3; AU2003202963A8; AU2003202963A1

Abstract

Subsonic and reduced velocity rifle ammunition cartridges are disclosed. The ammunition cartridges can be fired through a standard rifle with a common twist rate at subsonic and reduced velocities. The subsonic ammunition uses propellant that is not typically used with the selected rifle cartridge. Cycling subsonic ammunition cycles the firing and loading mechanisms of fully automatic and semiautomatic weapons. Cycling subsonic ammunition cartridges contain slow burning propellant, such as cannon powder, and a heavy projectile with a long bearing surface. Non-cycling subsonic ammunition uses moderately fast burning pistol propellant. The projectiles are carefully selected to be stable at subsonic or reduced velocities and at the standard rifle twist rate for given cartridge caliber.

Description

SUBSONIC AND REDUCED VELOCITY AMMUNITION CARTRIDGES

Field of the Invention

The invention is directed to subsonic and reduced velocity ammunition cartridges used with standard rifles having standard rifle twist rates.

Background of the Invention

Modern firearms use a cartridge which includes a casing that houses a quantity of propellant, a primer, and a projectile. The design and configuration of ammunition cartridges have changed little over the last 75 years. Cartridges are typically designed to propel projectiles at supersonic velocities, i.e. at a muzzle velocity greater than approximately 1086 ft/sec. at sea level under standard conditions of temperature and pressure. The faster a projectile travels, the flatter is its trajectory to its target. Also faster projectile speeds tend to reduce the effects of lateral wind forces upon the projectile path to its target. Therefore, it has been the practice of firearm and ammunition manufacturers to maximize the quantity of propellant used to propel the projectile, consistent with the permissible pressure for a given weapon, as a means of increasing projectile velocity and accuracy.

Projectiles traveling at supersonic speeds generate a noticeable and traceable supersonic crack during their free flight to the target. This sound, and/or the sound generated by the projectile breaking the sound barrier, can be used to locate the source of the weapon from which the projectile was fired. In military, law enforcement, and covert operations, there is often a need to conceal the location of shooters and sniper positions. The use of suppressors (silencers) are important to mask sound and in some instances location of the shooter. However, most modern cartridges still have a noticeable and traceable supersonic crack that cannot be masked by the use of a suppressor. One partial solution to this problem is to restrict the speed of travel of the projectile to a subsonic speed.

For many years gun and ammunition manufacturers have attempted to produce subsonic ammunition that will perform reliably and accurately in conventional firearms. It is highly undesirable to require specially modified firearms suitable for only subsonic ammunition. Subsonic ammunition cartridges should be interchangeable with supersonic rounds and fit properly in the same firearm chamber. The typical approach by manufacturers is to reduce the quantity of propellant charge in the cartridge. However, this approach has not worked for several reasons. When the quantity of propellant is reduced relative to the total volume within the cartridge case, inconsistent propellant ignition can result. This inconsistency is due to the charge being inconsistently positioned inside the case relative to the primer. For example, when shooting downward, the propellant may move forward in the cartridge case, away from the primer, affecting propellant ignition, pressure, and resulting projectile velocity. In contrast, when shooting upward, the propellant may move rearward in the cartridge case, towards the primer, which also affects propellant ignition, pressure, and projectile velocity. Thus, propellant ignition and projectile velocity is inconsistent and unreliable when one simply reduces the quantity of propellant in a given cartridge volume.

Several solutions to this problem have been proposed in the art, including the addition of inert and consumable filler materials to the propellant, expandable inner sleeves that occupy the empty cartridge space (U.S. Pat. No. 4,157,684), an inner tube of propellant inserted within the cartridge (U.S. Pat. No. 6,283,035), a molded foam filler to reduce the internal casing volume (U.S. Pat. No. 5,770,815), and multiple stepped down stages in the discharge end of the cartridge casing to reduce the internal casing volume (U.S. Pat. No. 5,822,904).

Another problem with reducing the quantity of propellant is the inability of the ammunition to cycle the firing mechanisms of fully automatic and semi-automatic weapons. For automatic weapons to properly cycle, the propellant charge must produce sufficient gas pressure to accelerate the projectile and to cycle the firing mechanism. Typical chamber pressures will be in the range from 35,000 psi to 55,000 psi. With a reduced quantity of propellant, subsonic ammunition generally fails to produce sufficient pressure to accelerate the projectile and to properly cycle the firing mechanism of automatic weapons.

Yet another significant problem with subsonic ammunition is inaccurate performance. The projectile should exhibit stable flight under subsonic conditions. While standard rifles and projectiles are designed for stable supersonic flight, it is often not possible to achieve stable subsonic flight utilizing a standard projectile and typical rifling in rifle barrels. Standard rifle projectiles fired at subsonic velocities tend to tumble in flight, which results in extremely poor performance.

It will be appreciated that there is a need in the art for subsonic ammunition that is accurate, consistent, and reliable, that can use conventional cartridge loading equipment, that can use standard cartridges designed for standard firearm chambers and standard rifle barrels. It would also be an advancement in the art to provide subsonic ammunition that is able to cycle the firing mechanisms of automatic weapons. Summary of the Invention

The invention is drawn to ammunition cartridges or rounds that can be fired through a standard rifle with a common twist rate at subsonic and reduced velocities. The invention uses standard rifle cartridges, which include centerfire rifle cartridges generally recognized as being fired from standard rifles. "Cycling" subsonic ammunition is specifically designed to cycle the firing and loading mechanisms of fully automatic and semiautomatic weapons. "Standard" subsonic ammunition is not designed to cycle automatic and semiautomatic weapons. Both standard and cycling subsonic ammunition may be used with "standard rifles" or common, commercially available rifles. Unlike the prior art, the present invention does not modify the standard rifle cartridge shape and does not include cartridge inserts, fillers, elongated projectiles, or other structures to reduce the cartridge case volume.

Non-conventional powders (propellants) and projectiles stable at subsonic or reduced velocity are used with the subsonic ammunition within the scope of the present invention. "Non-conventional powders" are powders not typically used in the selected rifle cartridge. Moderately fast-burning pistol propellant may be used in the "standard" subsonic ammunition. A slow burning cannon propellant may be used in the "cycling" subsonic ammunition. Such propellants are not known for use with small arms ammunition. Computer software may be used to simulate propellant ballistic properties in a given cartridge. This can help in selecting and pre-screening a suitable propellant and determining the quantity of propellant. The propellant powder is preferably spherical powder to facilitate accurate dispensing in automatic loading equipment.

The projectiles are selected to be stable at subsonic or reduced velocities and at the standard rifle twist rate for the given rifle cartridge caliber. One or more commercially available bullet stability calculator may be used to assist in preliminary projectile selection and screening. The final selection and optimization can only be made after laboratory and field testing.

Without being bound by theory, projectiles with ratios (D:L) of approximately one are generally stable at subsonic and reduced velocity. In addition, projectiles in which the center of mass is approximately equal to the midpoint of the projectile tend to be more stable at subsonic and reduced velocity. Other projectiles may be made more stable by moving the center of pressure behind the center of mass. This may be accomplished by introducing drag to the rear of the projectile. In addition, the rifle twist rate affects projectile selection. For example, a broader variety of projectiles are stable at higher twist rates. Fewer projectiles are stable when fired from low twist rate rifles. Cycling subsonic projectiles are generally heavier projectiles with a longer bearing surface for increased drag within the bore and gas seal in the barrel. In this way, the projectile is expelled more slowly. Instead of using moderately fast burning pistol propellants, extremely slow bum rate propellants, such as cannon powders, are used. The slow burning propellant combined with a heavy, slower projectile result in a longer resident time within the rifle bore. This keeps pressure high enough to expel the projectile at subsonic velocities and still cycle actions.

The foregoing subsonic ammunition within the scope of the present invention is highly accurate at a range up to about 200-800 yards, depending on the caliber.

The subsonic ammunition cartridges within the scope of the present invention may include cartridge casings that have been colored to identify them as subsonic ammunition. The cartridge casings may receive a color coating by electroplating or other durable coating technique. Black is a particularly preferred color, but other colors, such as olive green, brown, silver, gray or white may be used.

Detailed Description of the Invention

The invention is drawn to ammunition cartridges or rounds that can be fired through a standard rifle with a common twist rate at subsonic and reduced velocities. Two types of subsonic and reduced velocity ammunition are disclosed herein and identified as "standard" subsonic ammunition and as "cycling" subsonic ammunition. Both standard and cycling subsonic ammunition may be used with standard rifles, but cycling subsonic ammunition is specifically designed to cycle the firing and loading mechanisms of fully automatic and semiautomatic weapons.

As used herein, the term "standard rifle" refers to common, commercially available rifles. As used herein, the term "standard rifle cartridge casing" refers to centerfire rifle cartridge casings generally recognized as being fired from standard rifles and comprising unmodified brass. As used herein, the term "standard supersonic ammunition" refers to common, commercially available rifle ammunition using standard rifle cartridge casings designed to fire projectiles as supersonic velocity. Examples of typical standard rifle cartridge casings are identified in published cartridge reloading handbooks, such as Hornady Handbook of Cartridge Reloading. A list of some standard rifle cartridges is set forth in Table 1. It will be appreciated that Table 1 is not intended to be an exhaustive list of all possible rifle cartridges that may be used with the present invention and that the present invention is not limited to the rifle cartridges set forth in Table 1. Table 1 Some Standard Rifle Cartridges 7 Mach TV 7 X 57mm Mauser7 Remington 284 Winchester 2 Hornet 280 Remington 2 K-Hornet 7mm Express Remington18 Bee 7 X 65mm R 22 Remington 7 X 61mm Sharpe & Hart23 Remington 7mm Remington Magnum.56 X 45mm NATO 7mm Weatherby Magnum22 Remington Magnum 7mm Dakota 2 PPC 7mm STW .6 X 50mm Magnum 30 Ml Carbone 19 Donaldson Wasp 30-30 Winchester19 Zipper 7.5 X 54mm MAS25 Winchester 300 Savage 24 Weatherby Magnum 307 Winchester 2-250 Remington 7.62 X 5 lmm NATO20 Swift 7.62mm Russian .6 X 57mm RWS 7.62X 54mm R .6 X 52mm R (22 Savage High Power) 7.62 X 53mm R X 47mm 30-40 Krag mm PPC 30-06 mm BR Ml Garand 43 Winchester 300 H&H Magnummm Remington 308 Norma Magnummm-284 300 Winchester Magnum40 Weatherby Magnum 300 Weatherby Magnum5-20 WCF 300 Dakota 56 Winchester Magnum 300 Remington Ultra Magnum5-35 Winchester (25 Remington) 30-378 Weatherby Magnum50-3000 Savage 32-20 Winchester (32-20 WCF)57 Roberts 7.62 X 39mm, M4357 Roberts Improved 7.65mm Belgian Mauser5-06 Remington 303 British 57 Weatherby Magnum 7.7mm Japanese .5mm Japanese 32 Winchester Special.5mm Carcano 8mm Mauser (8 X 57mm S).5 X 54mm Mannlicher-Schoenauer 8mm-06 .5 X 55mm Swedish Mauser 8 X 68mm S 60 Remington 8mm Remington Magnum.5 X 57mm 33 Winchester .5mm-284 338-06 .5mm-06 338 Winchester Magnum.5mm Remington Magnum 330 Dakota 64 Winchester Magnum 340 Weatherby Magnum70 Weatherby Magnum 338 Lapua Magnum-30 Waters 338-378 Weatherby Magnummm-08 Remington 348 Winchester 357 Magnum (Rifle) 416 Remington 35 Remington 416 Dakota

358 Winchester 416 Weatherby Magnum

350 Remington Magnum 44-40 (Rifle)

35 Whelen 44 Remington Magnum (Rifle)

358 Norma Magnum 444 Marlin

38-55 Winchester/Ballard 45 Long Colt (Rifle)

375 Winchester 45-70 (Trap Door)

376 Steyr 45-70 Marlin (1895) 375 H&H Magnum 45-70 Ruger

375 Dakota 458 Winchester Magnum

378 Weatherby Magnum 460 Weatherby Magnum

416 Rigby 50 BMG

The subsonic ammunition within the scope of the present invention use modern non- conventional powders and carefully selected projectiles to assure stabilized flight and avoid damage to suppressor baffles. The term "non-conventional powder" refers to powder, or propellant, that is not typically used in the selected rifle cartridge. For example, typical moderately fast burning pistol propellant may be used in the "standard" subsonic ammunition within the scope of the present invention. The "cycling" subsonic ammunition within the scope of the present invention uses neither pistol nor rifle propellant. Instead, a cannon propellant is used that has a burn rate slower than conventional pistol and rifle propellants.

The projectiles used with the subsonic ammunition within the scope of the present invention are carefully selected to be stable at subsonic or reduced velocities and at the standard rifle twist rate for given cartridge caliber. For example, a typical rifle that fires a .223 caliber cartridge has a rifle twist rate of one turn in 9 inches, which is a relatively moderate twist rate. In contrast, a typical rifle that fires a .308 caliber cartridge has a rifle twist rate of one turn in 12 inches, which is a relatively slow twist rate.

The subsonic ammunition according to the present invention may be used with a sound suppressor to lower firing decibel levels and virtually eliminate a sound signature. Unlike known subsonic ammunition cartridges, the subsonic ammunition within the scope of the present invention avoids harmful fillers, special cartridge inserts, cartridge shape modifications, and elongated projectiles that reduce case volume or pack propellant against the primer flash hole, thereby presenting no risk of damage to the firearm. These subsonic rounds are pleasant for the recreational shooter and provide a significant advantage in tactical situations where stealth is a requirement.

Projectile Selection. There are several tools and resources that may be used to screen and select a suitable projectile that is stable at subsonic or reduced velocity and with standard rifle twist rates. For example, there are many bullet stability calculators available commercially that take into consideration velocity, bullet length, bullet weight, barrel rate of twist, and projectile diameter that can aid in determining bullet stability. One such bullet stability calculator is titled "Load From a Disk" version 3.0.3 (32bit), Copyright 1996-2001 Wayne Blackwell and Intelligration Systems Group. This software was used to select a projectile for a .223 Remington subsonic cartridge. A Hornady 55 grain FMJ-BT/WC projectile was initially selected for testing with the software. The projectile dimensions (bullet length of .735 inches and bullet diameter of .224 inches), weight (55 grains), the existence of a boat tail base, and the desired muzzle velocity of 1070 feet per second (fps), were entered into the software. The program calculated that this projectile would be stable with an optimum twist rate of 1 turn in 9 inches and a bullet rate of spin of (rev/sec) 1426. Since the standard twist rate for a .223 Remington is 1 turn in 9 inches, this software indicated that the Hornady 55 grain FMJ-BT/WC (full metal jacket, boat tail, with cannelure) projectile will stabilize in commercially available firearms at subsonic velocities.

Another useful bullet stability calculator is the National Firearms Association Bullet Stability Calculator, (Copyright 2002 National Firearms Association, Box 52183, Edmonton, Alberta, T6G 2T5 Canada) available on the internet at http://www.nfa.ca/NFAFiles/CFJArchive/Ballistics/BulletStabilitvCalc.html. This program may be used to select a projectile for .308 Winchester subsonic cartridge. A Hornady 170.0 grain RJM (round nose) projectile was initially selected for testing with the software. The following data was entered into the program: the velocity of 1070 fps, bullet length of .95 inches, bullet weight of 170 grains, standard rifle twist of commercially available .308 Winchester firearms (one turn in 12 inches), and the diameter of the bullet .308 inches. The program then calculates the stability factor of 3.89. A stability factor greater than 1.5 is considered to be stable.

Other known bullet stability calculators are available from Corbin Software, PO Box 2171, 600 Industrial Circle, White City, Oregon 97503 and online at ht ://www.lascmces.com Hbιrι/ballistics/calculations.html.

The foregoing stability calculators are intended to provide an initial screening of projectiles that might be used in subsonic ammunition. It is recommended to test a given projectile using more than one stability calculator. The final selection and optimization can only be made after laboratory and field testing.

Without being bound by theory, it is presently believed that suitable projectiles may be initially selected based on ratios of Diameter and Length. Projectiles with ratios (D:L) of approximately one are better suited for subsonic and reduced velocity projectiles. In addition, projectiles in which the center of mass is approximately equal to the midpoint of the projectile tend to be more stable at subsonic and reduced velocity. Such projectiles may have round or flat points. In addition, the rifle twist rate affects projectile selection. For example, a broader variety of projectiles are stable at higher twist rates. Fewer projectiles are stable when fired from low twist rate rifles.

Also without being bound by theory, another method of stabilizing a projectile is to move the center of pressure behind the center of mass or what is commonly referred to as the center of gravity or CG. One possible way to accomplish this is introducing drag to the rear of the projectile. Introducing angles over 7 degrees on the boat tail is one possible way. In other words, boat tail angles between 7 and 90 degrees will introduce more drag to the rear of the projectile. A boat tail angle of 90 degrees is equivalent to a flat projectile base. Discontinuities of the rear portion of the bullet can increase drag.

Propellant Selection. Propellant or powder selection is important in subsonic ammunition. Firearm manufacturers have set pressure limitations on firearm assemblies. By using fillers or reducing charge volumes of standard propellants to obtain subsonic velocities, pressure can exceed firearm ratings and cause dangerous situations. Therefore, a high level of skill is required to safely use reduced propellant charges.

For standard subsonic ammunition in accordance with the present invention, the propellant may be a moderately fast burning powder, such as a standard pistol powder, to generate adequate pressure to overcome the forces associated with case neck release and initial rifling engagement forces. The term "moderately fast burning powder" is not intended to embrace the very fastest pistol powders. Similarly, it is to be distinguished from fast rifle powders. This is accomplished while retaining just enough pressure to allow the projectile to overcome remaining drag in the bore as well as any gas relief characteristics of firearms and still maintaining subsonic velocities.

Table 2 is a typical propellant burn rate chart. The infoπnation is drawn from the internet website, http://www.reloadammo.coιrι/burnrate.htm (M.D. Smiths Reloading Pages). The chart is courtesy of Hodgdon Powder Company. Table 1 lists qualitative burn rates from fastest to slowest. The actual quantitative burn rate of these propellants is generally proprietary information. Nevertheless, the propellants 1-41 are typically used for pistols and shotgun applications, propellants 42-80 are typically used for small to medium centerfire rifle applications, and propellants 81-107 are typically used for large and magnum centerfire rifle applications. The table is for general information only and one can not assume that each step is incremental in the chart.

Table 2

Propellant Burn Rate Chart

(List from Fastest to Slowest Propellant)

1. R-l Noraia 37. N350, Vihtavuori 73. H-335, Hodgdon

2. N310, Vihtavuori 38. HS-7, Hodgdon 74. BL-C(2), Hodgdon

3. Bullseye, Alliant 39. W-571, Winchester 75. AAC-2460, Accurate

4. N312, Vihtavuori 40. No. 7, Accurate 76. W-748, Winchester

5. Solo 1000, Accurate 41. Blue Dot, Alliant 77. Reloader 12, Alliant

6. Clays, Hodgdon 42. No. 9, Accurate 78. N135, Vihtavuori

7. Red Dot, Alliant 43. 2400, Alliant 79. IMR-4064, IMR

8. N318, Vihtavuori 44. Nl 10, Vihtavuori 80. Varget, Hodgdon

9. Hi-Skor 700X, IMR 45. R-123, Norma 81. AAC-2520, Accurate

10. N320, Vihtavuori 46. H-l 10, Hodgdon 82. N-202, Norma

11. Green Dot, Alliant 47. W-296, Winchester 83. XMR-4064, Accurate

12. International, Hodgdon 48. SR-4759, IMR 84. IMR-4320, IMR

13. No. 2, Accurate 49. N120, Vihtavuori 85. N140, Vihtavuori

14. N321, Vihtavuori 50. XMP-5744, Accurate 86. AAC-2700, Accurate

15. N324, Vihtavuori 51. IMR-4227, IMR 87. Reloader 15, Alliant

16. HP-38, Hodgdon 52. N125, Vihtavuori 88. H-380, Hodgdon

17. W-231, Winchester 53. H-4227, Hodgdon 89. N150, Vihtavuori

18. N325, Vihtavuori 54. Nl 30, Vihtavuori 90. W-760, Winchester

19. N330, Vihtavuori 55. AAC-1680, Accurate 91. H-414, Hodgdon

20. PB, IMR 56. W-680, Winchester 92. Nl 60, Vihtavuori

21. N331, Vihtavuori 57. N132, Vihtavuori 93. IMR-4350, IMR

22. No. 5, Accurate 58. N-200, Norma 94. H-4350, Hodgdon

23. Unique, Alliant 59. N133, Vihtavuori 95. N-204, Norma

24. WSL, Winchester 60. IMR-4198, IMR 96. Reloader 19, Alliant

25. Power Pistol, Alliant 61. H-4198, Hodgdon 97. IMR-4831, IMR

26. Universal, Hodgdon 62. XMR-2015, Accurate 98. XMR-3100, Accurate

27. SR-7625, IMR 63. Reloader 7, Alliant 99. H-450, Hodgdon

28. W-473AA, Winchester 64. Nl 34, Vihtavuori 100. H-4831, Hodgdon

29. Herco, Alliant 65. IMR-3031, IMR 101. MRP, Norma

30. N340, Vihtavuori 66. Benchmark 1, Hodgdon 102. N165, Vihtavuori

31. WSF, Winchester 67. N-201, Noraia 103. Reloader 22, Alliant

32. HS-6, Hodgdon 68. H-322, Hodgdon 104. IMR-7828, IMR

33. W-540, Winchester 69. Benchmark 2, Hodgdon 105. H-1000, Hodgdon

34. 3N37, Vihtavuori 70. AAC-2230, Accurate 106. XMR-8700, Accurate

35. WAP, Winchester 71. IMR-4895, IMR 107. H-870, Hodgdon

36. Hi-Skor 800-X, IMR 72. H-4895, Hodgdon

Computer software may be used to simulate propellant ballistic properties in a given cartridge. This can help in selecting and pre-screening a suitable propellant and determining the quantity of propellant. One such program is called "QuickLOAD - Interior Ballistics Predictor Program" (Copyright 1987-2001 - H. Broenel, Babenhausen Germany), distributed by Nostalgia Enterprises Company, akaNECO, 536C Stone Road, Benicia, CA 94510, http://www.neconos.com/index.html. The software includes data on more than 800 cartridges, 140 powders, and 2000 bullets. Data on other cartridges, powders, and bullets may be manually entered. To use the software, one selects the cartridge, the projectile, and the powder charge. The software will predict muzzle velocity and chamber pressure. It will graph pressure and velocity with respect to barrel position. It can also provide other information, such as the bullet's travel at the time of maximum pressure. It is important to recognize that such ballistic simulation software cannot predict catastrophic events, like using low charges of standard powders accurately, or using extremely fast powders. But the software is useful to provide initial selection and screening, and to provide information on the quantity of propellant to be used. The final selection and optimization is done through field- testing with strain gauges to measure chamber pressure and a chronograph to measure actual velocity.

Several different standard subsonic cartridge assemblies have been prepared, which include, but are not limited to:

1. .223 cartridge - PMC brass, Winchester small rifle primer, 3.9 grains Alliant Unique, Hornady 55 grain FMJ-BT W/C projectile, Cartridge overall length = 2.24 inches.

2. .223 cartridge - PMC brass, Winchester small rifle primer, 4.2 grains WP-1450, Hornady 55 grain Moly FMJ-BT W/C projectile, Cartridge overall length = 2.24 inches.

3. .308 cartridge - PMC brass, Winchester large rifle primer, 8.2 grains Alliant Unique, Hornady 170 grain FP projectile, Cartridge overall length = 2.565 inches.

4. .308 cartridge - PMC brass, Winchester large rifle primer, 8.5 grains WP-1450, Hornady 170 grain RN projectile, Cartridge overall length = 2.565 inches.

5. .300 Winchester Magnum cartridge - PMC brass, Winchester large rifle primer, 14.0 grains Alliant Unique, Nossler 220 grain SSP projectile, Cartridge overall length = 3.332 inches.

6. 7.62 X 39mm cartridge - PMC brass, Winchester large rifle primer, 7.8 grains Alliant Unique, Sierra 180 grain Spitzer projectile, Cartridge overall length = 2.19 inches.

7. .50 BMG cartridge - MI brass, CCI # 35 primer, 35.0 grains WC-1450 [SHOULD IT BE WP-1450?], 647.0 grain FMJ, Cartridge overall length = 5.45 inches.

In general terms, a typical standard subsonic .223 caliber rifle cartridges will contain from 3.5 to 4.5 grains of moderately fast pistol propellant and a projectile weighing from 50 to 60 grains. A typical, a standard subsonic .308 caliber rifle cartridge will contain from 6 to 9 grains of pistol propellant and a projectile weighing from 150 to 220 grains. A typical standard subsonic .50 BMG rifle cartridge will contain from 20 to 60 grains of moderately fast pistol propellant and a projectile weighing from 525 to 900 grains. A typical standard subsonic .300 Winchester Magnum rifle cartridge will contain from 8 to 16 grains of moderately fast pistol propellant and a projectile weighing from 150 to 230 grains. A typical standard subsonic 7.62 X 39mm rifle cartridge will contain from 7.5 to 8.5 grains of moderately fast pistol propellant and a projectile weighing from 170 to 190 grains. Generally, the smaller weight projectile would be used will less propellant.

Byway of comparison, a standard supersonic .223 rifle cartridge contains about 25 grains of propellant. The standard subsonic .223 rifle cartridge within the scope of the present invention contains about 3.5 to 4.5 grains of a moderately fast burning pistol propellant, or about 20%, by weight of the rifle propellant used in a comparable standard supersonic rifle cartridge. In general terms, the standard subsonic ammunition within the scope of the present invention will contain a moderately fast burning pistol propellant which is from about 15% to about 20%, by weight, of the rifle propellant used in a comparable standard supersonic rifle cartridge.

Surprisingly, the reduced quantity of propellant used with the standard subsonic ammunition does not exhibit inconsistent ignition. Unlike prior art attempts, the subsonic ammunition in accordance with the present invention does not require special cartridge inserts, fillers, or casing modifications. Without being bound by theory, it is believed the small quantity of propellant used in the standard subsonic produces consistent ballistic performance with a reduced propellant charge because the propellant undergoes substantially complete combustion within the cartridge casing. In other words, the small quantity of moderately fast burning pistol propellant generates enough gas pressure within the casing off of the initial primer flash to fill the casing with pressure. Sufficient pressure is generated within the casing to expel the projectile at subsonic or reduced velocity.

When fired, the foregoing projectiles traveled at velocities less than 1100 feet per second. The accuracy and penetrating performance of subsonic ammunition prepared according to the above-identified specifications were evaluated:

1. A .223 subsonic cartridge fired from 16 inch Ml 6 with AWC Raider sound suppressor penetrated level III A body armor at 25 yards and 100 yards.

2. A .308 subsonic cartridge fired from 20 inch Remington PSS bolt action rifle with AWC Thundertrap sound suppressor penetrated level III A body armor at 25 yards and 100 yards. 3. A .300 Winchester Magnum cartridge fired from 26 inch HS-Precision bolt action rifle with AWC Thundertrap sound suppressor penetrated level III A body armor at 25 yards and 100 yards.

4. A .223 subsonic cartridge fired from Remington PSS bolt action rifle with AWC Thundertrap sound suppressor accomplished Minute Of Angle "MO A" at 100 yards.

5. A .308 subsonic cartridge fired from Remington PSS bolt action rifle with AWC Thundertrap sound suppressor accomplished Minute Of Angle "MO A" at 100 yards.

6. A .300 Win Mag subsonic cartridge fired from 26 inch HS-Precision bolt action rifle with AWC Thundertrap sound suppressor accomplished Minute Of Angle "MO A" at 100 yards.

The foregoing subsonic ammunition provide accurate projectile trajectory at a range up to about 200-800 yards, depending on the caliber. Lighter projectiles, such as those used with the .223 caliber cartridge, have a shorter range. Heavy projectiles can maintain velocity and accuracy longer.

Cycling subsonic projectiles are selected to be stable at subsonic and reduced velocity using the process described above. However, they are generally heavier projectiles with a longer bearing surface for increased drag within the bore and gas seal in the barrel. In this way, the projectile is expelled more slowly. Lighter projectiles may be used if the brass is crimped about the projectile. If very heavy projectiles are used, such as depleted uranium projectiles, a shorter bearing surface may be used.

Instead of using moderately fast burning pistol propellants, extremely slow burn rate propellants, such as cannon powders, are used. The slow burning propellant combined with a heavy, slower projectile result in a longer resident time within the rifle bore. This keeps pressure high enough to expel the projectile at subsonic velocities and still cycle the action. A light projectile used with slow burning propellant would likely get stuck in the barrel.

1. .223 cartridge - PMC brass, Winchester small rifle primer, 24 grains WP-1840 powder, custom 106 grain projectile (diameter of .224 inches, bearing surface of .825 inches, overall length of 1.078 inches), Cartridge overall length = 2.21 inches. 2. .223 cartridge - PMC brass, Winchester small rifle primer, 18.5 grains WP-

1850 powder, custom 106 grain projectile (diameter of .224 inches, bearing surface of .825 inches, overall length of 1.078 inches), Cartridge overall length = 2.21 inches.

A typical cycling subsonic .223 caliber rifle cartridge will contain from 18 to 25 grains of cannon propellant and a projectile weighing from 90 to 125 grains. The projectile bearing surface may range from .4 to 1.1 inches, and preferably from .8 to .9 inches. Less bearing surface is needed if the projectile is crimped in position. Also, heavy projectiles require less bearing surface.

It will be appreciated that different powders, projectiles, and primers may be substituted for those identified above. For example, the powder "Alliant Unique," which is number 23 in Table 2, is a flake propellant. Flake propellant does not dispense well in automatic loading equipment, or at least at the accuracy tolerances needed to prepare reliable subsonic ammunition in accordance with the present invention. Western Powder WP-1450 is a spherical powder having ballistic properties comparable to Alliant Unique powder. The spherical powder dispenses accurately in automatic loading equipment; the powder selected is preferably a spherical powder. Similarly, the cycling subsonic ammunition examples identified above used WP-1840 and WP-1850 powders, which are spherical powders. A comparable, alternative powder is H-4831, Hodgdon, number 100 in Table 2. Another alternative powder is H-4831SC is not listed in Table 2. H-4831SC is similar to H-4831, except that it is less susceptible to changes in temperature. H-4831 and H-4831SC are extruded propellants that will not dispense well in automatic loading machines. But such propellants could still be used to prepare subsonic ammunition.

It will be appreciated that the present invention provides subsonic ammunition that is accurate, consistent, and reliable, that can use conventional cartridge loading equipment, that can use standard cartridges designed for standard firearm chambers and standard rifle barrels. The present invention also provides subsonic ammunition that is able to cycle the firing mechanisms of automatic and semi-automatic weapons. The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description.

Claims

CLAIMS:

1. A subsonic or reduced velocity ammunition cartridge comprising: a standard rifle cartridge casing having a base end and an open end, sized to be used with a standard rifle having a standard rifle twist rate, said cartridge casing having an internal volume; a primer inserted in the base end of the casing; a quantity of propellant disposed within the casing, wherein the propellant is not a standard rifle propellant; and a projectile sized to fit within the open end of the casing and which is stable at subsonic velocity and at the rifle twist rate.

2. The cartridge of claim 1, wherein the projectile is selected to have a center of mass that is approximately equal to the center of length.

3. The cartridge of claim 1 , wherein the propellant is a moderately fast burn rate pistol propellant.

4. The cartridge of claim 3, wherein the quantity of propellant is in the range from about 15 to 20 %, by weight, of the propellant used in a standard supersonic rifle cartridge using the cartridge casing.

5. The cartridge of claim 1, wherein the propellant is spherical powder.

6. The cartridge of claim 1, wherein the cartridge casing is colored to identify the cartridge as a subsonic ammunition cartridge.

7. The cartridge of claim 6, wherein the cartridge casing is colored black.

8. The cartridge of claim 1, wherein the projectile, when fired from the rifle, travels at subsonic or reduced velocity that stabilizes and maintains sufficient energy to be lethal and penetrate modern body armor.

9. The cartridge of claim 1, wherein the cartridge may be used with a rifle equipped with a sound suppressor.

10. The cartridge of claim 1, wherein the projectile, when fired from the rifle, travels at subsonic or reduced velocity that stabilizes and follows a predictable trajectory.

11. The cartridge of claim 1 , wherein the projectile, when fired from the rifle, travels at subsonic or reduced velocity that stabilizes and follows a predictable trajectory at a range up to about 200-800 yards depending on caliber.

12. The cartridge of claim 1 , wherein the projectile, when fired from the rifle, travels at subsonic or reduced velocity that stabilizes and achieves Minute of Angle at 100 yards.

13. The cartridge of claim 1, wherein the rifle is an automatic or semiautomatic rifle having a cycling firing mechanism, wherein the projectile travels as subsonic or reduced velocity when fired from the rifle, and wherein the cartridge produces sufficient pressure to cycle the firing mechanism.

14. The cartridge of claim 13, wherein the projectile is heavier than a comparable projectile designed for supersonic flight for use with the rifle cartridge casing.

15. The cartridge of claim 13 , wherein the proj ectile has a longer bearing surface than a comparable projectile designed for supersonic flight and use with the rifle cartridge casing.

16. The cartridge of claim 13, wherein the propellant is camion propellant.

17. The cartridge of claim 1, wherein the rifle cartridge is a .223 caliber cartridge containing from 3.5 to 4.5 grains of pistol propellant and a projectile weighing from 50 to 60 grains.

18. The cartridge of claim 1, wherein the rifle cartridge is a .308 caliber cartridge containing from 6 to 9 grains of pistol propellant and a projectile weighing from 150 to 220 grains.

19. The cartridge of claim 1, wherein the rifle cartridge is a .50 BMG cartridge containing from 20 to 60 grains of pistol propellant and a projectile weighing from 525 to 900 grains.

20. The cartridge of claim 1, wherein the rifle cartridge is a .300 Winchester Magnum cartridge containing from 8 to 16 grains of pistol propellant and a projectile weighing from 150 to 230 grains.

21. The cartridge of claim 1, wherein the rifle cartridge is a 7.62 X 39mm cartridge containing from 7.5 to 8.5 grains of pistol propellant and a projectile weighing from 170 to 190 grains.

22. The cartridge of claim 13, wherein the rifle cartridge is a .223 caliber cartridge containing from 18 to 25 grains of cannon propellant and a projectile weighing from 90 to 125 grains.

23. The cartridge of claim 22, wherein the proj ectile has a bearing surface ranging from .4 to 1.1 inches.

24. The cartridge of claim 22, wherein the projectile has a bearing surface ranging from .8 to .9 inches.

25. A method of making a subsonic or reduced velocity ammunition cartridge comprising: obtaining a standard rifle cartridge casing having a base end and an open end, sized to be used with a standard rifle having a standard rifle twist rate, said cartridge casing having an internal volume, wherein a primer is inserted in the base end of the casing; selecting a projectile sized to fit within the open end of the casing which is stable at subsonic or reduced velocity and at the standard rifle twist rate; selecting a moderately fast burning pistol propellant; disposing a quantity of the propellant within the casing, wherein the quantity of propellant is selected to leave substantial void space within the casing internal volume and to generate sufficient pressure upon ignition to expel the projectile at subsonic or reduced velocity; and disposing the projectile within the open end of the casing.

26. A method of making a subsonic or reduced velocity ammunition cartridge that can cycle the firing and loading'action of an automatic or semiautomatic rifle, comprising: obtaining a standard rifle cartridge casing having a base end and an open end, sized to be used with a standard automatic or semiautomatic rifle having a standard rifle twist rate, said cartridge casing having an internal volume, wherein a primer is inserted in the base end of the casing; selecting a projectile sized to fit within the open end of the casing which is stable at subsonic or reduced velocity and at the standard rifle twist rate, wherein the projectile is heavier and has a longer bearing surface than a comparable projectile designed for supersonic flight for use with the rifle cartridge casing; selecting a slow burning cannon propellant; disposing a quantity of the propellant within the casing, wherein the quantity of propellant is selected to generate sufficient pressure upon ignition to expel the projectile at subsonic or reduced velocity and to cycle the firing and loading action; and disposing the projectile within the open end of the casing.