Abstract:
The present invention describes an improved cartridged projectile ( 100 ). The cartridged projectile ( 100 ) comprises a projectile ( 110 ) seating at a mouth of a cartridge case ( 130 ). The cartridge case ( 130 ) has a base ( 134 ) that houses a high pressure chamber ( 150 ). A side of the high pressure chamber ( 150 ) is capped by a pressure disc ( 170 ), which is secured onto the base of the cartridge case by a nozzle ring ( 160 ). The nozzle ring ( 160 ) has a tapered or conical surface that allows the pressure disc ( 170 ) to flex, and a surface ( 171 ) of the pressure disc ( 170 ) exterior of the high pressure chamber has intersecting V-shaped grooves ( 172 ). When propellant in the high pressure chamber ( 150 ) is burned efficiently, high pressure gases developing inside the high pressure chamber cause the pressure disc ( 170 ) to rupture at a predetermined pressure along the grooves ( 172 ) so that the gases propel the projectile ( 110 ) out of a barrel at a higher speed of about 100 m/s or more.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to an improved cartridged projectile, which projectile is capable of being projected over an extended range without increasing the amount of propellant. In particular, the invention employs a pressure disc to regulate burning of propellant and then discharging the resultant propellant gases to propel the projectile through a barrel of a weapon to a higher muzzle speed of about 100 m/s or more. 
       BACKGROUND 
       [0002]    Cartridged projectile typically refers to a projectile seated at a mouth of a cartridge case, which contains a propellant. Ignition of the propellant is typically by percussion or electric means. When the propellant burns, it generates high pressure gases within the cartridge case. The high pressure gases are then vented to a low pressure chamber located behind the projectile to eject the projectile from the cartridge case and then propel the projectile through a barrel of the weapon. 
         [0003]    It is known that high pressure containment in the cartridge case is necessary for complete and reliable burning of the propellant. Attempts have been made to provide pressure containment in the cartridge case. For example, U.S. Pat. No. 7,004,074, assigned to Martin Electronics, describes a hemispherical burst cap  14  disposed at the mouth of a cartridge case  12 ; this is shown in  FIG. 1 . An inside surface of the hemispherical burst cap  14  has embossed lines. In use, after the propellant is ignited, pressure in the cartridge case  12  builds up to many atmospheres until the embossed lines on the burst cap  14  rupture. The high pressure gases are then vented in a metered manner through the ruptured burst cap to propel the projectile  10  through the gun barrel. However, it appears that pressure containment of this cartridge case has reached its limit and this cartridged projectile can only reach a conventional muzzle speed of up to about 75 m/s. 
         [0004]    There is a need to provide an improved cartridged projectile that can reach a higher muzzle speed of about 100 m/s or more. A higher speed projectile will have a trajectory that is flatter than a low velocity projectile; this translates to improved accuracy with a higher speed projectile. However, the higher speed projectiles must retain the profiles of conventional projectiles so that they are usable on existing weapons. At the same time, recoil on the weapon must be acceptable for handheld weapons. 
       SUMMARY  
       [0005]    The following presents a simplified summary to provide a basic understanding of the present invention. This summary is not an extensive overview of the invention, and is not intended to identify key features of the invention. Rather, it is to present some of the inventive concepts of this invention in a generalised form as a prelude to the detailed description that is to follow. 
         [0006]    The present invention provides a cartridged projectile, which projectile is designed to be fired out of a barrel of a weapon at a higher muzzle velocity of about 100 m/s or more with a corresponding increase in range without increasing the amount of propellant. 
         [0007]    In one embodiment, the present invention provides a cartridged projectile comprising: a hollow cartridge case extending from a base; wherein said base comprises a high pressure chamber formed therein; a threaded hole in communication with the high pressure chamber, with said threaded hole opening into a low pressure chamber defined by an interior of said cartridge case and a rear end of a projectile seated at a mouth of said cartridge case; and a shoulder between the high pressure chamber and the threaded hole; a nozzle ring with an inner surface comprising a tapered or conical bore, with the narrower end of said tapered bore opening into a discharge hole, so that said nozzle ring is seated in said threaded hole and said discharge hole opens into said low pressure chamber; and a pressure disc disposed between said shoulder and said nozzle ring, with a surface of said pressure disc facing the tapered bore being scribed with intersecting V-shaped cross-sectional grooves. 
         [0008]    In one embodiment of the pressure disc, the pressure disc is round and flat and has a thickness T ranging from about 5% to about 10% of its diameter. The vertex at the base of said V-shaped grooves form an angle ranging from about 30 degree to about 120 degree, preferably about 60 degree. Preferably, the depth d of the V-shaped grooves is substantially half the thickness T. 
         [0009]    In another embodiment, the present invention provides a method of propelling a projectile through a barrel to a higher speed, the method comprising: disposing a high pressure chamber within a base of a cartridge case, which is connected to a rear of said projectile; capping a side of said high pressure chamber with a flat pressure disc, wherein a surface of said pressure disc facing an exterior of said high pressure chamber has intersecting grooves of V-shaped cross-section; and clamping said pressure disc to said base of said cartridge case by a nozzle ring, with an inner surface of said nozzle ring adjacent said pressure disc being tapered or conical; wherein after propellant in said high pressure chamber is ignited, pressure in said high pressure chamber builds up and the pressure disc is allowed to flex into the tapered or conical space of said nozzle ring such that after said propellant is burned, stress concentrations at said V-shaped grooves cause said pressure disc to rupture and high energy gases at the rear of said projectile propel it out of said barrel at a speed of 100 m/s or more. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which: 
           [0011]      FIG. 1  illustrates a known cartridged projectile according to U.S. Pat. No. 7,004,074; 
           [0012]      FIG. 2  illustrates a cartridged projectile according to an embodiment of the present invention; 
           [0013]      FIG. 3  illustrates a sectional view of a cartridge case for use with the projectile shown in  FIG. 2 ; 
           [0014]      FIG. 4A  illustrates a pressure disc according to another embodiment of the present invention;  FIG. 4B  illustrates section view XX of the pressure disc shown in  FIG. 4A ;  FIG. 4C  illustrates another embodiment of the pressure disc; 
           [0015]      FIG. 5  illustrates a ruptured pressure disc of the present invention; and 
           [0016]      FIG. 6  illustrates a sectional view of a cartridge case according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    One or more specific and alternative embodiments of the present invention will now be described with reference to the attached drawings. It shall be apparent to one skilled in the art, however, that this invention may be practised without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals or series of numerals will be used throughout the figures when referring to the same or similar features common to the figures. 
         [0018]      FIG. 2  shows a cartridged projectile  100  according to an embodiment of the present invention. As shown in  FIG. 2 , the cartridged projectile  100  is made up of a projectile  110  connected to a mouth of a cartridge case  130  such that there is a space  120  (shown in  FIG. 3 ) bounded by the mouth of the cartridge case and a rear end of the projectile  110 . The space  120  is referred to as a low pressure chamber. 
         [0019]    As shown in  FIG. 3 , the cartridge case  130  is substantially a hollow cylindrical shell  132  that extends from a base  134 . At a centre of the base  134 , there is a stepped hole  136  piercing through a thickness of the base and extending along a longitudinal axis of the cartridged projectile  100 , with the larger of the stepped hole  136  opening to the outside of the base  134 . From the inside of the cartridge case  130 , there is a flat-bottom threaded bore  138  that is in communication with the stepped hole  136 . The threaded bore  138  receives a pressure containment ring  140 . The inside surface of the pressure containment ring  140  comprises a hole  142  and a threaded hole  144  relatively larger than the hole  142 . Due to difference in sizes of the hole  142  and threaded hole  144 , a shoulder  146  is formed between the hole  142  and threaded hole  144 ; preferably, the hole  142  and threaded hole  144  are substantially coaxial with the longitudinal axis of the cartridged projectile  100 . The threaded hole  144  in turn receives a nozzle ring  160 . The inner surface of the nozzle ring  160  consists of a tapered or conical bore  162  and a discharge hole  164  joined to the smaller end of the tapered bore  162  so that the discharge hole  164  opens into the low pressure chamber  120 . On a face of the nozzle ring  160  that is adjoining the low pressure chamber  120 , there are two diametrally opposed blind holes  166 ; these blind holes  166  are for engagement with pegs on a tool (not shown in the figures) to turn the nozzle ring  160  into the pressure containment ring  140 . Similarly, there are two holes (not shown in the figures) on a front end of the pressure containment ring  140  for engagement with pegs on a tool to turn the pressure containment ring  140  into the base  134  of the cartridge case  130 . Clamped between the nozzle ring  160  and the shoulder  146  is a round, flat pressure disc  170 . The space bound by the pressure disc  170 , surfaces of the hole  142  and base  134  of the cartridge case defines a high pressure chamber  150 . In use, the high pressure chamber  150  is filled with a propellant. 
         [0020]      FIG. 4A  shows a pressure disc according to an embodiment of the present invention. As shown in  FIG. 4A , the pressure disc  170  has a surface  171  that is scribed with V-sectional grooves  172 . In one embodiment, vertex of the V shape of the groove  172  has an angle α of about 60 degrees. Other angles α between about 30 and 120 degrees are also possible. As shown in  FIG. 4A , the grooves  172  form a pattern with three segments intersecting near the centre of the pressure disc  170 .  FIG. 4B  shows a sectional view of the pressure disc  170  along line XX. In another embodiment, the pressure disc  170  is made of brass having a tensile strength of about 470 MPa and an elongation of about 22%; in practice, the elongation may range from about 20% to about 25%. Preferably, the groove  172  has a depth d of substantially half a thickness T of the pressure disc  170 . Generally, the thickness T of the pressure disc  170  ranges from about 5% to about 10% of its diameter depending on the calibre of the cartridged projectile  100 . For example, for a 40 mm projectile, the pressure disc  170  is about 20 mm in diameter and has a thickness of about 1 mm, whilst the discharge hole  164  is about 14 mm in diameter. When assembled, the grooved surface  171  of the pressure disc  170  is facing the tapered bore  162 , i.e. the grooved surface  171  is on the low pressure chamber&#39;s side. 
         [0021]    The stepped hole  136  at the base of the cartridge case  130  is filled with a priming charge. In use, after the priming charge is activated, the propellant in the high pressure chamber  150  burns and pressure builds up rapidly within the high pressure chamber  150 . As a result, the pressure disc  170  is flexed outward into the tapered or conical bore  162 ; this causes the V-shaped grooves  172  on the pressure disc  170  to experience high tensile stresses. By interplay of material of the pressure disc  170 , stress concentrations at the grooves  172 , amount of propellant and volume of the high pressure chamber  150 , the pressure disc  170  is designed to rupture at a predetermined pressure when the propellant is burned completely. From tests on the cartridged projectile  100 , it was observed that rupture of the pressure disc  170  usually started from the centre of the pressure disc  170  where the grooves  172  intersect; as pressure in the high pressure chamber  150  builds up, stress concentrations at the centre of the pressure disc  170  cause stresses at the V-shaped tips of the grooves  172  to reach the tensile stress of the pressure disc and this results in rupture of the pressure disc  170 . The energy of the high pressure gases discharging through the ruptured pressure disc  170  and discharge hole  164  then causes complete rupture of the pressure disc  170  along the grooves  172 . The ruptured centre of the pressure disc  170  is deformed into three outward projecting petals  173 , as shown in  FIG. 5 . The energy of the high pressure gases discharging through the ruptured pressure disc  170  also forces the petals  173  to overlay the surface of the tapered bore  162 . In this way, the petals  173  form a nozzle around the tapered bore  162  and the gases in the high pressure chamber  150  are throttled out through the bore  162 , 164  into the low pressure chamber  120 . With the pressure disc  170  of the present invention, burn efficiency of the propellant is significantly increased; this allowed higher pressure buildup in the high pressure chamber  150 ; together with the effect of the conical bore of the nozzle ring  160  of the present invention, the muzzle velocity of the cartridged projectile  110  reaches or exceeds 100 m/s. 
         [0022]    With a higher muzzle velocity of 100 m/s, the range of the projectile according to the present invention is correspondingly extended from a conventional range of about 400 m to an extended range of about 600 m whilst recoil is still kept at a manageable level for handheld weapons. Table 1 below is an extract of the US Army&#39;s training manual, TOP 3-2-504 showing the firing limitations for hand and shoulder weapons: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Limitations 
               
               
                   
                 Computed Recoil Energy 
                 on Rounds fired 
               
               
                   
                   
               
             
             
               
                   
                 Less than 15 foot-lb (20.3 joules) 
                 Unlimited firing 
               
               
                   
                 15 to 30 ft-lb (20.3 to 40.7 joules) 
                 200 rounds/day/man 
               
               
                   
                 30 to 45 foot-lb (40.7 to 61.0 joules) 
                 100 rounds/day/man 
               
               
                   
                 45 to 60 foot-lb (61.0 to 81.4 joules) 
                  25 rounds/day/man 
               
               
                   
                 Greater than 60 foot-lb (81.4 joules) 
                 No shoulder firing 
               
               
                   
                   
               
             
          
         
       
     
         [0023]    From test firing using the cartridged projectiles  100  of the present invention, recoil energy of about 30 joules was recorded; in contrast, conventional cartridged projectiles fired on the same weapon generate recoil energy of about 19.6 joules. The test data prove that by providing the pressure disc  170  of the present invention, the muzzle velocity of the cartridged projectiles  100  is increased to about 100 m/s with a corresponding increase in firing range to about 600 m yet generating a sustainable recoil energy that allows one to fire about 200 rounds/day with a handheld weapon. 
         [0024]      FIG. 4C  shows a pressure disc according to another embodiment of the present invention. As shown in  FIG. 4C , the pressure disc  170   a  has grooves  172   a  that intersect like a cross. Again, the grooves  172   a  are V-shaped in cross-section. A cross pattern of the grooves results in four petals  173  on a ruptured pressure disc; however, the four petals are not always consistently symmetrical about the centre of the pressure disc  170   a.  Whilst the planar pattern of the grooves  172  does not affect the performance of the cartridged projectile  110 , grooves  172  with 3 radiating segments are preferred. 
         [0025]    From  FIG. 3 , a reader will notice that the rear end of the cartridge case  130  is substantially solid in structure. The cartridge case  130  of the present invention is therefore provided to withstand higher pressure buildup in the high pressure chamber  150  as a result of providing the pressure disc  170 , 170   a . In one embodiment, the pressure containment ring  140  or nozzle ring  160  is made of aluminium. In another, the pressure containment ring  140  or nozzle ring  160  is made of steel. Selection of either material for the containment ring  140  or nozzle ring  160  depends on the weight of material and centre of gravity of the cartridged projectile  100  to achieve predetermined ballistic performance. 
         [0026]      FIG. 6  shows a cartridge case according to another embodiment of the present invention. As shown in  FIG. 6 , the pressure containment ring  140  is integrally formed with the base  134  of the cartridge case  130 . This embodiment helps to reduce both costs and number of parts in the manufacture of the cartridge case  130  and cartridged projectile  100 . 
         [0027]    An advantage of the present invention is that the overall dimensions of the cartridge case  130  remain the same as those of a conventional cartridge case. This means that the cartridge case  130  according to the present invention is suitable to fit with all existing types of projectiles without any need for design modifications. This also means that projectiles fitted with cartridge cases  130  of the present invention can be used with existing weapons and existing production processes need not be drastically changed to produce these cartridged projectiles  100 . 
         [0028]    While specific embodiments have been described and illustrated, it is understood that many changes, modifications, variations and combinations thereof could be made to the present invention without departing from the scope of the invention. For example, the pressure disc  170 , 170   a  may be made of steel having a tensile strength range of about 400 MPa to about 520 MPa and elongation of between about 20% and 25%. In another example, the pressure disc is made from aluminium having similar tensile strength and elongation properties.