SUBSONIC AMMUNITION FOR SMALL-BORE WEAPONS HAVING A NOVEL PROJECTILE

Abstract: Ammunition for a small-bore weapon operable in the semi-automatic or automatic mode. A round of the ammunition includes a combination of case (12), powder (28) and projectile (24) which enables the projectile to be propelled at subsonic velocity from the weapon to a target while generating sufficient energy to consistently operate the bolt of the weapon and which generates substantially no audible sound during its free flight through air. The projectile (24) of the ammunition is formed from a core (25) including multiple elements (40, 46), each of which is formed from a mixture of heavy metal powder and light metal powder that is densified under high pressure to provide enhanced density of the elements, hence of the core. These elements are incorporated into a light metal jacket (52) by high pressure. A method for the manufacture of the projectile is disclosed.

Description: SUBSONIC AMMUNITION FOR SMALL-BORE WEAPONS HAVING A NOVEL PROJECTILE RELATED APPLICATIONS This application is a continuation-in-part of copending application Serial No. 08/843,450, filed April 16, 1997, entitled: SMALL BORE FRANGIBLE AMMUNITION PROJECTILE, Inventor: Harold F. Beal and a continuation-in-part of copending application Serial No. 08/815,003, filed March 14, 1997, entitled: SUBSONIC AMMUNITION, Inventor: Harold F. Beal. FIELD OF INVENTION This invention relates to ammunition wherein the projectile thereof has a muzzle velocity of less than the speed of sound, i.e. subsonic, as the projectile leaves the weapon and during its free flight to a target. Particularly the invention relates to subsonic ammunition for small-bore weapons, i.e. weapons of 50 caliber or smaller bore and which operate in a semi-automatic or automatic mode. As used herein, the terms "weapon" and "gun" are at times used interchangeably and are to be deemed synonymous unless otherwise indicated or obvious from the context of their use. BACKGROUND OF INVENTION Most commonly, the projectile fired from a weapon, particularly a rifle, leaves the muzzle of the weapon at a speed that is greater than subsonic speed, i.e. at a muzzle velocity of 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 speeds of projectiles tend to reduce the effects of lateral wind forces upon the path of the projectile to its target. Therefore, for accuracy of delivery of the projectile to a desired target, commonly it has been the practice to maximize the quantity of powder used to project a given weight projectile to its target consistent with the permissible pressure for a given weapon. Minimization of projectile weight also has been employed to provide greater projectile velocity. Supersonic muzzle velocities, therefore, are the norm for most small-bore rifles. Pistols, on the other hand, commonly exhibit subsonic muzzle velocities. In the prior art, it is also common to employ noise and/or flash suppressors on either rifles or pistols. These devices function to reduce the sound associated with the explosion of the gun powder in the cartridge and/or the rush of gases from the muzzle of the weapon, but, standing alone, suppressors are neither designed for nor intended to reduce a super sonic velocity bullet fired from a gun to a subsonic velocity, nor do suppressors materially affect noise generated by the movement of a projectile through air. Projectiles traveling at supersonic speeds frequently generate an audible sound during their free flight to the target, a major source of which is wobble (yaw) of the projectile during flight. 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. Under certain circumstances of military operations and/or police operations, it is desirable that the source of the weapon firing a projectile not be identifiable by the sound generated by the traveling projectile. Restricting the velocity of the projectile to a subsonic speed provides only a partial solution to this problem. A round of ammunition (at times synonymously termed a "bullet" or a "cartridge") normally includes a case which includes a primer, a quantity of powder contained within the case, and a projectile held in the open end of the case. Upon the striking of the primer by the firing pin of the weapon there is generated a flame which serves to ignite the powder within the case, generating gases which expand and propel the projectile from the muzzle of the weapon. Normally, the case is geometrically shaped and sized to be contained within the chamber of the weapon, and the projectile is of a diametral dimension which allows it to fit in the breech end of the barrel, and to eventually pass through the barrel upon firing of the round. For many rifles, for example, it is common to make the case of the round of ammunition of a size which will provide for the maximumization of the force with which the projectile is propelled from the weapon to the target. Thus, it is common, for a round for a given caliber weapon, to employ a case which will contain a maximum amount of powder, hence the case has a large diameter relative to the diameter of the projectile employed. Over time, these cases have become the "standard" case for a particular caliber weapon and weapons of this caliber are chambered to accept this standard case. Standards for the shape and size of a cartridge for a given weapon, e.g. a rifle, of a given caliber are established and published by Sporting Arms and Ammunition Manufacturers Institute (SAMI) . In the many instances where the standard cartridge case is of a diameter which is substantially larger than the diameter of the bore of the weapon, that end of the case which receives and holds the projectile of the cartridge is "necked down" to a diameter suitable to engage and hold the projectile in the case. For example, the outer diameter of the case for a 5.56 mm cartridge commonly is approximately .360 inch, and the outer diameter of the projectile thereof is .224 inch. In any event, any portion of the projectile that projects from the end of the case is received within the breech end of the bore of the weapon. In this situation, the circular shoulder developed on the case by the necking-down operation serves as a point of reference for the insertion of the cartridge in the chamber of the weapon. Specifically, the chamber of the weapon is sized and shaped such that, when the cartridge is fully and properly inserted into the chamber, at least the juncture of the necked-down length of the case with the circular base of the shoulder engages the breech end of the barrel. With the cartridge in this position within the chamber, that portion of the projectile which projects outwardly from the end of the case is disposed within the bore of the weapon. Through adjustment of the length of that portion of the projectile which extends from the end of the case, it is possible to select the distance by which the projectile extends into the bore of the weapon. The degree of this adjustment, however, is limited to that amount which will not cause the overall length of the cartridge to be unacceptably outside the SAMI specifications for the cartridge when used in a semi-automatic or automatic weapon. Heretofore, it has been proposed to produce subsonic ammunition which comprises the "standard" case and projectile for a given weapon, e.g. a rifle, and to merely reduce the quantity of powder used to propel the projectile, to that volume of powder which provides only sufficient energy to propel the projectile at a subsonic muzzle velocity. The round of ammunition thus produced is like a standard round of ammunition for its intended weapon, but it is only about 50% or less filled with powder, leaving a substantial portion of the interior volume of the case void of powder. This type of subsonic ammunition is commonly fired as a "single shot" round and is not capable of producing the energy required to operate the bolt of a semi-automatic or automatic weapon. A further major problem with this prior practice for the manufacture of subsonic ammunition relates to the reduced volume of powder within the case of the cartridge and the void volume within the case. Specifically, when the weapon is pointed (aimed) at a downward angle, relative to the horizontal, the powder within the case moves toward the leading end of the case and adjacent to that end of the projectile which is inserted into the case. This serves to form an air gap between the primer and the powder so that when the primer is struck by the firing pin, there is a finite time before the flame from the primer reaches and ignites the powder within the leading end of the case, and a finite time elapsing before the burning powder generates sufficient gases to propel the projectile from the weapon. Conversely, if the weapon is aimed upwardly, relative to the horizontal, the powder within the case moves toward the primer so that upon the firing of the primer there is instantaneous ignition of the powder and relatively quicker build up of the gases which propel the projectile from the weapon. At intermediate angles of aiming of the weapon, relative to the horizontal, there are corresponding intermediate delays in the time required for the projectile to be propelled from the weapon after the firing pin has struck the primer. These degrees of delay are extremely detrimental to the accuracy of delivery of the projectile to an intended target. In some circumstances, the delays in "firing" or "hang-fires" of the weapon have been sufficiently long as to deceive the shooter firing the weapon into believing that they have experienced a misfire. Suspecting a misfire, the shooter may open the bolt of the weapon to eject the suspected faulty round, whereupon the round may explode with obvious serious endangerment to the shooter. In accordance with another aspect of the prior art subsonic ammunition, it has been the practice to use fast- burning powders, e.g. pistol powders. These powders exacerbate the problem of erratic propulsion of a projectile from the weapon by reason of the rapid build up of pressure within the case and the rapid fall-off of the pressure once the projectile leaves the case. As a consequence, the prior art subsonic ammunition fails to provide the energy needed to operate the bolt in a semi-automatic or automatic weapon and/or to lock the bolt in an open position upon the firing of the last round in the magazine. It is known in the art that the energy required to operate the bolt of a weapon intended to be fired in a semiautomatic or automatic mode involves the build-up of gas pressure within the barrel of the weapon to the location of a gas exit port near the muzzle of the barrel, such gas pressure being adequate to operate the bolt mechanism. It is therefore an object of the present invention to provide an improved round of subsonic ammunition for smallbore weapons . It is another object to provide ammunition for a small-bore weapon and which is consistently subsonic in velocity from round to round of the ammunition. It is another object to provide subsonic ammunition which will effectively operate the bolt of an automatic or semi-automatic weapon. It is another object to provide a method for the manufacture of subsonic ammunition for a small-bore weapon, particularly a semi-automatic or automatic weapon. It is another object to provide a novel projectile for subsonic ammunition. It is another object to provide a method for the manufacture of a projectile for subsonic ammunition. Other objects and advantages of the present invention will be recognized from the description contained herein, including the claims and the drawings. SUMMARY OF INVENTION In accordance with one aspect of the present invention there is provided a round of ammunition for a small-bore weapon wherein the projectile of the round exits the muzzle of the weapon barrel at a subsonic velocity and which continues its flight path to a target at less than a sonic velocity without generating identifiable sound associated with the flight of the projectile through air. Additionally, the ammunition provides the energy required to operate the bolt of a weapon fired in the semi-automatic or automatic mode. To this end, the present inventor has discovered that by means of a unique projectile combined with a powder of selected burn rate, in a standard case, there can be attained the objectives of subsonic velocity of the projectile, development of the energy required to operate the bolt of a weapon fired in the semi-automatic or automatic mode and elimination of substantially all sound generated by the projectile during its free flight through air. In accordance with one aspect of the present invention, the projectile of the present invention is maximized in weight for a given length of a projectile for a given caliber weapon. This action preferably takes the form of forming the projectile from high-density metal powders, maximizing the length of the projectile, consistent with intended caliber of the projectile and the twist of the lands in the barrel of the weapon for which the ammunition is intended, and minimizing any variation in the density of the projectile in any given plane normal to the length of the projectile and in a direction radially outward from the longitudinal centerline (spin axis) of the projectile. A benefit from the use of this unique projectile is that when the projectile is inserted in the open end of a standard case for a weapon of the intended caliber, the projectile occupies a substantial portion of the internal volume of the case, thereby diminishing that portion of the internal volume of the case which is available to receive gun powder, thereby permitting the case to be filled to a higher percentage of its void volume. Further, in one aspect of the present invention, the inventor has found that use of a gun powder of medium burn rate provides gas generation at a rate and of a volume which, in combination with the heavy projectile, propels the projectile at a subsonic velocity while generating the energy needed to operate the bolt of a weapon fired in the semi-automatic or automatic mode. In one embodiment of the present invention, maximization of the projectile weight and radial uniformity of density are promoted through the use of a mixture of metal powders that are cold-compacted in a die to produce multiple discrete core elements which are ultimately combined to define a core for the projectile. Specifically, in the process of die-forming of a mixture of metal powders, of the type employed in the present invention at a high pressure, e.g. about 50,000 psi, the density of the product is greater adjacent the opposite ends of the formed product than in the central portion of the length dimension of the product. The present inventor utilizes this feature to produce multiple individual elements of a core and thereafter combines these elements to provide a functionally unitary core which has an overall density (weight) which is greater than is possible to obtain when the core is formed as a single unit. In one aspect of the invention, each of the core elements is formed to its own specific geometry for purposes of the desired combining of the elements into a core for the projectile. The combining of the multiple core elements, in one embodiment, is preferably accomplished by selective insertion of the core portions into a soft metal jacket contained in a die cavity. The jacket employed preferably is cup-shaped, having a closed end and an open end. The jacket commonly is formed by deep drawing a metal blank so that the wall thickness of the jacket decreases from a maximum adjacent the closed end thereof to a minimum thickness adjacent the open end of the jacket. The change in wall thickness of the jacket along its length is of primary importance in approximately that half of the length of the jacket extending from the closed end to the midpoint of the length of the jacket. Within this half of the length of the jacket, the wall thickness varies sufficiently as precludes the full insertion, without the application of substantial force, into this half of the jacket of a core element which is diametrally dimensioned to equal the internal diameter of the other half of the jacket. Thus, in the present invention, the inventor forms a first core element which is cylindrical in geometry and which has a diameter that permits the insertion of the first core element into the interior of that half of the jacket nearest the closed end of the jacket. A second core element is formed which is cylindrical in geometry and which has a diameter that is larger than the diameter of the first core element and which permits the second core element to fit snugly within that half of the jacket length nearest the open end thereof. In a preferred embodiment, the combined lengths of the first and second core elements is slightly less than the total interior length of the jacket so that a portion of the jacket wall adjacent the open end thereof is available for deformation radially inwardly of the jacket to at least partially close the open end of the jacket and capture the core elements within the jacket. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a representation of a rifle cartridge, partly sectioned, depicting various of the features of the present invention ; Figure 2 is an exploded view of the components of one embodiment of a core element employed in the projectile of the present invention; Figure 3 is a side elevation view, in section, of the projectile components depicted in Figure 2 as partially assembled into a projectile; Figure 4 is a side elevation view, in section of the projectile components depicted in Figure 2 as fully assembled into a projectile; Figure 5 is a side elevation view, in section, of one embodiment of a jacket employed in the projectile of the present invention; Figure 6 is an enlarged view of a portion of the jacket depicted in Figure 5, and taken generally along the line A-A of Figure 5; Figure 7 is a representation of a pistol cartridge, partly sectioned, depicting various of the features of the present invention; and Figure 8 is flow chart depicting one embodiment of the method of the present invention. DETAILED DESCRIPTION OF INVENTION In the present invention, a "heavy" projectile is defined as a projectile having a density greater than lead, e.g. about 12 or more g/cc, and a total weight of at least 134 grains, for a 5.56 mm cartridge or a proportional weight projectile for a different size cartridge, such as a projectile of 250 grains for a .308 caliber cartridge and of a density greater than lead. As noted, a preferred powder exhibits a medium burning rate. For the present invention, a "medium burning" gun powder is a gun powder that has a burn rate substantially equal to the burn rate of Hodgdon 380 gun powder. Each of the elements of the present invention is selected in combination with the other elements to obtain consistency of subsonic velocity from round to round of the ammunition and provide the energy required for operating the bolt of a semi-automatic or automatic weapon without the projectile exceeding subsonic velocity, while also substantially eliminating any sound generation associated with the free flight of the projectile through air. One embodiment of the present invention is depicted in the several Figures, and includes a round of subsonic ammunition 10 which includes a generally tubular case 12 having a closed end 14 and an open end 16. Within the closed end 14 there is provided a flame port 18 and a primer 20 contiguous to the flame port. The open end of the case includes a necked down, i.e. reduced diameter, portion 22 that is internally sized to receive therein a projectile 24 having a multipart core 25. Within the case, and between the closed end and the projectile, there is defined a cavity 26 within which there is loaded gun powder 28. The geometry of the case is chosen to conform with industry standards for a given caliber cartridge, e.g. .223 caliber (equivalent to 5.56 mm which is designed to be fired from M-16 automatic weapon, for example) . These standards establish the outer diameter of the case, the overall length of the case, the length of the case from the closed end to the beginning of the shoulder 30 formed between the necked down portion 22 and the body 32 of the case, and the internal diameter of the open end of case, among other aspects of the cartridge. Further, the cartridge must conform to the overall length (OAL) industry standard for the given caliber cartridge. The OAL 34 of the cartridge is measured from end to end of the cartridge, including the projectile. This OAL of a round of ammunition is critical to the successful feeding of the cartridge from a magazine into the firing chamber of a semi-automatic or automatic gun. For purposes of the present description of the invention, a 5.56 mm cartridge is discussed, but it will be recognized that the present invention encompasses other sizes (calibers) of cartridges, particularly .308 caliber cartridges. In accordance with one aspect of the present invention, the projectile 24 of the present invention is of maximized weight for a given caliber. To accomplish this desired aspect, the present inventor provides a projectile which preferably is formed from a blended mixture of a heavy metal powder, such as tungsten powder, and a lighter weight metal powder, such as lead. A portion of the blended powders is cold-compacted in a die into a first solid cylinder 40. As depicted in Figure 2, this first cylinder exhibits greater density adjacent each of its opposite ends 42 and 44, this density gradation along the length of the cylinder being achieved by pressing the powders in the die having a cylindrical cavity at a pressure of at least about 40,000 psi and preferably at a pressure of about 50,000 psi. In order to take advantage of this noted feature of the cold-compacted solid cylinder, the present inventor forms the core 25 of the projectile from at least two individually cold-compacted solid cylinders. Thus, a further portion of the blended powders is likewise cold-compacted into a second solid cylinder 46 which also exhibits greater density adjacent each of its opposite ends 48 and 50. In accordance with one aspect of the present invention, these greater densities adjacent the ends of the first and second solid cylinders 40 and 46 contribute significantly to the overall density of each of the solid cylinders, hence to the overall density of the projectile which is produced from these cylinders. It is to be recognized that in a given weapon having a rifled barrel, a projectile fired from the weapon will be spinning about its longitudinal centerline at a rate which is a function of the twist of the lands inside the bore of the weapon barrel. By way of example, M-16 military rifle employs a one-in-seven twist, meaning that each land completes a full turn within each seven inches of barrel length. Thus, a projectile fired from this weapon at a velocity of 1050 fps will be spinning at a rate of 108,000 rpm. At this rate of spin, any deviation of the center of gravity of the projectile from its longitudinal centerline (i.e. its spin axis) will result in the projectile exhibiting wobble (yaw) during its free flight to a target, hence generation of sound during flight. The present inventor found that in the course of forming the projectile of the present invention, absolute coincidence of the center of gravity of the projectile with its longitudinal centerline (spin axis) is not attainable for projectile that exceed a certain maximum length so that there exists a maximum length of a projectile for a given caliber projectile fired from a given weapon, which will remain sufficiently stable in free flight as prevents the projectile from generating audible sound while in flight. Specifically, it has been found that a projectile of a length greater than about 1.12 inch fired from an M-16 military rifle becomes unstable in flight to the extent that the projectile generates audible sound. This length factor, plus the limitation imposed by the caliber of the projectile, produces a limit on the permissible length of a projectile for a given weapon, thereby limiting the permissible volume of a projectile for the weapon. Accordingly, in the present invention, the overall density of the projectile is important in maximizing the weight of the projectile, but also of importance is the attainment of maximum uniformity of density of the projectile in a direction radially outward from the longitudinal centerline of the projectile, taken in any given plane normal to the longitudinal centerline of the projectile. The absolute density of the projectile of the present invention may vary from plane-to-plane, but, radially about the centerline of the projectile, is substantially uniform in any given plane. In the manufacture of the first and second solid cylinders 40 and 46, preferably each cylinder is formed from tungsten metal powder of about -10 and +70 mesh such as the C and M series available from Osram Sylvania of Morristown, NJ, and lead powder having a mesh of about 325, such as that available from Atlantic Engineers of Bergenfield, NJ. In the mixture, the tungsten powder represents between about 40% and 75%, by weight of the mixture, with the remaining weight of the mixture being lead powder. Other powder mixtures may be employed but at the possible expense of attaining less than maximization of the density of the projectile. Further, a third, or more, powder (s) may be included in the mixture for various purposes such as increasing or decreasing the hardness or frangibility of the projectile. The mixture of these powders is blended and a portion of the blended powders is introduced into the cavity of a die having a cylindrical die cavity. In the die, the mixture of powders is cold-compacted at a pressure of at least about 40,000 psi and preferably at a pressure of about 50,000 psi. Under these pressing conditions, the powder mixture is densified and formed into a hard, self-supporting, solid cylinder. The density of the cylinder, however, is greater adjacent its opposite ends than in the central portion of the cylinder between its opposite ends. As noted, to maximize the density of the projectile core of the cartridge of the present invention, the core is formed from at least two solid cylinders which have been individually formed by cold- compaction in a die. By this means, each of the solid cylinders exhibits two areas of maximized density, ie., the area adjacent each of the opposite ends of the cylinder. The resulting core includes four areas of maximized density, thereby resulting in an overall maximization of the density of the core. To form the projectile, the first and second solid cylinders are inserted into a cup-shaped jacket 52 which is formed by deep drawing of a metal blank. The metal of the jacket is one which exhibits lubricity properties between the projectile and the interior of the gun barrel when the projectile is traveling along the barrel during firing of the weapon. A preferred metal is copper. After being formed, the jacket includes a closed end 54, an open end 56 and a longitudinal centerline 64. Referring to Figures 5 and 6, deep drawing of a metal blank into a jacket produces a jacket which possesses a wall section adjacent the closed end 54 of the jacket which progresses from a relatively thick wall at "A" contiguous to the closed end of the jacket to a less thick wall at "B", the approximate midpoint 58 between the opposite ends of the jacket. The wall thickness "C" of the jacket between the approximate midpoint of the length of the jacket and the open end of the jacket normally does not vary significantly for purposes of the present invention. In a preferred embodiment, the first solid cylinder 40 is formed to an external diameter, d l r which is substantially equal to, but not greater than the internal diameter of the jacket adjacent the closed end thereof so that this cylinder can be inserted into the jacket to a location contiguous the closed end of the jacket. The second solid cylinder 46 is formed to a second diameter, d 2 , which is substantially equal to, but not greater than, the internal diameter of the jacket in the region between the length mid-point and the open end of the jacket. Preferably, the cylinders are substantially equal in length, but it is permissible for one of the cylinders to be slightly longer than the other cylinder if desired. The combined lengths of these two solid cylinders determines the overall length of a core 51 of the projectile. As noted, at least two solid cylinders are employed per each projectile core. More than two cylinders per core may be employed, but more than two cylinders may not contribute sufficiently greater weight to the projectile as justifies the cost associated with producing and processing the additional cylinders . In one embodiment, the jacket is placed in an encompassing die and the first cylinder is inserted into the jacket, followed by insertion of the second cylinder into the jacket in tandem within the first cylinder. Thereupon, the cylinders are placed under high pressure, e.g. greater than about 40,000 psi and preferably about 50,000 psi, and deformed, as by means of a die punch aligned with and parallel to the longitudinal centerline 64 of the jacket, to cause the two cylinders to fill a selected portion of the internal volume of the jacket, leaving an unfilled portion 60 of the jacket. The jacket wall section 68 distal of the second solid cylinder is subsequently folded inwardly toward the longitudinal centerline 64 of the jacket to at least partially close the open end of the jacket and to capture the first and second cylinders within the jacket. In a preferred embodiment, the end 52 of the jacket is not fully closed by the inwardly folded wall of the jacket, thereby leaving a circular opening 66 defined in the end 52 of the jacket which becomes filled with a portion of the powder mixture of the core during the course of the swaging operation. This design feature serves to enhance the dispersion of the projectile upon the projectile striking a target as is well known in the art. Notably, even though the density of each cylinder is nonuniform from end-to-end of the cylinder, in any given plane of the cylinder taken normal to the longitudinal centerline of the cylinder, the density of each cylinder is uniform in a direction radially outward from the longitudinal centerline of the cylinder. That is, within a given plane the density is uniform about the spin axis of the projectile. This aspect of each cylinder is important in establishing the center of gravity of the projectile substantially coincident with the longitudinal centerline of the projectile, (i.e., with the spin axis of the projectile) and thereby reducing the likelihood of the projectile exhibiting yaw during its free flight to a target. In this regard, it is also to be noted that in the process of inserting the cylinders into the jacket, the cylinders are not only sized to fit snugly within the jacket in stacked relationship, but further their respective longitudinal axes are aligned coincidently . To this end, the compressive force applied to the tandemly stacked cylinders in the jacket is aligned with and parallel to the longitudinal centerline of the jacket, hence also aligned with and parallel to the longitudinal centerline of the stacked cylinders. By this means, it is believed that deformation of the cylinders as necessary to cause the cylinders to conform to the internal dimensions of the jacket is limited principally to the radial extremities of the cylinder, leaving the vast bulk of each cylinder radially unchanged, hence retaining the radial uniformity of the density of each cylinder substantially intact. It also is believed that the high pressure employed in forcing the cylinders to conform to the internal dimensions of the jacket tends to reconstitute a substantial portion of any bonding between adjacent powder particles which is disrupted in the course of deformation of the cylinders as they are caused to conform to the jacket interior. These factors are further believed to significantly contribute to the observed absence of sound generation by the projectile during its free flight to a target by reason of the attained degree of coincidence of the center of gravity and the longitudinal centerline of the projectile of the present invention. Cartridges for a 5.56 mm weapon operating in the semiautomatic mode were fabricated and fired to test the velocity of the projectile from each cartridge and the ability of the cartridges to develop sufficient energy to consistently operate the bolt of the weapon. In the manufacture of these cartridges, there was chosen a standard case of brass metal. For each of these cartridges, there was provided a projectile comprising a copper metal jacket which has been deep drawn to a length of 1.100 inch. The wall thickness of the jacket adjacent the closed end thereof ("A") provided an internal diameter of about 0.187 inch at this location. The wall thickness of the jacket tapered from the closed end thereof toward the midpoint of the length of the jacket to a wall thickness ("B") providing an internal diameter of 0.190 inch at this location. The wall thickness of the jacket from the midpoint to the open end thereof did not vary materially for present purposes. The internal diameter of the jacket at its open end was 0.190 inch. To form a core for the projectile, there was formed a first solid cylinder having an outer diameter of 0.187 inch employing a mixture of 60%, by weight, tungsten powder and 40%, by weight, of lead powder. The tungsten powder was of -10 + 70 mesh. The lead powder was of 325 mesh. These powders were blended and a portion thereof introduced into a die having a cylindrical cavity. Within the die, the powder mixture was subjected to cold-compaction (at ambient temperature) under a pressure of 50,000 psi. The overall density of this first cylinder was in excess of 14 gm/cc. A second solid cylinder having an external diameter of 0.190 inch was formed in like manner as the first cylinder. This second cylinder exhibited an overall density in excess of 14 gm/cc. The copper jacket of the projectile was inserted into a die having a cylindrical internal cavity of an internal diameter of 0.224 inch. The first solid cylinder was inserted into the jacket through the open end of the jacket disposed in the die, followed by insertion of the second cylinder into the jacket through the open end thereof, so that these cylinders were stacked in tandem within the jacket. A die punch was inserted into the die to engage and apply pressure to the stacked cylinders in a direction aligned with and parallel to the longitudinal centerline of the jacket. A pressure of 50,000 psi was applied to the stacked cylinders. This pressure deformed the first cylinder, causing this cylinder to conform to and fill that portion of the internal cavity of the die adjacent the closed end thereof. Further, the applied pressure served to consolidate the two cylinders into a functionally unitary core having an overall density in excess of 14 gm/cc and an overall length of 1.040 inch. Some length increase of the jacket occurred. After compression of the cylinders, there remained a length of about 0.030 inch of the jacket wall that extended distally of the core. This wall length was thereafter folded inwardly over the distal end of the core, as by swaging, to partially cover the distal end of the core and to aid in retention of the cylinders within the jacket. In this test, the infolded jacket wall did not fully cover the distal end of the core, leaving a circular area of uncovered core that was substantially concentric with the centerline of the jacket and filled with a portion of the powder mixture. This area served as aid to disintegration of the jacket and/or core upon impact with a target in a manner that is well known in the art. The overall weight of each of the projectiles tested was 134 grains . The case of these cartridges was loaded with a Federal 205 Match primer in the closed end thereof and with 11.2 grains of H 380, a spherical-particle gun powder from Hodgdon Powder Co., followed by insertion of a projectile within the open end of the case, thereby closing the open end and providing an OAL of the cartridge of 2.260 inch. The powder filled approximately 65% of the cavity defined in the case between the primer and the projectile. This powder exhibited a medium burn rate. In addition to its other properties, this powder exhibits consistent burn properties at temperatures of between about 0° and about 125° F. Like cartridges were prepared employing other gun powders, having either a slower and faster burn rate than the H-380 powder. These latter cartridges, along with the cartridges which included the H 380 powder, were fired from an M-16 (5.56 mm) weapon operating in the semi-automatic mode. The barrel length of the weapon was 14.5 inches. At least ten rounds of cartridges made from each of these powders were fired. The muzzle velocities of the several cartridges were monitored employing standard chronograph techniques. Only the cartridges made with the slowing burning H 380 powder consistently provided subsonic velocities of the projectiles thereof as evidenced by all 10 of the rounds exhibiting subsonic velocities of their projectiles and successful operation of the bolt of the weapon on every round, including the final round which is intended to lock the bolt in its open position. In each set of 10 rounds of the cartridges made up with the powders other than H 380, there was one or more rounds which exhibited a sonic velocity, failed to successfully operate the bolt of the weapon, or the standard deviation between the velocities of the 10 rounds varied uncontrollably between about 50 to about 200 fps . The rounds made up from the H 380 powder provided a standard deviation of less than 20 fps . The large variation in the standard deviation exhibited by those powders that were slower or faster burning than the H 380 powder is unacceptable for reliable-firing subsonic ammunition. Like cartridges were fired with like results from a M-16 weapon having a 20 inch barrel. In all tests in which the present projectiles, employing H 380 powder, were propelled at a subsonic velocity, there was no audibly detectable sound generated by the projectile due to its movement through air. Further cartridges were made up using the H 380 powder and projectiles having less weight and tested as above. Specifically, projectiles having weights of 100, 115 and 126 grains were made and tested. None of these cartridges fired consistently subsonic with a standard deviation within an acceptable range. Cartridges containing 134 grain projectiles and made up using H 380 powder were fired from the M-16 weapon having a suppressor attached to the muzzle of the barrel thereof. The projectiles from these cartridges also consistently were subsonic in velocity and exhibited an acceptable standard deviation. The cartridges further successfully operated the bolt of the weapon. Moreover, the total sound emanating from the firing of the weapon was almost nonexistent. No audibly detectable sound was generated by the flight of these projectiles through the air. In one embodiment of the present invention, the projectile may be made to be readily frangible upon impact with a solid or semi-solid target. To this end, there may be incorporated into the mixture of tungsten and lead powders, up to about 0.10%, by weight of a micronized polyolefin wax such as ACumist 12 available from Allied Signal, Inc., of Morristown, NJ. This powder has a mesh of -250 + 400 and is also identified as a fine particle size oxidized polyethylene homopolymer. This powder has been found to inhibit bonding of the metal powder particles to one another and therefore, in the noted small quantities, does not materially adversely affect the formability or acceptable strength properties of a solid cylinder that is die-formed in the manner set forth hereinabove. A micronized polyolefin wax and metal powders mixture, when formed into a projectile core encased in a light metal jacket provides a projectile which performs in all material respects like a projectile formed from only the metal powders, except with respect to the frangibility of the projectile when it strikes a target. The degree of frangibility of the projectile is a function of the quantity of micronized polyolefin wax employed, but should not exceed about 0.10%, by weight, in order to obtain a sufficiently strong, self-supporting cylinder. With reference to Figure 7, the present invention further contemplates a round of pistol ammunition 80 including a case 82 having a projectile 84 inserted in the open end thereof. The projectile 84 includes first and second core elements 86 and 88 which have been independently die formed and thereafter die-pressed into a jacket 90 as described hereinabove. One embodiment of the method for producing a projectile in accordance with the present invention is depicted in Figure 8 and includes the steps of selecting tungsten and lead powders and blending these powders into a mixture. A portion of these blended powders is die-formed into a first core element and a further portion is die-formed into a second core element. These two core elements are thereafter inserted into a jacket that is loaded in a die. The core elements in the jacket are pressed into the jacket with a pressure sufficient to cause the core elements to conform to and at least partly fill the interior volume of the jacket. Thereafter, the open end of the jacket, containing the dual core elements, is at least partially closed. Finally, the projectile is recovered for subsequent incorporation into a round of ammunition. Whereas specific examples of the components of the ammunition of the present invention have been given, it is to be understood that a person skilled in the art, given the present disclosure, may elect to employ other equivalent components. Accordingly, it is intended that the invention be limited only in accordance with the claims appended hereto.

Claims: WHAT IS CLAIMED: Claim 1. A round of ammunition for a small-bore automatic or semi-automatic weapon which exhibits subsonic velocity during firing from the weapon and flight to a target, which produces substantially no audibly detectable sound by reason of the movement of the projectile through air during its free flight to a target, and which produces sufficient energy within the weapon to operate the reciprocating bolt of the weapon comprising a generally cup-shaped case having a closed end adapted to receive a primer therein and having an open end, said case having a geometry suitable for the receipt of the case within the chamber of the weapon, a projectile disposed within the open end of said case, said projectile closing said open end of said case and in combination with said case, defining a cavity within said case, said projectile comprising a mixture of a heavy metal powder and a relatively light metal powder, said mixture being cold-compacted to an overall density greater than the density of lead, a quantity of gun powder disposed within said cavity intermediate said projectile and the closed end of said case, said quantity of gun powder being sufficient in quantity and burn rate to propel said projectile from said weapon at a muzzle velocity of not greater than the speed of sound under the existing ambient conditions of temperature and pressure, and further being sufficient in quantity and burn rate, subsequent to firing of the powder, to develop a continuing gas pressure within the barrel of the weapon that is sufficient to operate the bolt mechanism of the weapon, said continuing gas pressure being present along the length of the barrel of the weapon to at least the location of the gas exit bore through which pressurized gas exits the barrel for operation of the bolt mechanism of the weapon. Claim 2. The invention of Claim 1 wherein said round of ammunition is sized to be fired in a 5.56 mm weapon. Claim 3. The invention of Claim 2 wherein the weight of the projectile is at least 134 grains. Claim 4. The invention of Claim 3 wherein the powder is Hodgdon 380 or its equivalent in burn rate. Claim 5. The invention of Claim 1 wherein said heavy metal is tungsten powder and said relatively light metal powder is lead. Claim 6. The invention of Claim 1 wherein said mixture of powders is cold-compacted within a die. Claim 7. The invention of Claim 1 wherein said compacted mixture of metal powders is encased in a light weight metal covering having gun barrel lubricity properties. Claim 8. The invention of Claim 1 wherein said mixture of metal powders includes a further powder which inhibits bonding of the said metal powders to one another. Claim 9. The invention of Claim 8 wherein said further powder comprises micronized polyolefin wax. Claim 10. The invention of Claim 9 wherein said further powder comprises a fine particle size oxidized polyethylene homopolymer or the chemical and physical equivalent thereof. Claim 11. A round of subsonic ammunition comprising a projectile including a metal jacket having a closed end, an open end, an internal volume, a longitudinal centerline and exhibiting lubricity properties with respect to the barrel of a gun, a core contained within said jacket, said core including first and second elements, each of said elements having opposite ends and being formed from a mixture of a heavy metal powder and a lighter metal powder that is cold-compacted into a geometrical shape suitable for being received in said jacket, each of said elements exhibiting greater density thereof adjacent its opposite ends than its density adjacent a location equidistant between its opposite ends, said first and second elements being inserted into said jacket in stacked relationship to one another and subjected to a pressure to cause said elements to conform to and at least partially fill the jacket. Claim 12. The round of ammunition of Claim 11 wherein said jacket is incompletely filled by said elements and includes a portion of the length of said jacket folded inwardly toward said longitudinal centerline of said jacket to at least partially close said open end of said jacket. Claim 13. The round of ammunition of Claim 11 wherein the density of each of said first and second elements adjacent the opposite ends thereof is greater than the density of lead. Claim 14. The round of ammunition of Claim 11 wherein said first metal powder is tungsten metal powder. Claim 15. The round of ammunition of Claim 11 wherein said lighter metal powder is lead. Claim 16. The round of ammunition of Claim 11 wherein said projectile is suitable for firing from a 5.56 mm weapon and possesses a weight of not less than about 134 grains . Claim 17. The round of ammunition of Claim 11 wherein each of said elements is cold-compacted in a die at a pressure of greater than about 40,000 psi.

Inventors: BEAL HAROLD F, BEAL, HAROLD, F.
Applicants: COVE CORP, COVE CORPORATION
Application year: 1998
Main classification: F42B
IPC codes: F42B12