Abstract:
An improved telescoped ammunition round having a projectile comprising an aft recess to receive a booster tube that is affixed to the cartridge case and which remains stationary relative to the cartridge case throughout the firing sequence. The booster tube is provided with a primer to ignite the booster charge and is positioned within the projectile recess to initially propel the projectile and subsequently ignite the main propellant within the cartridge case after the projectile has been forced at least partially into the gun barrel. 
     An improved method of manufacturing such an ammunition round utilizes an aluminum alloy seamless tube as a cartridge case and at least one case end seal. The seal is configured to have a unique angled slot and the case end is conically shaped by a mandrel to be press fit into the seal slot. Once mated in this fashion, the cartridge case and seal are firmly secured to each other. The main propellant and the projectile may be placed within the cartridge case before at least one end of the cartridge case is bent on the mandrel and thus while the case end is straight.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 825,429 filed on Feb. 3, 1986, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an apparatus for improving the ballistic performance of an ammunition round and more particularly, to an improved form of telescoped ammunition with superior and more reproducible interior and exterior ballistics performance. The invention also relates to a unique method for manufacturing such a round using at least one press-fit seal of novel configuration. 
     2. Prior Art 
     Telescoped caseless ammunition is comprised of a propellant charge having an axial bore or cavity, a projectile housed entirely within the axial bore of the propellant charge and a primer positioned aft of the projectile. When a telescoped round of ammunition is loaded into the chamber of a gun, the projectile being housed in a propellant charge is not seated in the barrel of the gun as is the projectile of a round of conventional ammunition when in a gun chamber. Upon initiation of the primer of the telescoped round, the projectile is forced forward into the barrel of the gun and becomes seated in the barrel. The telescoped ammunition concept provides a method of packaging the ballistic components of high performance ammunition that significantly reduces total cartridge volume. This reduced volume can be converted to improved gun and feed system density in volume limited environments. 
     The general concept of telescoped ammunition is old in the art. By way of example, U.S. Pat. No. 4,197,801 and U.S. Pat. No. 4,335,657 disclose alternative configurations for telescoped ammunition rounds. Unfortunately, while such prior art discloses concepts for telescoped ammunition rounds, the particular physical implementations of the respective disclosures suffer from a number of significant disadvantages which render the mass production of such rounds of questionable worth. For example, each such prior art patent discloses the use of a relatively complex interface between the projectile and the remaining components of the ammunition round which significantly increases the cost of the ammunition. More importantly, each incurs significant performance degradation in the form of non-reproducible ballistic performance both within the round and exterior to the round subsequent to the firing of the projectile. By way of further example, one of the disadvantages of the earlier patent which is discussed in the later patent is that the earlier patent teaches using a mechanical action to control the firing sequence of the telescoped ammunition round but that such mechanical action involves the use of a piston which is ejected from the ammunition round when the ammunition is fired. It was of course recognized in the latter patent that the ejection of debris upon firing the round may cause damage to the environment surrounding the gun such as the exterior of an aircraft. The latter patent purports to solve this clear disadvantage of the earlier patent by providing a stop ring for limiting forward movement of the piston beyond a preselected location thereby retaining the piston within the ammunition round. However, such a stop ring merely adds to the complexity of the ammunition round and in any case does not remedy the inconsistent performance of such rounds which is due at least in part to the movement of the piston as a means for utilizing ignition gases to ignite the main propellant. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the aforementioned disadvantages of the prior art by providing a telescoped ammunition round of drastically modified configuration as compared to the prior art. More specifically, this invention recognizes that it is highly advantageous and unique to provide a telescoped ammunition cartridge in which there is no moving piston required in order to initiate forward motion of the projectile before ignition of the main propellant. As a result, the present invention need not incur the disadvantageous piston ejecting action of the prior art nor need it incur the complex structural requirements in order to retain a moving piston within the ammunition after the projectile is fired. Furthermore, providing a telescoped ammunition round in which only the projectile moves during firing, significantly enhances the precision of the interaction between the initial ignition gases and the main propellant charge thereby rendering the present invention a much more consistent and reproducible form of ammunition round. 
     The present invention is characterized by a projectile the aft end of which has a cylindrically-shaped booster tube recess concentrically located relative to the axis of the projectile. The invention also comprises a substantially cylindrical cartridge case containing a propellant grain charge which provides an axial cavity for receiving the projectile and substantially surrounding the projectile with the aforementioned propellant charge. The forward end of the cartridge case has a circular opening adapted to allow passage of the projectile after firing and is provided with a case end cap or seal which is provided with Mylar membrane environmental seal for enclosing the projectile opening to avoid contamination of the propellant grain charge. In one embodiment of the invention, the rear end of the cartridge case is provided with a thickened portion the center of which provides a threaded opening for receiving the novel booster tube of the present invention. In a second embodiment, the rear end of the cartridge case is also provided with an end cap or seal and both seals are readily press-fit onto the case ends which are conically shaped by a mandrel. The booster tube, when threaded into the rear portion of the cartridge case, remains stationary and affixed to the cartridge case throughout the firing process. The booster tube extends into the booster tube recess in the rear end of the projectile and contains a booster charge and a primer for initiating ignition of the booster charge whereby to provide means for initial acceleration of the projectile prior to ignition of the propellant as will be hereinafter more fully explained. The projectile and booster tube are interconnected by means of a plastic split ring which holds the projectile within the cartridge case and is adapted to be sheared upon firing the projectile. 
     This relatively simple and low cost means for interfacing the projectile and the cartridge case makes it possible to provide a boat-tailed shaped end of the rear portion of the projectile which lowers the drag on the projectile. It will be seen hereinafter that upon firing of the projectile in the telescoped ammunition round of the present invention, the booster tube remains fixed relative to the cartridge case and no portion of the booster tube moves with the projectile. Consequently, unlike the prior art there is no piston that moves with the projectile within the interior of the cartridge and it is quite evident that there is also no piston that remains attached to the projectile outside the cartridge case which would also significantly lower the velocity of the projectile. 
     An inventive manufacturing process employs a metal tube cartridge case, such as one made of an aluminum alloy. The end or ends of the tube may be formed into a conical configuration using a die. Each end cap or seal is uniquely configured to be press-fit onto the case end and remain secured thereto by means of an angled slot, the geometry of which resists axial forces which would otherwise separate the seals from the case. The main propellant charge and the projectile may be readily inserted into the cartridge case before at least one end of the case is bent into its conical shape. 
     OBJECTS OF THE INVENTION 
     It is therefore a principal object of the present invention to provide an improved telescoped ammunition round which significantly reduces or entirely overcomes the noted disadvantages of the prior art. 
     It is an additional object of the present invention to provide an improved telescoped ammunition round which utilizes simpler and lower cost components and assembly which has improved performance both interior and exterior to the cartridge case and which solves the piston problem associated with the prior art. 
     It is still an additional object of the present invention to provide an improved telescoped ammunition round wherein the cartridge case normally associated with the projectile in such types of ammunition is provided with means for affixing thereto a booster tube which remains stationary relative to the cartridge case throughout the firing of the ammunition round and further providing a projectile having means for receiving a portion of the booster tube along the aft end thereof for initial acceleration of the projectile upon primer initiation before the main propellant bed is ignited. 
     It is still an additional object of the present invention to provide a unique press-fit seal which is readily installed on the end of the cartridge case after the case end has been bent into a conical shape using a simple mandrel. 
     It is still an additional object of the present invention to provide a unique manufacturing process for a telescoped ammunition round wherein at least one cartridge case seal is press-fit onto the cartridge case. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned objects and advantages of the present invention as well as additional objects and advantages thereof will be more fully understood hereinafter as a result of a detailed description of a preferred embodiment when taken in conjunction with the following drawings in which: 
     FIG. 1 is a partially cross-sectioned plan view of a first embodiment of the ammunition round of the present invention; 
     FIG. 2 is an exploded view of the first embodiment of the present invention illustrating the components thereof: 
     FIGS. 3 through 6 provide sequential illustrations of the operational sequence of the present invention during firing of the ammunition round thereof; 
     FIG. 7 is an isometric view of a second embodiment of the invention; 
     FIG. 8 is a partially cross-sectioned view of the second embodiment; 
     FIG. 9 is an exploded view of the second embodiment; 
     FIGS. 10 through 14 provide sequential illustrations of the manufacturing process of the present invention; and 
     FIGS. 15 through 18 provide various enlarged cross-sectional views of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1 and 2 it will be seen that in a first embodiment the ammunition round 10 of the present invention comprises four principal components, namely, a cartridge case 12, a projectile 16, a booster tube 20 and a case end cap 26. As seen best in FIG. 1, cartridge case 12 is of a generally cylindrical configuration having a thicker end portion 13 which is provided with a threaded aperture 17. However, the majority of the cartridge case 12 is formed of a relatively thin radial skin 15 which terminates at the end opposite thickened end portion 13 in a tapered end 19 which is adapted to receive case end cap 26 in a press fit configuration. The interior of cartridge case 12 forms a cavity 23 which is adapted to receive the propellant grain 14 in which a cylindrical bore 25 is provided to receive the projectile 16. Projectile 16 is generally of a standard low drag profile and thus substantially standard as compared to prior art projectiles used in telescoping ammunition except that the projectile 16 of the present invention is provided with a novel booster tube recess 18 at its aft end. Recess 18 is of a substantially cylindrical configuration and it is positioned axially relative to the longitudinal axis of the projectile as seen best in FIG. 1. 
     Booster tube 20, is as seen best in FIGS. 1 and 2, a generally cylindrically shaped object having a threaded portion 21 of increased diameter adapted to engage the corresponding threaded aperture 17 of the cartridge case 12. Booster tube 20 also has a tube portion 29 which is adapted to extend into the booster tube recess 18 of the projectile 16 and for that purpose is substantially congruent therewith. A booster charge 24 is contained within the tube portion 29 of the booster tube 20 and extends toward the threaded portion 21 of the booster tube 20 through an elongated charge chamber 31 which extends to a primer 34 positioned concentrically within the threaded portion 21. 
     Those having skill in the art to which the present invention pertains will understand that the physical relationship between the booster charged 24 contained within the tube portion 29 of booster tube 20, is channeled through channel 31 to the primer 34 whereby to permit ignition of the booster charge within the booster tube upon activation of the primer to generate the initial acceleration of the projectile 16 before the propellant grain 14 has been ignited. Both the tube portion 29 of the booster tube 20 and the corresponding portion of the booster tube recess 18 within the projectile 16 are provided with matching annular recesses 35 and 36 respectively which are aligned to receive a split ring 22. Split ring 22 is preferably made of a plastic material readily sheared upon firing of the projectile but is also of sufficient strength to secure the projectile to the booster tube within the cartridge case prior to firing of the projectile. The rear surface of projectile 16 adjacent the booster tube recess 18 is provided with a conical recess 38 which enables easy assembly of the ammunition round of the present invention by merely press fitting the projectile over the tube portion 29 of the booster tube 20 until the split ring 22 engages both annular recesses 35 and 36 concurrently as shown best in FIG. 1. 
     The front end of the cartridge case 12 as previously noted is provided with a tapered end 19 which is designed to be press fit into case end cap 26. Case end cap 26 is provided with an aperture to match the cylindrical bore 25 formed by the propellant grain 14. This aperture of the case end cap is preferably provided with a Mylar membrane environmental seal 28 when the ammunition round 10 of the present invention is fully assembled. This prevents contamination thereof during shipping and storage. Environmental seal 28 is automatically removed upon firing the round as a result of passage of the projectile 16 through the cylindrical bore 25 during firing. 
     The firing sequence of the ammunition round 10 of the present invention may be best understood while referring to FIGS. 3 through 6. In each such figure the ammunition round 10 of the present invention is shown positioned adjacent a coaxial gun barrel 30 through which the projectile passes during the firing process. The configuration shown in FIG. 3 is essentially identical to that shown in FIG. 1 illustrating that at the instant the primer 34 is initiated neither the booster charge 24 nor the propellant grain charge 14 has been ignited and the projectile is in its stored configuration relative to the cartridge case 12 and booster tube 20. 
     The configuration of the ammunition round 10 of the present invention illustrated in FIG. 4 corresponds to the point in time subsequent to the initiation of the primer wherein the booster charge 24 has been ignited thereby propelling the projectile away from the booster tube and toward the gun barrel 30 while shearing the split ring 22 to permit separation between the projectile and the booster tube. Furthermore, the configuration of FIG. 4 illustrates the position of the projectile 16 in a sufficiently forward position relative to the booster tube 20 wherein ignition gases 32 have reached the main propellant grain charge 14 to thereby ignite the main propellant grain charge. 
     The configuration illustrated in FIG. 5 corresponds to the point in time of the firing sequence in which the projectile is approximately halfway into the gun barrel 30 and the projectile has begun to obturate as pressure from the main propellant bed 14 ignited by the ignition gases 32 of the booster charge 24, has begun to rise. 
     FIG. 6 illustrates the point in time during the firing sequence in which the majority of the projectile 16 has entered the gun barrel 30 and the projectile is being accelerated by the full gas pressure of the main propellant grain charge 14. Subsequent to the point in time illustrated by FIG. 6 the firing sequence continues in a fairly conventional manner which will be apparent to those having skill in the art to which the present invention pertains and which therefore need not be described herein in detail. It is interesting to note however that as represented in the sequence of FIGS. 3 through 6, the booster tube 20 including the tube portion 29 at all times during the firing sequence remains stationary relative to the cartridge case 12 thereby overcoming the noted deficiencies of the prior art previously discussed. 
     A second embodiment of the present invention and an associated inventive manufacturing process are illustrated in FIGS. 7 to 13 which shall now be discussed. More specifically, referring first to FIGS. 7, 8 and 9 it will be seen that telescoped ammunition round 40 comprises a cylindrical cartridge case 42 and a pair of end caps of seals 44 and 45. A projectile 16 is secured within the case 42 in the same manner described above in regard to the first embodiment. Except for the cartridge case and end seals, the ammunition round embodiment 40 is substantially identical to the embodiment of FIGS. 1-6 and accordingly, like reference numerals are used to identify like parts. 
     The ends 46 of cartridge case 42 are bent into a conical shape as shown best in FIGS. 8 and 9. This conical shape provides the appropriate configuration for mating with seals 44 and 45. More specifically, referring to FIGS. 15-18 it will be seen that seal 44, which provides a booster tube aperture 48 having a threaded portion 50 for receiving the mating threaded portion 21 of booster tube 20, is also provided with an annular inner surface 52 of straight or conical shape. This surface combines with a flat 55 to form a slot 54 the terminus of which extends angularly beyond the flat 55. Similarly, seal 45, which provides an exit aperture 56, is also provided with an annular inner surface 58 of straight or conical shape. This surface combines with a flat 62 to form a slot 60 the terminus of which extends angularly beyond the flat 62. The angle of case ends 46 is typically slightly smaller than the angle of slots 54 and 60 so that a certain degree of material stress is placed on the cartridge case material when the seals are press-fit onto the ends of the cartridge case. By way of example, in one embodiment that has been reduced to practice, the initial angle of the case ends 46 relative to the axis of the case was 43.2 degrees and the angle of the slots in both seals relative to the axis of the case was 47.2 degrees. When the seals are press-fit onto the cartridge case, the angle of the case ends 46 will change to accommodate this difference. However, during the press-fit operation, this angle difference assures that the case ends slide along annular surfaces 52 and 58 respectively, thereby avoiding any inadvertent damage to the cartridge case ends. The force required to mate the seals with the cartridge case ends depends upon the respective materials and the thickness of the case wall. In one such press-fit operation a force of approximately 9,000 pounds was employed. More importantly, the angular orientation between the case ends 46 and the seal slots 54 and 60, assures a firm interconnection between the cartridge case 42 and end seals 44 and 45. This interconnection is sufficiently secure to preserve the seal integrity during handling and firing of the projectile and yet extremely simple to implement using the process of the invention. 
     The process of the present invention is best understood by referring to FIGS. 9-13. It will be understood that although a preferred sequence of steps is disclosed herein, the invention is not necessarily limited by the particular sequence described and various individual steps may be performed in sequences other than that disclosed herein. 
     In a preferred embodiment of the inventive process, the initial step is that of forming one end of a cylindrical tube into an angular or conical end as shown in FIG. 10. The bent or formed end is then interconnected to a seal by pressing such a seal in the manner previously described. This step of the process is illustrated in FIG. 11 wherein aft seal 44 has been press-fit onto bent end 46 of case 42. The main propellant charge 14 and projectile 16 and booster tube are then inserted into the case 42 through the non-bent end 46 of the case as shown in FIG. 12. The projectile and booster tube (previously interconnected) may preferably be inserted before the propellant charge to facilitate easy threading of the booster tube into the seating thread of the aft seal. 
     The other end of the cartridge case 42 may then be formed to provide the angular or conical shaped end 46 as indicated in FIG. 13. The forward seal 45 may then be press-fit onto the case thereby completing the process. The process of the present invention may also be carried out where only a forward independent or non-integral seal is utilized such as for the first embodiment configuration of FIGS. 1-6. Obviously, in this latter case, the initial steps of forming the aft end of the case and pressing on the aft seal would be omitted. Furthermore, it is not necessary in the dual seal embodiment to carry out the aft seal forming and fitting step before the forward seal forming and fitting steps. It may in fact be preferred to first form and fit the forward seal and insert the main propellant charge through the aft end of the case. Furthermore, in the case of this reversed sequence, it may be desirable to press-fit the aft seal with the projectile and booster tube already threaded into the aft seal. Although reference is made herein to a mandrel for forming the conical ends of the case 42, it should be understood that the methods and tools used for forming such a conically-shaped end on a cylindrical tube are well-known in the metal machining and forming art and need not be described herein. 
     It will now be understood that what has been disclosed herein comprises a novel, improved telescoped ammunition round including a projectile having a booster tube recess at the aft end thereof adapted for receiving a booster tube having a booster charge therein connected to a primer, the booster tube being threadably engaged with the cartridge case whereby to remain stationary relative to the cartridge case during the entire firing sequence. Thus the present invention obviates the prior art use of moving pistons as well as the prior art requirement for complex mechanism for retaining a piston within the cartridge case during the firing process. Consequently, the present invention provides a simple but elegant solution to the problems associated with prior art telescoped ammunition rounds thereby providing such a round in a configuration which is less costly to produce and more reliable in performance. 
     Two embodiments of the invention and a novel process for manufacture have been disclosed. One such embodiment and the aforementioned process utilize at least one unique cartridge case end seal which is characterized by an annular slotted surface for a press-fit interconnection with a conically formed end of the case. Such a press-fit feature enables a simple and expedient ammunition round assembly which may be advantageously carried out by the preferred process disclosed herein. 
     Those having skill in the art to which the present invention pertains will now, as a result of the applicant&#39;s teaching herein, perceive various modifications and additions to the invention. By way of example, alternative configurations for the cartridge case/end seal interface as well as other alternative means for assembling the entire round will now become apparent. However, all such modifications and additions are deemed to be within the scope of the present invention which is to be limited only by the claims appended hereto.