Abstract:
Embodiments of the invention include an elongate rifle bullet with a plurality of circumferential grooves having overmolded polymer therein defining embedded polymer rings. Embodiments of the invention include cartridges with propellant and such bullets. In one or more embodiments, the bullet has a body portion and a converging nose portion. The polymer rings have an outer surface that is flush with, that is, conforming to the outer surface of the body. The polymer may have be selected to have a favorable coefficient of friction with respect to the barrel. A feature and advantage of embodiments is that the metal to metal contact between the bullet and the barrel is reduced while not diminishing the ballistic coefficient of the bullet.

Description:
[0001]    This application claims priority to U.S. Provisional Application No. 62/244,588 filed on Oct. 21, 2015, said application is incorporated by reference herein. 
     
    
     FIELD 
       [0002]    The present disclosure relates to low caliber firearm bullets, that is, 0.50 caliber and less, and more specifically, to cartridges and rifle bullets. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Rifle bullets have a conventional elongate shape with pointed tip. The elongate shape adds stability during flight and increases the kinetic energy for a particular bullet size. The elongate shape also increases metal surface area contacting the metal barrel during firing and the metal to metal, barrel to bullet, friction can reduce the muzzle velocity of the bullet. Bullets are known having rearward ends with a boat tail and circumferential grooves, both of which have the effect of reducing the surface area of elongate bullet and the metal to metal engagement and friction. Such grooves in rifle bullets have previously been filled with grease for lubrication between the barrel and bullet. Bullets with grooves filled with grease are not commercially feasible in today&#39;s market. 
         [0004]    Innovations providing even incremental improved performance of bullets would be welcome in the marketplace. Such improved performance would certainly include increasing the muzzle velocity of a bullet without effecting its ballistic coefficient. Providing such improved performance with minimal increase in manufacturing cost would be very advantageous. 
       SUMMARY 
       [0005]    Adding grooves to a low caliber bullet can result in greater muzzle velocity. Such grooves provide less surface area of metal to metal contact between bullet and rifled barrel and can also reduce the needed energy to deform the bullet surface by the barrel rifling, both of which can provide an increase in muzzle velocity. However, providing such grooves can increase the bullet drag in air. Bullets are designed to have minimal decrease in velocity as they travel down range as quantified by a “ballistic coefficient”. The higher the ballistic coefficient the less drag a bullet has traveling down range. It is estimated that each circumferential groove decreases the ballistic coefficient of a rifle bullet by about 3.5%. 
         [0006]    Embodiments of the invention include an elongate rifle bullet with a plurality of circumferential grooves having overmolded polymer therein defining embedded polymer rings. Embodiments of the invention include cartridges with propellant and such bullets. In one or more embodiments, the bullet has a body portion and a converging nose portion, the nose and body being monolithic. In one or more embodiments the nose may be hollow and the body solid. The polymer rings have an outer surface that is flush with, that is, conforming to the outer surface of the body with the same or substantially the same radius. A feature and advantage of embodiments is that the metal to metal contact between the bullet and the barrel is reduced while not diminishing the ballistic coefficient of the bullet. 
         [0007]    In embodiments the outer surface of the polymer rings may have a slight concavity such that when the bullet is deformed by the rifling of the barrel, the polymer flows to an extent to level the concavity when the bullet exits the muzzle. 
         [0008]    The overmolding polymer may be formed of various known polymers such as polyamides, acrylonitrile butadiene styrene (ABS), polyetheretherketone (PEEK), polyetherketone (PEK), polyethylene terephthalate (PET), polyoxymethylene plastic (POM/Acetal), ultra-high-molecular-weight poly-ethylene (UHMWPE/UHMW), various fluoropolymers such as polytetrafluoroethylene (PTFE). The bullet may be heated before the overmolding to increase the adhesion between the polymer and the bullet. The polymer may be chosen to provide a minimal coefficient of friction with respect to the steel barrel. 
         [0009]    In one or more embodiments, the bullet may have a polymer tip inserted in a forward interior cavity of the bullet. The polymer may include a main portion forward of the opening and a tip retention portion filling the interior cavity and having a shape corresponding to the interior cavity to retain the polymer tip in place. In some embodiments, the bullet includes a more steeply tapered forward portion that defines a forward facing annular ridge. The tip retention portion may include an exterior portion which encloses the forward portion of the bullet and fills the forward facing annular ridge to retain the polymer tip in place. 
         [0010]    Embodiments of the invention provide benefits from a rifle bullet with polymer rings and a polymer tip with improved retention characteristics. A feature and advantage of embodiments is that bands may be adhered by the adhesion created during overmolding as well as by the lock provided by the loop, as well as by a mechanical lock in certain embodiments. For example, the groove may include an undercut on the rearward side of the groove, the forward side of the groove, or both. 
         [0011]    Embodiments of the invention are directed to manufacturing bullet by insert-molding bands in circumferential grooves. In one or more embodiments an overmolded tip may also be provided. In one or more embodiments, the bands and tip may be molded in a single operation. In one or more embodiments, the polymer tips may include portions filling external jacket skives reducing external-ballistics drag penalties. 
         [0012]    A feature and advantage of one or more embodiments is a projectile that addresses environmental concerns regarding lead by providing a projectile that includes reduced amount of lead or is free of lead. 
         [0013]    A feature and advantage of one or more embodiments is a projectile that forms an entrance wound when entering a body (such as the body of a game animal or a block of ballistic gel) and forms an exit wound that is larger than the entrance wound upon exiting the body. The relatively large exit wound may cause greater blood loss leading to a faster kill. The increased blood loss may also create a blood trail useful for tracking a wounded animal. 
         [0014]    A feature and advantage of one or more embodiments is a projectile that deforms to an expanded or mushroomed shape while passing through a body (such as the body of a game animal or a block of ballistic gel). In an embodiment, the expanded or mushroomed shape has an overall lateral width and a surface area that is greater than the overall lateral width and the surface are of the undeformed projectile. 
         [0015]    A feature and advantage of one or more embodiments is a projectile that forms multiple pedals while passing through a body (such as the body of a game animal or a block of ballistic gel). In an embodiment, the pedals provide enhanced cutting action. In an embodiment, the pedals increase the overall lateral width and the surface area of the projectile compared to the shape of the projectile before the multiple pedals are formed. A feature and advantage of one or more embodiments is a projectile that folds along localized area of weakness to assume a deformed shape. 
         [0016]    A projectile in accordance with one or more example embodiments comprises a projectile body, a plurality of polymer bands  44  and a polymer tip member  36 . In one or more embodiments, the projectile body includes a tail portion, a nose portion and a barrel engaging portion extending rearwardly between the nose portion and the tail portion. In one or more embodiments, the portions of the projectile body are arranged along a central longitudinal axis. In one or more embodiments, the tail portion has a rearward facing surface defining an XY plane. In these embodiments, the tail portion extends forwardly along the central longitudinal axis of the projectile body between the rearward facing surface and the barrel engaging portion. In one or more embodiments, the central longitudinal axis is orthogonal to the XY plane. In one or more embodiments, the tail portion has a tail radius extending between the central longitudinal axis and an outer tail surface of the tail portion. In one or more embodiments, the tail radius increases as the tail portion extends forwardly along the central longitudinal axis. 
         [0017]    In one or more embodiments, the barrel engaging portion of the projectile body extends forwardly along the central longitudinal axis between the tail portion and the nose portion. The barrel engaging portion has a barrel engaging radius extending between the central longitudinal axis and a barrel engaging surface of the barrel engaging portion. In one or more embodiments, the barrel engaging portion defines a plurality of circumferential grooves  44 . In one or more embodiments, the projectile comprising a plurality of polymer bands  46  with each polymer band  46  being disposed in one of the circumferential grooves  44  defined by the barrel engaging portion. 
         [0018]    In one or more embodiments, the nose portion of the projectile body comprising a forward facing edge defining an opening. In one or more embodiments, the nose portion extends forwardly along the central longitudinal axis between the barrel engaging portion and the forward facing edge. In one or more embodiments, the nose portion has a nose radius extending between the central longitudinal axis and an outer nose surface of the nose portion. In one or more embodiments, the nose radius decreases as the nose portion extends forwardly along the central longitudinal axis. In one or more embodiments, the nose portion has a shape generally corresponding to the shape of an ogive. 
         [0019]    In one or more embodiments, the projectile body comprises a body wall extending between an interior wall surface and an exterior wall surface. In one or more embodiments, the interior wall surface defines an interior cavity and the interior cavity fluidly communicates with the opening defined by the forward facing edge of the nose portion. In one or more embodiments, the interior cavity extends rearwardly from the opening to a cavity end point within the projectile body. 
         [0020]    In one or more embodiments, a core member is disposed inside the interior cavity. In one or more embodiments, the core member comprises a forward facing surface and the core member extends rearward from the forward facing surface to the interior cavity end point within the projectile body. In one or more embodiments, the forward facing surface of the core member and the interior wall surface define a forward portion of the interior cavity. In one or more embodiments, the forward portion of the interior cavity has a cavity radius that decreases as the forward portion of the interior cavity extends forward from the forward facing surface of the core member to the opening. 
         [0021]    In one or more embodiments, the projectile includes a tip member extending through the opening. In one or more embodiments, the tip member has a distal portion extending forward of the opening and a proximal portion extending rearward of the opening. In one or more embodiments, the proximal portion of the tip member has a tip retention radius extending between the central longitudinal axis and a tip retention surface of the proximal portion of the tip member. In one or more embodiments, the tip retention radius increases as the proximal portion of the tip member extends rearward from the opening to the forward facing surface of the core member. 
         [0022]    In one or more embodiments, a method of manufacturing a bullet comprises obtaining a bullet body defining one or more circumferential grooves; inserting the bullet body in a mold, the mold including one or more groove sprues, wherein, upon insertion of the bullet body into the mold, each groove defined by the bullet body is placed in fluid communication with at least one of the plurality of groove sprues; injecting molten polymer into the grooves through the sprues; allowing the polymer to cool forming a plurality polymer bands, each polymer band being disposed in one of the plurality of circumferential grooves; and removing the bullet body from the mold. 
         [0023]    In one or more embodiments, a method of manufacturing a bullet comprising obtaining a bullet body defining one or more circumferential grooves, the bullet body comprising a body wall extending between an interior wall surface and an exterior wall surface, the interior wall surface defining an interior cavity, the interior cavity fluidly communicating with an opening defined by a forward facing edge of the bullet body, the interior cavity extending rearwardly from the opening to a cavity end point within the bullet body, a core member disposed inside the cavity, the core member comprising a forward facing surface, the core member extending rearwardly from the forward facing surface to the cavity end point within the body, the forward facing surface of the core member and the interior wall surface defining a forward portion of the interior cavity, the forward portion of the interior cavity having a cavity radius, the cavity radius decreasing as the forward portion of the interior cavity extends forward from the forward facing surface of the core member to the opening. In one or more embodiments, the method further includes inserting the bullet body in a mold with at least one tip sprue and one or more groove sprues, so that each groove sprue is in fluid communication with one of the one or more circumferential grooves and the forward portion of the interior cavity is in fluid communication with the at least one tip sprue; injecting molten polymer into the one or more grooves through the one or more groove sprues; injecting molten polymer into the forward portion of the interior cavity through the at least one tip sprue; allowing the polymer to cool forming a polymer tip and one or more polymer bands, each polymer band being disposed in one of the one or more circumferential grooves, the polymer tip comprising a forward portion extending forward of the opening and a rearward portion extending rearward of the opening, the rearward portion having a shape corresponding to the forward portion of the interior cavity to retain the polymer tip in place; and removing the bullet body from the mold. 
         [0024]    The above summary is not intended to describe each illustrated embodiment or every implementation of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0025]    The drawings included in the present application are incorporated into, and form part of, the specification. They illustrate embodiments of the present disclosure and, along with the description, serve to explain the principles of the disclosure. The drawings are only illustrative of certain embodiments and do not limit the disclosure. 
           [0026]      FIG. 1  depicts a side elevation view of rifle bullet, according to one or more embodiments. 
           [0027]      FIG. 2  is a cross-sectional view of the bullet of  FIG. 1 . 
           [0028]      FIG. 3  depicts a side elevation view of the bullet body of  FIG. 1  before the overmolding process. 
           [0029]      FIG. 4  depicts a cross-sectional illustrating a bullet and casing and the respective interface according to one or more embodiments. 
           [0030]      FIG. 5  is a cross-sectional view of mold with a bullet therein prior to overmolding polymer bands thereon. 
           [0031]      FIG. 6  is a cross-sectional view of mold with a bullet therein prior to overmolding polymer bands thereon. 
           [0032]      FIG. 7  is a cross-sectional view of mold with a bullet therein prior to overmolding polymer bands thereon. 
           [0033]      FIG. 8  is an exploded perspective view of a bullet in accordance with the detailed description. 
           [0034]      FIG. 9  is an exploded perspective view of a bullet in accordance with the detailed description. 
           [0035]      FIG. 10  is an enlarged perspective view further illustrating the tip member of the bullet shown in  FIG. 9 . 
           [0036]      FIG. 11A  is an enlarged perspective view further illustrating the tip member of the bullet shown in  FIG. 8 . 
           [0037]      FIG. 11B  is an enlarged side view further illustrating the tip member of the bullet shown in  FIG. 11A . 
           [0038]      FIG. 12  is a perspective view showing a projectile body in accordance with the detailed description. 
           [0039]      FIG. 13  is a perspective view of a projectile body in accordance with the detailed description. In the embodiment of  FIG. 13 , the projectile body has been sectioned along a plane YZ and a plane XZ. 
           [0040]      FIG. 14  is an enlarged perspective view of the projectile body shown in  FIG. 13 . 
           [0041]      FIG. 15  is a cross-sectional view of the projectile body shown in  FIG. 13  and  FIG. 14 . 
           [0042]      FIG. 16A  is a side view of a projectile body in accordance with the detailed description. 
           [0043]      FIG. 16B  is a cross-sectional view of the projectile body shown in  FIG. 16A  taken along section line B-B shown in  FIG. 16A . 
           [0044]      FIG. 16C  is a cross-sectional view of the projectile body shown in  FIG. 16A  taken along section line C-C shown in  FIG. 16A . 
           [0045]      FIG. 16D  is a cross-sectional view of the projectile body shown in  FIG. 16A  taken along section line D-D shown in  FIG. 16A . 
           [0046]      FIG. 16E  is a cross-sectional view of the projectile body shown in  FIG. 16A  taken along section line E-E shown in  FIG. 16A . 
           [0047]      FIG. 17A  is a side view of a tip member in accordance with the detailed description. 
           [0048]      FIG. 17B  is a cross-sectional view of the tip member shown in  FIG. 17A  taken along section line B-B shown in  FIG. 17A . 
           [0049]      FIG. 18  is a cross-sectional view of a projectile including a projectile body and a tip member. 
           [0050]      FIG. 19A  depicts a side elevation view of rifle bullet, according to one or more embodiments. 
           [0051]      FIG. 19B  is a cross-sectional view of the bullet shown in  FIG. 19A . 
           [0052]      FIG. 19C  depicts a side elevation view of the bullet body shown in  FIG. 19A  before the overmolding process. 
           [0053]      FIG. 20A  depicts a side elevation view of rifle bullet, according to one or more embodiments. 
           [0054]      FIG. 20B  is a cross-sectional view of the bullet shown in  FIG. 20A . 
           [0055]      FIG. 20C  depicts a side elevation view of the bullet body shown in  FIG. 20A  before the overmolding process. 
           [0056]      FIG. 21A  depicts a side elevation view of rifle bullet, according to one or more embodiments. 
           [0057]      FIG. 21B  is a cross-sectional view of the bullet shown in  FIG. 21A . 
           [0058]      FIG. 21C  depicts a side elevation view of the bullet body shown in  FIG. 21A  before the overmolding process. 
           [0059]      FIG. 22  is a cross-sectional view of an assembly including a cartridge case. 
           [0060]      FIG. 23  is a cross-sectional view of a cartridge including a cartridge case and a projectile. 
       
    
    
       [0061]    While embodiments of the disclosure are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
       DETAILED DESCRIPTION 
       [0062]    Referring to  FIGS. 1-3 , a side view of rifle bullet  20  is depicted according to one or more embodiments. The bullet  20  has a body  22  with a main body portion  24  and a nose portion  32 . In one or more embodiments, the main body portion  24  comprises a tail portion  102  and a barrel engaging portion  104 . Additionally, the bullet  20  may include a polymer tip  36  in a forward cavity  38  of the nose portion  32 . The bullet main body portion and nose portion in one or more embodiments are monolithic. In one or more embodiments, the bullet  20  has one or more circumferentially extending grooves  44 . The grooves having polymer bands  46  therein formed by overmolding. The grooves may have “square” corners but also other shapes including an undercut shape are within the scope of the invention. That is, the cross section of the groove and the band molded therein may be, by way of example and not limitation, trapezoidal shaped in lateral cross-section and/or a C-shape cut. The grooves are contemplated to extend inwardly 4 to 15% of the diameter of the main body portion adjacent to the groove. In one or more embodiments, there pa be 1, 2, 3, 4, or 5 grooves. In one or more embodiments there may be a single groove. In one or more embodiments a monolithic body portion, tail portion and nose portion are formed of unalloyed copper, a copper alloyed with another metal, or other metal. 
         [0063]    Referring to  FIG. 4 , a bullet  20  according to embodiments of the invention is seated in a casing  50 . An upper lip  52  of the casing  50  may be aligned and slightly swaged inwardly at one of the bands whereby a very secure high integrity seal with respect to the interior of the casing and the propellant may be formed. 
         [0064]    Referring to  FIG. 5 , a mold  60  is illustrated with two mold halves  62 ,  64 , and with nozzle ports  70 ,  72  for injection molding molten polymers, and with sprues  76 ,  78 . The sprues  76  leading to the grooves in the bullet body  80  effect the overmolding of the bands in the grooves. The sprue  78  provide the molten polymer for the overmolded tip. In one or more embodiments, the mold wall surface  79  is flush at the location of the grooves and the adjacent body portions. 
         [0065]    As overmolded or inserted, the polymer tip  36  has an exterior surface  84  substantially flush with an exterior surface  86  of the bullet for forming a relatively streamlined or spitzer aerodynamic shape. In one or more embodiments, the front cavity  90  may have an undercut portion  92  for providing a mechanical lock for the tip. 
         [0066]    The bullet may be conventionally formed up to the overmolding process. In the overmolding process, the bullet is put in the mold, the mold is closed, and the polymer is injected into the groove and other recess in the bullet that are being overmolded. 
         [0067]    Once injected, the mold  60  applies a holding pressure to the bullet body  80  and the injected thermoplastic material to reduce potential air pockets and for completely filling the grooves  44  and/or the tip cavity  90  with thermoplastic material. As pressure is applied, the mold and thermoplastic material begin to cool and the thermoplastic material solidifies. In one or more embodiments, cooling is expedited by convection due to coolant flowing through cooling lines  208  inside the mold  60 . The mold is opening and the bullet removed. Sprue pieces may be trimmed from the bullet as needed. 
         [0068]    Referring to  FIG. 6 , a mold  60  comprising two mold halves  62 ,  64  is shown. The mold  60  also includes two nozzle ports  70 ,  72  and sprues  76 ,  78  for injection molding molten polymers. The sprues  76  leading to the grooves in the bullet body  80  effect the overmolding of the bands in the grooves. The sprue  78  provides molten polymer to a tip cavity for forming a polymer tip. In one or more embodiments, the mold wall surface  79  is flush at the location of the grooves and the adjacent body portions. In one or more embodiments, a front cavity  90  defined by the bullet body  80  includes an undercut portion  92  for providing a mechanical lock with the polmyer tip. In overmolding processes, in accordance with one or more embodiments, the bullet body  80  is put in the mold, the mold is closed, and the polymer is injected into the groove(s) and other cavities in the bullet that are being overmolded. Once molten thermoplastic material is injected into the mold  60 , the mold  60  applies a holding pressure to the bullet body  80  and the injected thermoplastic material to reduce potential air pockets and for completely filling the grooves  44  and/or the tip cavity  90  with thermoplastic material. As pressure is applied, the mold and thermoplastic material begin to cool and the thermoplastic material solidifies. In one or more embodiments, cooling is expedited by convection due to coolant flowing through cooling lines the mold. The mold is opening and the bullet removed. Sprue pieces may be trimmed from the bullet as needed. 
         [0069]    Referring to  FIG. 7 , a mold  60  comprising two mold halves  62 ,  64  is shown. The mold  60  also include a nozzle port  74  and sprues  76 ,  78  for injection molding molten polymers. The sprues  76  leading to the grooves in the bullet body  80  effect the overmolding of the bands in the grooves. The sprue  78  provides molten polymer to a tip cavity for forming a polymer tip. In one or more embodiments, the mold wall surface  79  is flush at the location of the grooves and the adjacent body portions. In one or more embodiments, a front cavity  90  defined by the bullet body  80  includes an undercut portion  92  for providing a mechanical lock with the polmyer tip. In the example embodiment of  FIG. 7 , the sprue  76  and the sprue  79  are in fluid communication with one another. Also in the embodiment of  FIG. 7 , the front cavity  90  is in fluid communication with the grooves defined by the bullet body  80  via the sprues  76 ,  78 . 
         [0070]    Referring to  FIGS. 1 through 21C , a projectile  20  comprises a projectile body  100 , one or more polymer bands  44  and a polymer tip member  36 . In one or more embodiments, the projectile body  100  includes a tail portion  102 , a nose portion  106  and a barrel engaging portion  104  extending rearwardly between the nose portion  106  and the tail portion  102 . In one or more embodiments, the portions of the projectile body  100  are arranged along a central longitudinal axis  122 . In one or more embodiments, the tail portion  102  has a rearward facing surface  124  defining an XY plane. In these embodiments, the tail portion  102  extends forwardly along the central longitudinal axis  122  of the projectile body  100  between the rearward facing surface  124  and the barrel engaging portion  104 . In one or more embodiments, the central longitudinal axis  122  is orthogonal to the XY plane. In one or more embodiments, the tail portion  102  has a tail radius  220  extending between the central longitudinal axis  122  and an outer tail surface  320  of the tail portion  102 . In one or more embodiments, the tail radius  220  increases as the tail portion  102  extends forwardly along the central longitudinal axis  122 . 
         [0071]    In one or more embodiments, the barrel engaging portion  104  of the projectile body  100  extends forwardly along the central longitudinal axis  122  between the tail portion  102  and the nose portion  106 . The barrel engaging portion  104  has a barrel engaging radius  222  extending between the central longitudinal axis  122  and a barrel engaging surface  322  of the barrel engaging portion  104 . In one or more embodiments, the barrel engaging portion  104  defines one or more circumferential grooves  44 . In one or more embodiments, the projectile  20  comprising one or more polymer bands  46  with each polymer band  46  being disposed in one of the circumferential grooves  44  defined by the barrel engaging portion  104 . 
         [0072]    In one or more embodiments, the nose portion  106  of the projectile body  100  comprising a forward facing edge  148  defining an opening  150 . In one or more embodiments, the nose portion  106  extends forwardly along the central longitudinal axis  122  between the barrel engaging portion  104  and the forward facing edge  148 . In one or more embodiments, the nose portion  106  has a nose radius  224  extending between the central longitudinal axis  122  and an outer nose surface  324  of the nose portion  106 . In one or more embodiments, the nose radius  224  decreases as the nose portion  106  extends forwardly along the central longitudinal axis  122 . In one or more embodiments, the nose portion has a shape generally corresponding to the shape of an ogive. 
         [0073]    In one or more embodiments, the projectile body  100  comprises a body wall  160  extending between an interior wall surface  162  and an exterior wall surface  164 . In one or more embodiments, the interior wall surface  162  defines an interior cavity  152  and the interior cavity fluidly communicates with the opening  150  defined by the forward facing edge  148  of the nose portion  106 . In one or more embodiments, the interior cavity  152  extends rearwardly from the opening  150  to a cavity end point  154  within the projectile body  100 . 
         [0074]    In one or more embodiments, a core member  240  is disposed inside the interior cavity  152 . In one or more embodiments, the core member  240  comprises a forward facing surface  242  and the core member  240  extends rearward from the forward facing surface  242  to the interior cavity end point  154  within the projectile body  100 . In one or more embodiments, the forward facing surface  242  of the core member  240  and the interior wall surface  162  define a forward portion  252  of the interior cavity  152 . In one or more embodiments, the forward portion  252  of the interior cavity  152  has a cavity radius  226  that decreases as the forward portion  252  of the interior cavity  152  extends forward from the forward facing surface  242  of the core member  240  to the opening  150 . 
         [0075]    In one or more embodiments, the projectile  20  includes a tip member  36  extending through the opening  150 . In one or more embodiments, the tip member  36  has a distal portion  362  extending forward of the opening  150  and a proximal portion  364  extending rearward of the opening  150 . In one or more embodiments, the proximal portion  364  of the tip member  36  has a tip retention radius  228  extending between the central longitudinal axis  122  and a tip retention surface  328  of the proximal portion  364  of the tip member  36 . In one or more embodiments, the tip retention radius  228  increases as the proximal portion  364  of the tip member  36  extends rearward from the opening  150  to the forward facing surface  242  of the core member  240 . 
         [0076]    In one or more embodiments, each circumferential groove  44  is partially defined by a groove root surface  330 . In one or more embodiments, each groove root surface  330  has a groove root radius  230  extending between the central longitudinal axis  122  and the groove root surface. In one or more embodiments, the barrel engaging portion  104  has a barrel engaging radius  222  extending between the central longitudinal axis  122  and a barrel engaging surface  322  of the barrel engaging portion  104 . In one or more embodiments, the barrel engaging portion  104  defines one or more circumferential grooves  44 . In one or more embodiments, each circumferential groove  44  has a groove depth extending between the groove root surface  330  and the barrel engaging surface  322 . In one or more embodiments, the projectile  20  comprising one or more polymer bands  46  with each polymer band  46  being disposed in one of the circumferential grooves  44  defined by the barrel engaging portion  104 . In one or more embodiments, each polymer band  46  has a band thickness extending between the groove root surface  330  and the barrel engaging surface  322 . 
         [0077]    In an embodiment, the barrel engaging radius is between 0.07 inches and 0.25 inches. In an embodiment, the barrel engaging radius is between 0.08 inches and 0.18 inches. In an embodiment, the projectile body is integrally formed from a unitary piece of metal. In an embodiment, the projectile body comprises a metal. In an embodiment, the projectile body comprises copper. In an embodiment, the projectile has a weight between 30 grains and 300 grains. In an embodiment, the projectile has a weight between 50 grains and 200 grains. 
         [0078]    Referring to  FIG. 22  and  FIG. 23 , an ammunition cartridge  400  in accordance with one or more embodiments comprises a case  408  comprising a base portion  422  and a case wall  424  extending forward from the base portion  422  to a forward edge  428  of the case wall  424 . An inner surface  426  of the case wall  424  defines a lumen  430 , the lumen extending rearward from the forward edge  428  toward the base portion  422 . In an embodiment, the base portion  422  and the inner surface  426  of the case wall  424  define a cavity  432  and the cavity  432  fluidly communicates with the lumen  430 . In an embodiment, the inner surface  426  of the case wall  424  defines an opening  434  proximate the forward edge  428  of the case wall  424 , the opening  434  fluidly communicating with the lumen  430 . In an embodiment, a propellant charge  436  is disposed inside the cavity  432  for producing a quantity of propellant gas and a primer housing  438  is disposed in a hole  440  defined by the base portion  422  of the case  408 , a priming material disposed inside the primer housing  438  for igniting the propellant charge  436 . The ammunition cartridge also comprises a projectile  420  comprising a projectile body  100  including a tail portion  102 , a nose portion  106 , and a barrel engaging portion  104  extending rearwardly between the nose portion  106  and the tail portion  102 , the portions of the projectile body  100  being arranged along a central longitudinal axis  122 . In an embodiment, the barrel engaging portion  104  of the projectile body  100  extends forwardly along the central longitudinal axis  122  between the tail portion  102  and the nose portion  106 . In an embodiment, the barrel engaging portion  104  defines one or more circumferential grooves  44 . In an embodiment, the projectile  420  comprises a polymer band  46  disposed in the circumferential groove  44  defined by the barrel engaging portion  104  of the projectile body  100 . In an embodiment, the projectile body  100  is positioned to extend through the lumen  430  defined by the inner surface  426  of the case wall. In an embodiment, the projectile body  100  is positioned so that a plane P defined by the forward edge  428  of the case wall  424  passes through the polymer band  46  disposed in the circumferential groove  44  defined by the barrel engaging portion  104  of the projectile body  100 . In an embodiment, an upper portion of the case wall  424  is swaged or crimped inwardly to form a seal between the case wall  424  and the projectile  420  for closing the opening  434  and preventing fluid communication between the propellant charge  436  in the cavity  432  and an atmosphere outside of the ammunition cartridge  400 . 
         [0079]    The following United States patents are hereby incorporated by reference herein: U.S. Pat. No. 3,881,421, U.S. Pat. No. 4,044,685, U.S. Pat. No. 4,655,140, U.S. Pat. No. 4,685,397, U.S. Pat. No. 5,127,332, U.S. Pat. No. 5,259,320, U.S. Pat. No. 535101, U.S. Pat. No. 6,070,532, and U.S. Pat. No. 8,186,277. 
         [0080]    The following United States patents are hereby incorporated by reference herein: 
         [0081]    U.S. Pat. No.  1080974 , U.S. Pat. No.  1 , 135 , 357 , U.S. Pat. No.  1 , 493 , 614 , U.S. Pat. No.  1 , 328 , 334 , U.S. Pat. No.  1 , 967 , 416 , U.S. Pat. No.  375158 , U.S. Pat. No.  5 , 454 , 325 , U.S. Pat. No.  6317946  and U.S. Pat. No.  7 , 380 , 502 . 
         [0082]    The above references in all sections of this application are herein incorporated by references in their entirety for all purposes. Components illustrated in such patents may be utilized with embodiments herein. Incorporation by reference is discussed, for example, in MPEP section 2163.07(B). 
         [0083]    All of the features disclosed in this specification (including the references incorporated by reference, including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
         [0084]    Each feature disclosed in this specification (including references incorporated by reference, any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
         [0085]    The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any incorporated by reference references, any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed The above references in all sections of this application are herein incorporated by references in their entirety for all purposes. 
         [0086]    Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose could be substituted for the specific examples shown. This application is intended to cover adaptations or variations of the present subject matter. Therefore, it is intended that the invention be defined by the attached claims and their legal equivalents, as well as the following illustrative aspects. The above described aspects embodiments of the invention are merely descriptive of its principles and are not to be considered limiting. Further modifications of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention.