Abstract:
A bullet has a cylindrical body portion and a conical tip monolithically formed with the body portion. The bullet is hollowed out to form an internal cavity. A sidewall defines the structure of the body portion and the conical tip. Bullet structure provides for a bore size, low weight, high velocity, and low recoil projectile having a full-bore size that does not have to expand to a larger diameter during firing in order to transfer its energy to a larger wound channel. In one embodiment, a plurality of recesses is provided on the body portion and extends through the sidewall. The recesses are disposed circumferentially in the radial direction and are offset longitudinally along a longitudinal axis of the bullet. The internal cavity includes a plurality of trusses extending in a radial direction. Instead of or in addition to, the trusses, the wall of the internal cavity may include one or more ridges.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the United States national phase of International Application No. PCT/US2012/071892 filed Dec. 28, 2012, and claims priority to U.S. Provisional Application No. 61/580,751 filed Dec. 28, 2011, the disclosures of which are hereby incorporated in their entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, in general, to an ammunition round for use with rifled or non-rifled barrels, and more particularly, to a hollow bullet adapted for use as a slug projectile. 
     2. Description of the Related Art 
     Regardless of whether used in hunting, military, or law enforcement applications, conventional bullets utilize a cartridge structure, where the projectile (or a plurality of projectiles) and its propellant are encased in a single package. The external dimension of a bullet cartridge and/or the projectile is dimensioned such that its outer dimension is nominally the same as the internal diameter of the rifle or gun barrel. This is a necessary design consideration in order to create a seal between the bullet and the barrel for preventing the escape of gas generated by the propellant once it is fired. Most conventional bullets are specifically designed for use with either rifled or non-rifled barrels. Bullets for use in rifled barrels usually have a solid core with a surrounding metal jacket. Typically, the solid core is made from a relatively heavy metal, such as lead, and the jacket is made from a harder material that is capable of withstanding higher temperature, such as copper. In this manner, the copper jacket of the bullet is slightly compressed during its passage down the barrel by the helical grooves in the rifled barrel. The bullet is spun by the grooves to stabilize its flight. Jacketed bullets are capable of withstanding high firing velocities and can achieve high accuracy over long firing ranges. 
     Certain bullet designs utilized with rifled barrels may have a hollow projectile that has a pit or hollowed-out shape at its tip. Generally, these types of bullets are intended to cause the bullet to fragment upon impact, such that most of the bullet&#39;s kinetic energy is expended upon impact. When a bullet of this kind strikes a target, the bullet widens at its tip to increase the frontal surface area of the bullet and limit its depth of penetration. Other collapsible bullet designs have cutout portions which collapse and expand once the bullet strikes a target. Within the prior art, U.S. Pat. Nos. 1,084,342; 1,084,343; and 1,081,616 to Johnson illustrate this type of bullet. These types of bullets feature openings that have portions of the core extruded out and have a tip portion that is prevented from rotational or longitudinal movement until the inner part of the tip near the extruded portions is weakened upon impact to allow for a “mushrooming” effect. 
     Regardless of whether the firing weapon has a rifled or non-rifled barrel, an important design consideration in making bullets is maximizing the external diameter of the bullet with respect to the inner diameter of the barrel without creating excessive friction during firing. A considerable amount of energy created by the propellant being fired is lost through the friction of the bullet as it travels through the barrel. The friction generates a significant amount of heat and exerts a tremendous pressure on the bullet as it travels through the barrel. One solution for coping with the high temperature and pressure is to use a metal jacket that is capable of withstanding these factors. While this solution is easily applicable to bullets having a solid internal core, it is less practical for use with bullets having a hollow internal structure. In such case, the high pressure exerted on the bullet is sufficient to deform the portions between the hollowed spaces, regardless of whether a metal jacket is used. A bullet that is deformed after it exits the weapon barrel is subject to unpredictable aerodynamics, which reduces its accuracy. Moreover, a bullet that is deformed while traveling within the weapon barrel can often cause internal damage to the helical grooves in the barrel or, at worst, cause the barrel to bulge or burst. 
     Within the art of shotgun-fired ammunition, conventional shotgun slug designs are typically based on a solid lead core positioned within a plastic shell casing. The interior of the shell casing is filled with powder and buffer material. In some embodiments, the solid lead core may be positioned within a sabot. Conventional shotgun slugs do not have a hollow internal structure. 
     With reference to  FIG. 1 , a hollow bullet  10  in accordance with a prior art embodiment is shown. Bullet  10  has a cylindrical body portion  20  and a conical tip  30  monolithically formed with body portion  20 . Conical tip  30  may have a pointed terminal surface  40 . Alternatively, the conical tip  30  may terminate at a blunt surface. A recess  50  is provided on conical tip  30  and extends through the entire conical tip  30  to form a hollow internal cavity  60 . Internal cavity  60  is entirely void of any structure extending across its interior. Such bullet design is described in U.S. Pat. Nos. 1,084,342; 1,084,343; 1,081,616, all to Johnson. 
     A major disadvantage of such design is that the high pressure exerted on bullet  10  during firing is sufficient to deform conical tip  30 . This collapses the recess  50  and deforms the bullet  10  before it exits the barrel and occurs regardless of whether a metal jacket is used. As noted above, bullet  10  that is deformed after it exits the weapon barrel is subject to unpredictable aerodynamics, which reduces its accuracy. Moreover, bullet  10  that is deformed while traveling within the weapon barrel can often cause internal damage to the helical grooves in the barrel or, at worst, cause the barrel to bulge or burst. 
     It will readily be appreciated by those skilled in the art that the problems associated with existing bullet designs with hollow internal structure call for a solution that is not readily available within the prior art. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, a need exists for an ammunition round having a hollow bullet structure with an internal support structure that eliminates the problems commonly associated with prior hollow bullet designs. A further need exists in the art for an ammunition round having a hollow bullet structure that is adapted for use as a slug projectile. An additional need exists for providing an ammunition round that is easy and cost-efficient to manufacture and achieves superior firing characteristics compared to conventional designs. 
     As described in detail herein, an ammunition round for use with a weapon having a rifled barrel may include a cartridge having a generally cylindrical form including a closed bottom portion, an open top portion, and a cartridge sidewall extending circumferentially therebetween. The ammunition round may further include a primer provided at the terminal end of the closed bottom portion for interacting with a firing pin of a weapon. A powder charge may fill at least a portion of an interior of the cartridge between the open top portion and the closed bottom portion. The ammunition round may further include a bullet provided at the open top portion of the cartridge, the bullet enclosing the open top portion of the cartridge. The bullet may include a hollow, cylindrical body portion and a conical tip monolithically formed with the body portion. The body portion and the conical tip may define an internal cavity. The cylindrical body portion may include a recessed portion extending radially inward into a sidewall of the cylindrical body portion to reduce an area of contact between the bullet and a barrel of a weapon. The ammunition round may further include a truss filling at least a portion of the internal cavity to reinforce the internal cavity of the bullet. The truss may be formed from a polymeric material. A part of the cylindrical body portion that extends past the recessed portion may form a driving band. A leading edge of the driving band proximate to the conical tip transitions into a radius of the conical tip. 
     In another embodiment, a bullet for use with a weapon having a barrel may include a hollow, cylindrical body portion and a conical tip monolithically formed with the body portion. The body portion and the conical tip may define an internal cavity. A plurality of recesses may be provided on at least one of the body portion and the conical tip. The plurality of recesses may extend at least partially through a sidewall of the bullet. In addition, at least one truss may extend radially across the internal cavity. The recesses may disposed circumferentially in the radial direction of the bullet and are offset longitudinally along a longitudinal axis of the bullet. In one embodiment, the plurality of recesses may extend fully through the sidewall of the bullet. In another embodiment, the plurality of recesses may be disposed circumferentially in a radial direction of the body portion and are offset longitudinally along a central axis of the bullet. The at least one truss may include a plurality of spokes extending radially outward from a central portion to the interior portion of the sidewall. The bullet may further include at least one ridge extending radially inward within the internal cavity from a central axis of the bullet. The at least one ridge may be located in a transition portion between the body portion and conical tip. A bottom end of the body portion of the bullet opposite the conical tip may be enclosed. The conical tip may terminate at a pointed tip. 
     According to one embodiment of the invention, a bullet may include a hollow, cylindrical body portion and a conical tip monolithically formed with the body portion, such that the body portion and the conical tip define an internal cavity. The cylindrical body portion may include a recessed portion extending radially inward into a sidewall of the cylindrical body portion to reduce an area of contact between the bullet and a barrel of a weapon. The bullet may further include a truss filling at least a portion of the internal cavity to reinforce the internal cavity of the bullet. The truss may be formed from a polymeric material. A part of the cylindrical body portion that extends past the recessed portion may form a driving band. A leading edge of the driving band proximate to the conical tip transitions into a radius of the conical tip. 
     The ammunition round may be adapted for use with a weapon having a rifled or non-rifled barrel. In an embodiment where the ammunition round is adapted for use with a rifled barrel, the bullet desirably has a pointed conical tip and is crimped along the open top portion of the cartridge such that the pointed conical tip protrudes from the cartridge. In an embodiment where the ammunition round is adapted for use with a firearm with a tubular magazine where one round is loaded against the base of another, the bullet desirably has a flattened tip and is crimped along the open top portion of the cartridge such that the flattened tip does not protrude from the cartridge. 
     Further details and advantages of the present invention will become apparent from the following detailed description read in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a hollow bullet according to a prior art embodiment; 
         FIG. 2  is a side view of a bullet and a corresponding cartridge in accordance with an embodiment of the present invention; 
         FIG. 3  is a perspective view of the bullet illustrated in  FIG. 2 , shown without the corresponding cartridge; 
         FIG. 4  is a perspective view of the bullet shown in  FIG. 2 , showing part of the bullet cut away from the bullet body; 
         FIG. 5  is a side view of the bullet shown in  FIG. 2 ; 
         FIG. 6  is a perspective view of a bullet in accordance with another embodiment of the present invention, showing part of the bullet cut away from the bullet body; and 
         FIG. 7  is a side view of a bullet and a corresponding cartridge in accordance with another embodiment of the present invention. 
         FIG. 8  is a side view of a bullet and a corresponding cartridge in accordance with another embodiment of the present invention. 
         FIG. 9  is a side view of a bullet in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For purposes of the description hereinafter, spatial orientation terms, as used, shall relate to the referenced embodiment as it is oriented in the accompanying drawing figures or otherwise described in the following detailed description. However, it is to be understood that the embodiments described hereinafter may assume many alternative variations and configurations. It is also to be understood that the specific components, devices, and features illustrated in the accompanying drawing figures and described herein are simply exemplary and should not be considered as limiting. 
     Referring to the drawings in which like reference characters refer to like parts throughout the several views thereof, an embodiment of a hollow bullet is generally described hereinafter. Referring to  FIG. 2 , a bullet  100  and a corresponding cartridge  110  are shown in accordance with an embodiment of the present invention. Bullet  100  and its corresponding cartridge  110  constitute a single ammunition round  120 . In this embodiment, ammunition round  120  is adapted for use with a weapon having a rifled or non-rifled barrel in a single-shot or a stacked-round magazine configuration. Cartridge  110  has a generally cylindrical form including a closed bottom portion  130 , an open top portion  135 , and a cartridge sidewall  140  extending circumferentially therebetween. In this embodiment, cartridge  110  is desirably constructed from a metallic material, or a specially-formulated plastic material. A primer  150  is located at the terminal end of closed bottom portion  130  for interacting with a firing pin of a weapon (not shown). The interior of cartridge  110  is filled with a charge  155  in form of a powder. Bullet  100  is provided on open top portion  130  such that the cartridge  110  encloses at least part of the bullet  100  and forms round  120 . 
     With reference to  FIGS. 3-5 , bullet  100  is shown without the corresponding cartridge. Bullet  100  has a cylindrical body portion  160  and a conical tip  170  monolithically formed with body portion  160 . Conical tip  170  may have a blunt terminal surface  180 . Alternatively, the conical tip  170  may terminate at a point. The interior of body portion  160  and conical tip  170  is hollowed out to form an internal cavity  190 . A sidewall  200  having a uniform thickness defines the structure of body portion  160  and conical tip  170 . In another embodiment, sidewall  200  may have a non-uniform thickness. A plurality of recesses  210  is provided on body portion  160  and extends through the entire thickness of sidewall  200 . In another embodiment of bullet  100 , recesses  210  extend only partially through the thickness of sidewall  200 . In such embodiment, recesses  210  may extend from the outside of bullet  100  toward internal cavity  190 , or from internal cavity toward the exterior side of bullet  100 . One or more recesses  210  are disposed circumferentially in the radial direction of body portion  160  and are offset longitudinally along a central axis  220  of bullet  100 . While the recesses  210  illustrated in  FIGS. 3-5  are shown as extending in a direction perpendicular to longitudinal axis  220 , one or more recesses  210  may be angled with respect to longitudinal axis  220 . In another embodiment of bullet  100 , one or more recesses  210  may be disposed circumferentially in the radial direction of body portion  160 , with radially offset patterns in the longitudinal direction of body portion  160 . In some embodiments, one or more recesses  210  may be provided in a randomly distributed arrangement on bullet  100 . 
     With reference to  FIG. 4 , internal cavity  190  of bullet  100  includes a plurality of trusses  230 . Each truss  230  extends in a radial direction across internal cavity  190  of bullet  100 . While  FIG. 4  shows trusses  230  as extending radially inward from an interior portion of the sidewall  200 , in an alternate embodiment, trusses may extend radially outward from an exterior portion of the sidewall  200 . Additionally, each truss  230  may extend across the entire internal cavity  190  or across a portion thereof. Trusses  230  may extend in a direction perpendicular to longitudinal axis  220 , as illustrated in the figures. Alternatively, trusses  230  may extend in a direction that is angled with respect to longitudinal axis  220 . Each truss  230  includes a plurality of spokes  240  extending radially outward from a central portion  250  to interior portion of sidewall  200 . Areas between spokes  240  are hollow to minimize the weight of bullet  100 . Transition portions between individual spokes  240  and central portion  250  or interior portion of sidewall  200  may be rounded.  FIG. 4  illustrates the spokes  240  being connected to interior portion of sidewall  200  between recesses  210  in the radial direction. Alternatively, spokes  240  may be connected to interior portion of sidewall  200  at a location between recesses in the longitudinal direction. In some embodiments, the number of trusses  230  corresponds to the number of rows of recesses  210  in the longitudinal direction of bullet  100 . Optionally, bottom portion of bullet  100  opposite the conical tip  170  may be enclosed. 
     Trusses  230  reinforce the structure of bullet  100  such that it can withstand firing through a barrel of a weapon without being collapsed. Various conventional bullet calibers can be adapted for use with trusses  230  described herein. For example, bullet  100  can be adapted for use with small caliber weapons, such as handguns and light rifles, or large caliber weapons, such as gas or grenade guns or light artillery. Exemplary caliber size may range, without limitation, from .17 to .95. Regardless of caliber size and use in military, hunting, or law enforcement applications, bullet  100  desirably has one or more trusses  230  to reinforce the structure of the bullet body. 
     With reference to  FIG. 6 , another embodiment of bullet  100  is illustrated. In this embodiment, bullet  100  has an identical external structure to the bullet illustrated in  FIGS. 2-5 . However, bullet  100  shown in  FIG. 6  includes an internal ridge  260  extending circumferentially within an internal cavity. Ridge  260  extends radially inward from the interior portion of the sidewall such that a thicker sidewall profile is created at the location of ridge  260 . Ridge  260  is illustrated in  FIG. 6  as being located forward of the plurality of recesses  210  closer to the conical tip of bullet  100 . Alternatively, ridge  260  may be provided between the rows of recesses  210  in the longitudinal direction of bullet  100 , or in any other location within the internal cavity. One or more ridges  260  may be provided inside the internal cavity. For example, bullet  100  may have one or more ridges  260  located in a transition portion between cylindrical body portion  160  and conical tip  170  (distal end), one or more ridges  260  between the rows of recesses  210 , and one or more ridges located at a proximal end of the cylindrical body portion. This embodiment may or may not include the trusses  230  shown in  FIG. 4 . 
     Referring to  FIGS. 7-8 , alternate embodiments of bullet  100  and its corresponding cartridge  110  are shown. In these embodiments, ammunition round  120  is adapted for use with a weapon having a non-rifled barrel, such as a shotgun. With reference to  FIG. 7 , cartridge  110  has a generally cylindrical form including a closed bottom portion  130 , an open top portion  135 , and a cartridge sidewall  140  extending circumferentially therebetween. In this embodiment, cartridge  110  may be constructed from a plastic material. A primer  150  is located at the terminal end of closed bottom portion  130  for interacting with a firing pin of a weapon (not shown). The interior of cartridge  110  is filled with a charge  155  in the form of a powder. Bullet  100  is provided on open top portion  135  such that the cartridge  110  encloses substantially all of bullet  100 . A filler material  190  optionally may be disposed between charge  155  and bullet  100 . Open top portion  130  includes a crimped section  200  to enclose bullet  100  before ammunition round  120  is fired. After firing, bullet  100  forces open the crimped section  200 . 
     With reference to  FIG. 8 , a cartridge  300  for use with a bullet  310  in accordance with another embodiment is illustrated. Cartridge  300  has a generally cylindrical form including a closed bottom portion  320 , an open top portion  330 , and a cartridge sidewall  340  extending circumferentially therebetween. In this embodiment, cartridge  300  may be constructed from a plastic material. A primer  350  is located at the terminal end of closed bottom portion  320  for interacting with a firing pin of a weapon (not shown). The interior of cartridge  300  is filled with a charge  360  in form of a powder. Bullet  310  is provided on open top portion  330  such that the cartridge  300  encloses substantially all of bullet  310 . A gas seal  370  and a spacer  380  are provided between charge  360  and bullet  310 . Gas seal  370  and spacer  380  provide a surface for the expanding gases to push after charge  360  is ignited. A filler material  390  optionally may be disposed between charge  360  and bullet  310 . Open top portion  330  includes a crimped section  400  to enclose bullet  310  before an ammunition round is fired. After firing, bullet  310  forces open the crimped section  400 . 
     Referring to  FIG. 9 , another embodiment of bullet  310  is shown without the corresponding cartridge  300  shown in  FIG. 8 . Bullet  310  has a cylindrical body portion  410  and a conical tip  420  monolithically formed with body portion  410 . Conical tip  420  may have a pointed terminal surface  430 . Alternatively, the conical tip  420  may terminate at a blunt end (not shown). The interior of body portion  410  and conical tip  420  is hollowed out to form an internal cavity  440 . A sidewall  450  defines the structure of body portion  410  and conical tip  420 . Interior cavity  440  may be filled with a truss  470  formed from, for example, a polymeric material to at least partially fill internal cavity  440 . Truss  470  reinforces sidewall  450  from collapsing when bullet  310  is fired. In another embodiment, truss  470  may be made from a metallic material. 
     With continuing reference to  FIG. 9 , body portion  410  includes a recessed portion  460  extending into sidewall  450  of body portion  410 . Recessed portion  460  is slightly undercut compared to an external diameter of body portion  410  to reduce friction of bullet  310  as it travels through the barrel upon firing. A part of body portion  410  that extends past recessed portion  460  forms a driving band  480  that forms a reinforcing truss structure that may contact the gun barrel as bullet  310  travels through the barrel. A leading edge of driving band  480  proximate to conical tip  420  transitions into the radius of conical tip  420 . 
     Bullet  100 ,  310  can be used as a frangible configuration, where limited bullet impact is required. For example, bullet  100 ,  310  may be adapted for use on ships and planes, where the bullet must be capable of impacting a person without piercing the fuselage. In such embodiments, bullet  100  may disintegrate into a plurality of fragments or may flatten upon impact. 
     Having described the construction of the bullet in accordance with one embodiment of the present invention, a method of manufacturing bullet  100 ,  310  will now be described. Bullet  100 ,  310  may be manufactured from a metallic or plastic material of sufficient material strength to withstand being fired through a barrel of a weapon. Various manufacturing techniques may be utilized to manufacture bullet  100 ,  310 . For example, bullet  100 ,  310  may be machined from a solid block of material. In some embodiments, internal cavity  190 ,  440  of bullet  100 ,  310  may be machined, cast, forged, or manufactured in a similar manner, while one or more trusses in bullet  100  may be glued or welded inside internal cavity  190  between recesses  210 . In other embodiments, bullet  100 ,  310  may be manufactured using a 3D printing technique by laying down successive layers of material. For example, bullet  100 ,  310  may be made from bronze or a brass alloy. Other non-limiting examples of materials from which bullet  100 ,  310  may be made include a stainless steel-bronze matrix, a tungsten-copper matrix, a copper bronze-matrix, and iron-copper matrix. For high-powered rounds, it is desirable to construct bullet  100 ,  310  from a material having sufficient hardness to prevent warping due to high firing forces. In certain embodiments, a copperwashed layer may be added to add lubricity for lower friction within the barrel. In embodiments where bullet  100 ,  310  is made from a non-metallic material, an exemplary material exhibiting good lubricity and mechanical strength properties is polytetrafluoroethylene (PTFE), commonly known as TEFLON®. 
     While various embodiments of the hollow bullet were provided in the foregoing description, those skilled in the art may make modifications and alterations to these embodiments without departing from the scope and spirit of the invention. For example, it is to be understood that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment. Accordingly, the foregoing description is intended to be illustrative rather than restrictive. The invention described hereinabove is defined by the appended claims and all changes to the invention that fall within the meaning and the range of equivalency of the claims are to be embraced within their scope.