Patent Publication Number: US-2005126422-A1

Title: Bullet with booster filling and its manufacture

Description:
This application claims the benefit of U.S. Provisional Application No. 60/367,843 filed on Mar. 25, 2002 and U.S. Provisional Application No. 60/432,492 filed on and Dec. 10, 2002; the disclosures of which applications are incorporated by reference as if fully set forth herein. 
    
    
     TECHNICAL FIELD  
      This invention relates to improvements to bullets having an open, forward end cavity, including hollow point bullets. In particular, the invention relates to a filling to be applied to the cavity of a hollow point bullet for the purpose of improving, hastening and assuring its expansion and other purposes and to devices and methods for introducing the filling into the cavity.  
     BACKGROUND ART  
      In this document, these terms are defined as follows: 
          TARGET: The desired place of impact of a bullet.     LIQUID TARGET: A target that behaves like a liquid having a density of 1.0, such as 10 percent gelatin or human soft tissues.     INTERMEDIATE BARRIERS: Materials interposed between the gun and the target that must be perforated if the bullet is to strike the target.        

      For defense purposes, bullet efficiency is measured by the probability that a bullet&#39;s impact will stop an aggressive behaviour and is called “stopping power.” Stopping power is strongly related, to the pressure intensity generated by the bullet when it strikes its target. Pressure wave intensity depends, in turn, on the maximum bullet diameter achieved during expansion and the square of the velocity at the moment of maximum expansion.  
      Because high striking velocities can be attained only with long-barrelled guns, like rifles, efforts have been directed toward improve the efficiency of ammunition fired with portable short-barrelled guns, like pistols and revolvers, that cannot achieve high striking velocities. The practical way to improve the efficiency of these weapons is to employ bullets that increase in diameter during penetration of the target.  
      As illustrated in  FIGS. 1, 2  and  3 , one solution to this problem that is taught in the background art is to employ soft lead bullet  12  (see  FIG. 1 ) or a bullet with soft lead tip  14  and bullet jacket  24  (see  FIGS. 2 and 3 ). Pure lead is quite soft and has yield strength of about 1.6 kilogram per square millimetre (k/mm 2 ). This approach requires a striking velocity above  410  meters per second (m/sec) to expand a lead bullet. As illustrated in  FIG. 4 , a plain lead bullet or one with a soft lead tip expands in a mushroom shape  164 .  
      The body of a human or an animal is heterogeneous but is composed mostly of water and can be considered a liquid target. High velocity bullets fired into liquids like water or living tissue are severely distorted. It is evident that the liquid resistance to penetration, related to the stagnation pressure has a significant effect on the shape of the bullet. Media like gelatin blocks are employed as targets during testing to simulate living tissues.  
      When a bullet penetrates a liquid mass at high velocity, the liquid flows around the bullet nose creating pressures that vary with location and that reach a maximum value in what is called stagnation area. This area is that part of the bullet forward surface that is perpendicular to the direction of movement. The pressure at this point is called the stagnation pressure. As is illustrated in  FIG. 9 , stagnation pressure is related to the square of the bullet&#39;s velocity. Hand gun bullets have velocities ranging from 300 to 450 m/sec, corresponding to stagnant pressures from 500 to 1,000 kg/cm 2 . This phenomenon is responsible for bullet deformation.  
      To increase the amount of bullet deformation, the hollow point bullet has been devised. A number of background art designs for hollow point bullets are illustrated in  FIGS. 5-12 . One approach is to use a drill to produce cavity  20  having an open, forward end in the nose of a conventional (plain) bullet, as illustrated in  FIG. 5 . Cavity shape may vary according to the bullet design. Some hollow point bullets are made with pure lead, as illustrated in  FIGS. 5, 7  and  10 , with cavity  20  having an open, forward end at the nose and closed cavity end  30  at the rear end of the cavity. These bullets require lower velocities than soft point bullets to achieve larger expansions. Most hollow point bullets (see  FIGS. 11 and 12 ) comprise jacket  24  and require ( FIG. 12 ) a higher velocity and slits  74  formed in the nose portion  28  to expand.  
      Pascal&#39;s principle states that, in a liquid at rest in a closed container, a pressure change in one part of the liquid is transmitted without loss to every other part of the liquid and to the walls of the container. A hollow point bullet with an open, forward-end cavity is not a closed container. Only when the hollow point bullet strikes a liquid target at high velocity, does the liquid penetrate with high pressure into the open, forward end of the cavity transmitting the pressure to the walls of the cavity, in accordance with Pascal&#39;s principle.  
       FIG. 16  illustrates the progressive expansion of hollow point bullet  40  as it penetrates liquid target  38 . In this example, the velocity at which bullet  40  strikes target  38  is about 350 m/sec. This is a typical handgun bullet velocity.  
      At initial position  44 , bullet  40 , with its hollow point cavity  20  empty, is about to strike target  38 . Because of the bullet&#39;s high velocity and the inertia of the liquid molecules of target  38 , bullet  40  must travel a certain distance and reach cavity filling completed position  46  before cavity  20  is completely filled with the liquid of target  38 . Only when cavity  20  is filled is the stagnation pressure on the bullet tip transmitted throughout the liquid inside cavity  20  and is applied to the walls of cavity  20 , starting expansion at expansion initiation position  48 .  
      Once cavity  20  is filled at cavity filling complete position  46 , and because of the inertia of the material of which bullet  40  is made, bullet  40  must travel about ten mm more through target  38  to expansion initiation position  48  before the walls of cavity  20  begin to expand radially and the expanded area is simultaneously bent backward by target axial pressure  62 . Expansion of bullet  40  continues at continuing expansion position  50  after a total travel about eighty mm through target  38 . By this position, the forward end of bullet  40  has been transformed into ring  56  with the metal at its outer diameter bent backward. The maximum diameter that occurs seldom reaches seventy percent larger than the original caliber. By this position, the velocity of bullet  40  has been reduced by about twenty percent to about 280 m/sec and the pressure wave intensity, which is related to the stagnation pressure and maximum expanded ring diameter, has reached its maximum value. Passing through maximum expansion position  52 , bullet  40  continues to penetrate target  38 , without further deformation, until its velocity drops to zero.  
      For a given velocity, the larger the expansion achieved by bullet  40 , the lower the penetration achieved by bullet  40 , because these phenomena are antagonistic. For example, for a conventional 9 mm hollow point bullet, the average maximum expansion achieved in testing media is about sixteen mm and the penetration is about 300 mm. If expansion is reduced, for example to twelve mm, stopping power is also reduced but penetration increases to 500 mm.  
      Some police forces require ammunition with a high stopping power (which increases with larger expansion) and deep penetration (which decreases with larger expansion). What is needed is a bullet that fulfils these requirements.  
      Much deeper penetration with larger expansion can be achieved with hollow point bullets by increasing the striking velocity above 400 m/sec. In that penetration in liquids is a logarithmic function of velocity, small increases in velocity (from 350 to 410 m/sec) do not effectively increase penetration. The observed penetration increase is due to other reasons. With velocities above 400 m/sec, the bullet&#39;s expanded area after reaching its maximum diameter is reduced by fractures, leaving a stump which has a diameter close to the original calibre and about eighty percent of the original mass. It is the stump that achieves deeper penetration. Stopping power is related to the maximum pressure wave intensity, even if it only lasts a few microseconds (1/1,000,000 of a second). Thus, it does not matter that, after expanding, the bullet fractures and its expanded area is reduced.  
      This mechanism explains the success (in terms of stopping power) of hollow point 357 calibre magnum bullets. The velocity of these bullets is about 430 m/sec, which insures a large expansion and a subsequent fragmentation of the expanded ring. Velocities as high as this are very difficult to achieve in calibres other than magnums. What is lacking in the background art is an approach that causes the bullet to expand sufficiently to achieve the fracture, combining high stopping power with deep penetration, but at much lower velocities than are possible with magnum calibres.  
      The degree of expansion of hollow point bullet  40  also depends on how completely the liquid of target  38  fills cavity  20 . If cavity  20  is not completely filled, hollow point bullet  40  does not expand.  
      In police applications, very often a bullet must perforate what are called “intermediate barriers” before striking the target. Typical intermediate barriers are car doors or windshields, wood door panels, gypsum construction panels, and leather objects like a belt or heavy clothing such as is worn in winter. Today, this is so important that most handgun ammunition evaluations carried out by police forces measure bullet performance only after the bullet has penetrated an intermediate barrier.  
      If hollow point bullet  40  penetrates an intermediates barrier such as (such as wood, textiles, leather or gypsum) before striking final target  38 , cavity  20  can fill with debris associated with penetrating the intermediate barrier that prevents cavity  20  from being filled with the liquid of target  38 . Under these conditions, the bullet does not expand, defeating the purpose of the hollow point.  
      If hollow point bullet  40  penetrates an intermediates barrier such as a thin plate metal as is encountered in car doors or metallic furniture, the hollow point nose will be riveted, closing the cavity and also defeating the purpose of the hollow point. Intermediates barriers such as wood, textiles, leather or gypsum, are easily perforated by hand gun bullets, as their thickness and resistance are low. However, hollow points are easily filled by the barrier&#39;s material. In these cases, the bullet does not expand and behaves as an undeformable bullet. Stopping power is reduced and penetration in liquid targets or tissue simulants increase to unacceptable values. What is needed is a filling for the hollow point cavity so it cannot be filled by debris so that its performance remain unchanged after perforating barriers such as wood, textiles, leather or gypsum.  
      Metal plates offer a different kind of problem to hollow point bullets. In this regard, metal plates are classified at “thin” or “thick.” A thin metal plate is one that can be perforated by a bullet. A thick plate is one that cannot be perforated. For hand gun ammunition, a thin (mild steel) plate is a No.  20  plate, which is about 0.9 mm thick, or a 2 mm thick hard aluminium alloy.  
      A thick plate is a No.  12  steel plate, which is 2.8 mm thick. This distinction is made because the effect of the bullet on the plate, and the effect of the plate on the bullet, interact continuously during the whole perforation process and are entirely different depending on whether perforation occurs or not.  
      A thick plate impacted by a bullet suffers only elastic deformation, and the bullet is squashed. If the kinetic energy of the bullet is sufficiently high, heat generated by this deformation melts the lead and the bullet disintegrates. If the bullet is jacketed, only the jacket is recovered.  
      Perforation of a thin plate by a high velocity bullet is illustrated in  FIG. 18 . Thin plate  106  is a two mm thick aluminium plate that better shows the side deformation and fracture of bulge  112  than a 0.9 mm steel plate. When plain bullet  108  strikes thin plate barrier  106  at average hand gun velocities (300 to 450 m/sec), plate  106  is stretched, forming initial bulge  112  while the bullet&#39;s tip is riveted, copying the shape of bulge  112 , and increasing the bullet&#39;s diameter. Both deformations are simultaneous. The higher the bullet&#39;s velocity, the smaller the bulge, and the riveted bullet diameter, is. Sides  116  of bulge  112  are stretched becoming thinner at thinner side  114 . When the tension at thinner side  114  exceeds the material&#39;s resistance, circular crack or fracture  120  is produced. Fractured cap  122  has a smaller diameter than the bullet and adheres to the tip of riveted bullet  110 . The diameter of hole  118  is enlarged as the bullet passes through. Hole  118  is clean with a sharp edge and has a larger diameter than fractured cap  122 . As the bulging contains and limits the bullet&#39;s riveting, high velocity bullets expand very little while perforating thin metal plates.  
      The first stages of perforation of thin plate  106  by high velocity hollow point bullet  40  are illustrated in  FIG. 19 . The bullet is riveted like plain bullet to produce hollow point bullet with riveted nose  124 . Cavity  20  disappears. As hollow point bullet  40  is lighter but has the same volume as plain bullet  108 , the length of hollow point bullet with riveted nose  124  is slightly shorter. Because a hollow point bullet has a softer nose than a bullet with a full metal jacket, the riveted diameter is about ten percent larger and the capacity to perforate a thin metal plate is reduced. With the same kinetic energy, a  9 mm full metal jacket bullet can perforate six plates expanding its diameter progressively as successive plates are perforated and reaching a maximum diameter of twelve mm. A conventional Silver Tip® hollow point bullet expands from twelve mm after perforating the first plate to fourteen mm after the last, doubling its average frontal surface area and perforating only three plates.  
      Perforation of steel thin plate  106  by a low velocity plain bullet  108  is illustrated in  FIG. 21 . When striking velocities are low, e.g., around  250  m/sec, large diameter bulge  132  is produced, which is shallow but the deformed area is of plate  106  is several times the diameter of deformed bullet  131 , forming a shallow cone. As the shallow bulge does not restrain the riveting of the bullet, deformed bullet  131  is riveted to a larger diameter than is the case when velocities are high. Perforation is less efficient as more energy is spent to deform deformed bullet  131  and plate  106 . As the depth of large diameter bulge  132  increases, radial cracks  134  are produced at the tip of the bulge. Deformed bullet  131  passes through the cracks, pushing aside the metal to produce irregular perforation  136  (which is called petalling).  
      For training purposes, there is a need for non-expanding bullets that have the same external ballistic features and that insure the same point of impact as currently-employed expanding hollow point bullets. Because a particular hollow point bullet can be designed to have different features (such as the degree of bullet expansion, bullet velocity, target penetration), and because the external appearance of different cartridges (i.e., the bullet assembled into the case) can be indistinguishable, there is a need to provide users with a way to easily differentiate among different cartridges.  
      The background art is characterized by U.S. Pat. Nos. 219,840; 3,348,486; 3,357,357; 3,911,820; 4,338,862; 4,550,662; 4,947,755; 5,208,424; 5,365,853; 5,454,325; 5,763,819; 5,943,749; 6,115,894; 6,115,894; 6,176,186; 6,178,890; 6,305,290; 6,305,292; the disclosures of which patents are incorporated by reference as if fully set forth herein. A description of the limitations of the background art is presented below.  
      As illustrated in  FIGS. 5 and 10 , the first hollow point bullets were made of lead, were unjacketed and were provided with cavity  20  having an open forward end at the tip. U.S. Pat. No. 219,840 issued in 1879 to Winchester does not disclose a hollow point bullet per se, but it does disclose a device for manufacturing hollow point lead bullets similar to the example shown in  FIG. 10 .  
      From 1882 to 1898, British colonial forces employed a .455 calibre revolver that fired lead bullets having a hemispherical hollow point cavity  22 , as illustrated in  FIG. 7 . These bullets were called “Man Stoppers.” In spite of their very low velocity of about 180 m/sec, the bullets expanded by sixty percent (see  FIG. 8 ) after striking a liquid target.  
       FIGS. 10 through 12  illustrate several common handgun hollow point bullets that can be improved in accordance with the techniques disclosed herein.  FIG. 10  presents a conventional, full-lead hollow-point bullet without a case. To prevent barrel fouling with lead, bullets of this type may be either copper clad or coated with Nylon® or Teflon®.  
       FIGS. 11 and 12  show conventional jacketed hollow point bullets. Jacket  24  is made thinner in nose region  28 , and slits  74  are formed at the bullet&#39;s nose to allow jacket  24  to shred during expansion of the bullet according to U.S. Pat. No. 4,193,348 that was issued to Halverston in 1978. This successful design is market by Olin under the trademark Silver Tip®. In this design, cavity  20  is relatively small and jacket  24  is thinner in nose region  28 . Axial slits  74  are formed in jacket  24  at the bullet&#39;s nose. As illustrated in U.S. Pat. No. 5,208,224, jacket  24  lines cavity  20 .  
       FIG. 14  shows a background art design that is disclosed in U.S. Pat. No. 5,943,749. In this design, jacket  24  forms cavity  4 . In several U.S. patents, including U.S. Pat. Nos. 4,550,662; 4,947,755 and 5,763,819; the cavity is tapered to a conical shape.  
      U.S. Pat. No. 3,881,421 that was issued to Burczynski disclosed to a very successful ammunition marketed under the trademark Hydrashock®). The cavity includes a conical central post. Hydrashock® bullets are produced with and without jackets and have a very high expansion ratio. The effects of the central post on expansion and accuracy were evaluated by the FBI in 1990, comparing the effects of identical bullets with and without the central post. The conclusion was that the central post slightly improved the bullet&#39;s performance (WWW domain firearmstactical.com.briefs26htm).  
       FIG. 13  shows a bullet design called Rhino-Ammo, which is not patented but is disclosed in the background art section of U.S. Pat. No. 5,763,819 (col. 5, lines 1-12) and U.S. Pat. No. 6,115,894 (col. 5, lines 21-35). The bullet is not a hollow point type but comprises fully hollowed soft lead bullet  12  filled with a very hard and brittle polymer  70  that fragments into sharp pieces upon impact. According to the bullet manufacturer, the polymer employed is a blend of polyaniline, a high molecular-weight polymer, and carbon-based filaments called “cyanate whiskers.” This reference teaches away from the invention disclosed herein.  
      All the former designs are hollow point bullets that expand while penetrating liquid targets but none comply with the following requirements: preventing the hollow point of a bullet from clogging with debris from intermediate targets; increasing expansion during the perforation of hard materials; preventing the expansion of training bullets during the penetration of liquid targets; and allowing users to identify different cartridge designs that would otherwise have an identical external appearance.  
      U.S. Pat. Nos. 6,178,890 and 6,305,292, which patents were both issued to Burczinzky, propose a solution to the problem of the cavity in a bullet being filled with debris. In these designs, the bullet is jacketed at the bullet&#39;s closed forward end and open at its rear end. This jacket construction is similar to the conventional full metal jacket as specified by NATO, shown in  FIG. 14 . The jacket is closed at the bullet&#39;s nose  28  but open at the rear to allow the introduction of a lead core. The lead core is retained by crimped portion  80 .  
      In the Burczinsky invention, the lead core does not completely fill the jacket, leaving an empty space in the nose that is filled with a polymer. The bullet nose is also provided with axial slits that weaken the jacket&#39;s nose and permit expansion. When the bullet strikes a barrier or the target, the nose is compressed axially, thereby expanding the jacket at the nose. Debris produced after intermediate barriers have been perforated have no effect on bullet expansion as there is no open cavity at forward end of the bullet to be clogged. In that these designs have a jacketed (closed) forward end and  28  open rear end  64 , they cannot be confused with designs that comprise an open forward end or a hollow point.  
      The Burczinsky invention promotes bullet expansion during the penetration of a wide variety of target types. It also prevents the bullet from clogging with debris from intermediate targets because bullets of the Burczinsky design do not have a front open cavity. Notwith-standing these characteristics, it cannot be employed to produce a non-expanding hollow point bullet for training purposes nor does it allow for identification of different cartridge types.  
      Background art bullet manufacturing machines perform necessary bullet-fabrication unit operations in a continuous sequence. The production rate for conventional industrial machines is from one to two bullets per second. What is needed is a device for filling the cavity of a hollow point bullet with an elastomer or a rigid polymer that can be integrated into conventional production machines and achieve commercial production rates.  
      None of the references and no combination of the references teach techniques that can be used to cause a bullet to produce a large frontal area that fractures after having expanded during the penetration of a liquid target, combining high stopping power with deep penetration, but at much lower velocities than are possible with magnum calibres. None of the references and no combination of the references teaches techniques that can be employed to prevent training hollow point bullets from expanding during the penetration of a liquid target. None of the references and no combination of the references teaches techniques that can be employed to increase the expansion of hollow point bullets during the penetrating of hard targets. Moreover, none of the references and no combination of the references teach how to effectively manufacture an elastomer-filled hollow point bullet or a rigid polymer-filled hollow point bullet.  
     DISCLOSURE OF INVENTION  
      The embodiments of the invention disclosed herein achieve one or more of the following purposes: improving, hastening and assuring bullet expansion during the penetration of liquid targets; preventing the hollow point of a bullet from clogging with debris from intermediate targets; increasing bullet expansion during the perforation of hard materials; preventing the expansion of training bullets during the penetration of liquid targets; and allowing users to identify different cartridge designs that would otherwise have an identical external appearance. Another purpose is to provide a technique for designing bullets that achieve these ends.  
      In one aspect, the invention comprises filling the cavity of a hollow point bullet having an open forward end with a solid substance that transmits pressure throughout its mass as if it were a liquid. Filling of the cavity with such a substance hastens the expansion process and prevents the cavity from filling with debris.  
      Preferably, the filling is an elastomer that transmits the pressure (e.g., stagnation pressure) applied to the open forward end of the cavity in the bullet (e.g., when the bullet strikes a liquid target or a simulated tissue) to the interior surface of the cavity. The invention is advantageous because it can be employed in all existing hollow point bullets, regardless of the cavity shape, whether the bullet is jacketed or not. Hollow point bullets fitted with the filling of the invention disclosed herein are unaffected by the penetration of intermediate barriers that would otherwise fill the hollow point cavity with debris, thus impeding the bullet&#39;s expansion. Moreover, thin metal plate penetration can be reduced by combining the approach of filling the cavity with an appropriate elastomer with modification of other ammunition features, such as bullet shape and velocity. The invention provides much better performance than similar ammunition, in terms of cost, stopping power, penetration depth and metal plate perforation performance.  
      In a preferred embodiment, the invention is a bullet comprising: a bullet body having a cavity in its forward end that is open at that end and an elastomer filling situated within said cavity. Preferably, the elastomer filling comprises a two-component silicon elastomer. In a preferred embodiment, the elastomer filling has Shore hardness in the range from about 6 to about 90. Preferably, the elastomer filling is vulcanized. More preferably, the vulcanized elastomer filling has a Shore hardness in the range from about 6 to about 90. More preferably, the vulcanized elastomer filling has a Shore A harness of about 70. Preferably, the elastomer is colored, i.e., the elastomer is not clear, but rather a color such as red, green or yellow, etc.  
      In a preferred embodiment, the bottom of the cavity is rounded or non-planar. In another preferred embodiment the bottom of the cavity is square or flat. In yet another preferred embodiment, the cavity has axial grooves. In a further embodiment, the elastomer filling is a plug having axial grooves or axial holes.  
      In a preferred embodiment, the elastomer filling is formed into a cylindrical insert before it is inserted in the cavity. Preferably, the insert is exposed to lubricant that can be absorbed by the filling after it is forced into the cavity. Preferably, the elastomer filling is a vulcanizible elastomer that is poured into the cavity before it is vulcanized. In a preferred embodiment, the elastomer filling comprises a thermoplastic that is injected into the cavity. In a preferred embodiment, the elastomer filling is operative to transmit stagnation pressure to the walls of the cavity when the bullet strikes a liquid target. In another preferred embodiment, the elastomer filling is operative to flatten and convert axial forces into radial forces that contribute to bullet expansion when the bullet strikes a hard target.  
      In another preferred embodiment, the invention is a bullet body having a cavity in its forward end that is open at that end and an elastomer filling situated within said cavity, wherein the characteristics of the bullet are indicated by the color of the elastomer filling, said color being visible at the nose of the bullet.  
      In another preferred embodiment, the invention is a training bullet comprising: a bullet body having a cavity in its forward end that is open at that end and a rigid polymer filling situated within said cavity, wherein said filling is operative to cause the bullet to have the same ballistic features as a bullet having an elastomer filling of approximately the same size and is operative to prevent the bullet from expanding during penetration of a liquid target. Preferably, the rigid polymer filling is colored. In a further embodiment, the rigid polymer filling is a plug having axial grooves or axial holes. Preferably, the rigid polymer filling has the same density as the elastomer filling that is used in the non-training version of the bullet.  
      In another preferred embodiment, the invention is a bullet body having a cavity in its forward nose end that is open at that end and a plug compressed within said cavity by swaging or crimping said nose. Preferably, the plug has a loose fit in the cavity prior to being compressed in the cavity by swaging or crimping.  
      In another preferred embodiment, the invention is a cartridge comprising: a cartridge case containing the bullet disclosed herein, a powder charge or load and a primer.  
      In another preferred embodiment, the invention is a bullet having an unjacketed, flat nose comprising: a metal body having a hollow point that is filled with an elastomer.  
      In another preferred embodiment, the invention is a bullet comprising: a generally cylindrical, metal body portion having a longitudinal axis and a first axial cavity portion disposed along the longitudinal axis; a metal nose portion disposed forwardly of said body portion, said nose portion having an unjacketed forward end and a second axial cavity portion disposed along the longitudinal axis; and a generally cylindrical elastomer filling situated within the axial cavity portions, said elastomer filling having a generally flat or slightly convex forward end.  
      In another preferred embodiment, the invention is a bullet comprising: a metal body having a generally cylindrical portion and a frontal portion having a first longitudinal cavity part; and an elastomer portion, at least a first part of which is disposed in the first cavity part, the elastomer portion having a generally flat, unjacketed forward end. In some embodiments, the cylindrical portion and the frontal portion are also unjacketed. In some embodiments, the generally cylindrical portion has a second longitudinal cavity part in which a second part of the elastomer portion is also disposed. In some embodiments, the tip of the frontal portion has a smaller diameter than the diameter of the cylindrical portion.  
      In another preferred embodiment, the invention is an adequate penetration, optimum expansion bullet for use against barriers of soft to medium-hardness comprising: a jacket formed of a malleable metal and having a generally cylindrical sidewall, a nose portion disposed forwardly of said cylindrical sidewall, an open forward end, and a rear end portion; said nose portion having a nose-defining wall extending between said cylindrical wall and said open forward end; an elastomer core disposed in part at least within said nose-defining wall; and a metal core seated behind said elastomer core and within said generally cylindrical sidewall in close-fitting relation and extending rearwardly to a position adjacent said rear end portion of said generally cylindrical jacket sidewall.  
      In another preferred embodiment, the invention is a projectile comprising: a metal body having a generally cylindrical portion and a frontal portion, both the cylindrical portion and the frontal portion having a longitudinal cavity having walls; and an elastomer portion that is disposed in the cavity, the elastomer portion having a generally flat, unjacketed forward end and being operative to transmit a stagnation pressure that is exerted upon the forward end when the projectile strikes a barriers to the walls of the cavity.  
      In another preferred embodiment, the invention is a bullet comprising: a metal body having an open cavity in its forward end, the cavity having walls, and means for transmitting a stagnation pressure that is exerted upon the forward end when the bullet strikes liquid barriers to the walls of the cavity.  
      In another preferred embodiment, the invention is a process for making an improved bullet comprising: filling a cavity in a bullet having a flat front end with an elastomer plug, the plug having a flat forward end that ends in the approximately same plane as the front end. Preferably, the filling step involves placing a thermoplastic elastomer plug into a hollow point bullet.  
      In another preferred embodiment, the invention is a process for making an improved bullet comprising: filling a cavity in a bullet having a nose with a plug and then swaging or crimping the nose. Preferably, the plug has a loose fit with the cavity prior to the swaging or crimping step.  
      In a further preferred embodiment, the invention is an apparatus and a process for producing the bullets disclosed herein. Preferably, the apparatus for inserting an elastomer into a cavity in a bullet comprises: a table for supporting a bullet; a rotary plate having a plurality of holes along its periphery that are operative to accept a segment of cord, said plate being rotatably connected to the table and being capable of shearing off said segment of cord during its rotation; and an elastomer cord feeding device having a cord feeding device bushing that situated adjacent to the rotary plate and through which the cord feeding device is capable of feeding cord into each hole in the rotary table; and a punch having a punch bushing that situated adjacent to the rotary plate and through which the punch is operative to push the sheared segment of cord into the cavity in the bullet.  
      In another preferred embodiment, the invention is another apparatus for inserting an elastomer into a cavity in a bullet comprising: a table for supporting a bullet; a reciprocating feeder having a hole in one end that is operative to accept a segment of cord, said feeder being slidably connected to the table and being capable of shearing off said segment of cord during its backward movement; and an elastomer cord feeding device having a cord feeding device bushing that situated adjacent to the reciprocating feeder and through which the cord feeding device is capable of feeding cord into the hole in the reciprocating feeder and pushing the sheared segment of cord into the cavity in the bullet when the feeder is in the forward position.  
      Further aspects of the invention will become apparent from consideration of the drawings and the ensuing description of preferred embodiments of the invention. A person skilled in the art will realize that other embodiments of the invention are possible and that the details of the invention can be modified in a number of respects, all without departing from the concept. Thus, the following drawings and description are to be regarded as illustrative in nature and not restrictive. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The features of the invention will be better understood by reference to the accompanying drawings which illustrate presently preferred embodiments of the invention. In the drawings:  
       FIG. 1  is an elevation view of a handgun bullet.  
       FIG. 2  is an elevation view of a soft tip bullet.  
       FIG. 3  is a cross-sectional view of a soft tip bullet.  
       FIG. 4  is an elevation view of an expanded soft tip bullet.  
       FIG. 5  is a cross-sectional view of a conventional hollow point bullet.  
       FIG. 6  is a cross-sectional view of an expanded conventional hollow point bullet.  
       FIG. 7  is a cross-sectional view of an alternative hollow point bullet.  
       FIG. 8  is a cross-sectional view of an expanded alternative hollow point bullet.  
       FIG. 9  is a plot of stagnation pressure versus bullet velocity.  
       FIG. 10  is a cross-sectional view of a conventional full lead hollow point bullet.  
       FIG. 11  is a cross-sectional view of a conventional jacketed hollow point bullet.  
       FIG. 12  is an elevation view of a jacketed hollow point bullet showing nose slits.  
       FIG. 13  shows a cross-sectional view of a bullet employed in Rhino-Ammo™.  
       FIG. 14  is a cross-sectional view of a conventional full metal case bullet.  
       FIG. 15  is a cross-sectional view of a preferred embodiment of the invention.  
       FIG. 16  is a time-lapse illustration of a conventional hollow point bullet penetrating a liquid target.  
       FIG. 17  is a time-lapse illustration of a hollow point bullet that has been improved in accordance with a preferred embodiment of the present invention penetrating a liquid target.  
       FIG. 18  is a time-lapse illustration of the first stages of a high velocity, hollow point, hand gun bullet penetrating a thin metal plate.  
       FIG. 19  is a time-lapse illustration of a high velocity conventional hand gun bullet penetrating a thin metal plate.  
       FIG. 20  is a time-lapse illustration of the first stages of a high velocity, hollow point, elastomer-filled, hand gun bullet penetrating a thin metal plate.  
       FIG. 21  is a time-lapse illustration of a low velocity, conventional hand gun bullet penetrating a thin metal plate.  
       FIG. 22  is a time-lapse illustration of a low velocity, elastomer-filled, hollow point hand gun bullet penetrating a thin metal plate.  
       FIG. 23  is a cross-sectional view of a bullet and a filling plug with air bleeding grooves in accordance with a preferred embodiment of the invention.  
       FIG. 24  is a cross-sectional view of the bullet of  FIG. 23  with the filling plug inserted.  
       FIGS. 25A and 25B  are cross-sectional views of a bullet with a plain filling plug and bleeding grooves in the cavity wall in accordance with a preferred embodiment of the invention.  
       FIGS. 26A and 26B  are cross-sectional views of a jacketed bullet prepared to receive an elastomer plug in accordance with a preferred embodiment of the invention.  
       FIGS. 27A and 27B  are cross-sectional views of a jacketed bullet showing a stress raiser and a plug ready to be inserted in accordance with a preferred embodiment of the invention.  
       FIGS. 28A and 28B  are cross-sectional views of a jacketed bullet with a stress raiser and the plug inserted in accordance with a preferred embodiment of the invention.  
       FIGS. 29A and 29B  are cross-sectional views of the bullet of  FIG. 28  after the nose has been swaged.  
       FIG. 30  is a cross-sectional view of a jacketed bullet with an annular stress raiser in accordance with a preferred embodiment of the invention.  
       FIG. 31  is a cross-sectional view of a jacketed bullet with the stress raiser forming tool inserted in the cavity raiser in accordance with a preferred embodiment of the invention.  
       FIGS. 32A and 32B  are cross sectional views of a stress raiser forming tool in accordance with a preferred embodiment of the invention.  
       FIG. 33  is a cross sectional view of a counter-tapered cavity being filled with a polymerizing elastomer in accordance with a preferred embodiment of the invention.  
       FIG. 34  is a cross-sectional view of a cartridge of a preferred embodiment of the invention disclosing the position of the center of gravity and the dimensions of the powder load chamber.  
       FIG. 35  is a cross-sectional view of the cartridge of  FIG. 34  with a plain bullet.  
       FIG. 36  is a cross-sectional view of the cartridge of  FIG. 34  with a lighter bullet.  
       FIG. 37  is a cross-sectional view of the cartridge of  FIG. 34  with a bullet having a concave base.  
       FIG. 38  is a cross-sectional view of the cartridge of  FIG. 34  with a cavity filled with a rigid polymer in accordance with a preferred embodiment of the invention.  
       FIG. 39  is a cross-sectional view of a preferred embodiment of the invention with a very heavy bullet relative to the bullet of  FIG. 40 .  
       FIG. 40  is a cross-sectional view of a preferred embodiment of the invention with a lighter bullet relative to the bullet of  FIG. 39 .  
       FIG. 41  is an elevation view of a plug feeding machine having a rotary plug holder in accordance with a preferred embodiment of the invention.  
       FIG. 42  is a cross-sectional view of a plug feeding machine showing a plug ready to be punched into a cavity in a bullet in accordance with a preferred embodiment of the invention.  
       FIG. 43  is a cross-sectional view a plug feeding machine with a plug inserted into a cavity in the bullet in accordance with a preferred embodiment of the invention.  
       FIG. 44  is a plan view of a reciprocating plug feeding machine with a reciprocating plug holder in the rear (back) position in accordance with a preferred embodiment of the invention.  
       FIG. 45  is a plan view of a reciprocating plug feeding machine with a reciprocating plug holder in the forward position in accordance with a preferred embodiment of the invention.  
       FIG. 46  is a plan view of a reciprocating plug feeding machine with a reciprocating plug holder in the forward position in accordance with a preferred embodiment of the invention.  
       FIG. 47  is a cross-sectional view a reciprocating plug feeding machine with a plug sheared by the holder in accordance with a preferred embodiment of the invention.  
       FIG. 48  is a cross-sectional view a reciprocating plug feeding machine showing the sheared plug ready to be inserted into the bullet cavity in accordance with a preferred embodiment of the invention.  
       FIG. 49  is a cross-sectional view a reciprocating plug feeding machine showing the sheared plug pushed in the bullet&#39;s cavity by the cord in accordance with a preferred embodiment of the invention. 
    
    
      The following reference numerals are used to indicate the parts and environment of the invention on the drawings: 
           12  soft lead bullet, lead core, bullet body      14  soft lead tip      18  grooved cavity, cavity with axial grooves      20  cavity, empty cavity      22  hemispherical hollow point cavity, cavity with round bottom      24  bullet jacket, partial jacket, stamped jacket, jacket      28  nose portion, nose region, nose, forward end      30  closed cavity end, cavity bottom, bottom      38  target, final target, liquid target      40  hollow point bullet      41  improved hollow point bullet, bullet with plug inserted      42  elastomer filling, filling, compressed elastomer filling      44  initial position, position prior to entry      46  cavity filling completed position, cavity filled position      48  expansion initiation position      50  continuing expansion position      52  maximum expansion position      54  fragmentation position      56  expanded ring, ring      58  fragments      60  stump      62  axial pressure      64  open rear end      70  brittle polymer      74  slits, axial slits      75  axial grooves      80  crimped portion      88  plain cylindrical plug, cylindrical plug, plug      90  plug with axial grooves      94  polymerizing elastomer      96  copper cladding      97  case, casing      100  powder filling space, standard powder load      102  smaller powder space, reduced powder load      106  thin plate, plate      108  plain bullet      110  riveted bullet      112  bulge      114  thinner side      118  hole      120  fracture      122  fractured cap      124  hollow point bullet with riveted nose      126  riveted elastomer-filled nose      130  sheared plug      131  deformed bullet      132  large diameter bulge      134  radial cracks      136  irregular perforation      138  table      139  holes      140  rotary plate, rotating plug holder, plate      142  feeding device bushing      144  punch busing, bushing      146  punch      150  extruded cord, cord      152  cord feeding device      154  reciprocating feeder, feeder      158  first prototype bullet      160  second prototype bullet      162  center of gravity      164  mushroom shape      166  stress raisers, axial stress raisers      168  annular stress raiser      170  stress raiser forming tool      172  expanding mandrel      173  annular lip      174  conical end      176  radial cuts        

     MODES FOR CARRYING OUT THE INVENTION  
      Referring to  FIG. 15 , a preferred embodiment of the invention is illustrated. In this embodiment, the bullet comprises bullet body  12  having cavity  20  in the nose  28  that is open at the cavity&#39;s forward end, filling  88  situated within cavity  20  and partial jacket  24 . Preferably, filling  88  is either a colored synthetic elastomer compound with a Shore hardness of about 70 or a colored rigid polymer filling (such as an ethylene copolymer), depending on whether an expanding or a non-expanding hollow point bullet is desired.  
      Referring to  FIG. 17 , the progressive expansion of improved hollow point bullet  41  with elastomer filling  42  in cavity  20  is illustrated in initial position  44  just prior to penetrate liquid target  38  at a velocity of about 350 m/sec. Because hollow point cavity  20  is already filled at initial position  44 , the stagnation pressure is applied to elastomer filling  42  as soon as it strikes target  38 .  
      After traveling about ten mm, expansion starts at expansion initiation position  48 . After traveling about ten mm more, the expansion of improved hollow point bullet  41  reaches a maximum value at maximum expansion position  52 , after a total travel in liquid target  38  of about 40 mm. Axial pressure  62  simultaneously expands bullet  41  and bends ring  56  backwards.  
      At maximum expansion position  52 , the velocity of improved hollow point bullet  41  is reduced to about 300 m/sec. This velocity is about 30 m/sec higher than it would have been had improved hollow point bullet  41  had an empty cavity as was the case for conventional hollow point bullet  40  in  FIG. 16 . Because stopping power is related to the maximum pressure wave intensity that in turn is related to the square of the bullet&#39;s velocity, the stopping power of improved hollow point bullet  41  is increased significantly over that of conventional hollow point bullet  40 .  
      With a striking velocity of 350 m/sec it is very difficult to disintegrate the expanded ring of a conventional hollow point bullet. Because the improvements disclosed herein also act as an expansion booster, it is possible to increase the ring&#39;s diameter until it disintegrates at fragmentation position  54  to produce fragments  58 . At fragmentation position  54 , stump  60  remains, with a diameter close to the original caliber and with a velocity close to the 300 m/sec attained at maximum expansion position  52 .  
      As penetration in liquid targets is inversely related to bullet diameter and directly related to the bullet mass, at fragmentation position  54 , the bullet has lost about 20 percent of its original mass but its diameter has been reduced by 50 percent. This is why the smaller diameter stump  60  achieves a much deeper penetration into target  38  than if the expanded bullet did not fragment. As illustrated in  FIG. 30 , if the fracture of expanded ring  56  is sought and bullet&#39;s velocity is insufficient to cause fragmentation to occur, fracture can be induced by forming an annular stress raiser  168  at the cavity&#39;s bottom.  
      Comparing the bullet&#39;s effect on a testing media, it is noticeable that with the elastomer filled hollow point bullet of the disclosed invention, expansion begins immediately after striking an intermediate barrier and the transitory cavity produced is larger. If expanded ring  56  disintegrates, stump  60  retains about eighty percent of the original bullet&#39;s weight and has a much deeper penetration into the target than a similar but conventional unfilled hollow point bullet.  
      Moreover, if the elastomer filled bullet of the disclosed invention strikes an intermediate barrier, debris does not fill the cavity. If, after striking intermediate barriers, it strikes a liquid target, expansion begins immediately and is more regular than if the cavity were empty.  
      The disclosed invention can be used to improve all hollow point bullet designs, including those described U.S. Pat. Nos. 219,840; 3,348,486; 3,357,357; 3,911,820; 4,338,862; 4,550,662; 4,947,755; 5,208,224; 5,365,853; 5,454,325; 5,763,819; 5,943,749; 6,115,894; 6,176,186; and 6,178,890; the disclosures of which patents are incorporated by reference as if fully set forth herein. In all cases, the bullet becomes immune to the effect of striking intermediate barriers. Furthermore, expansion begins sooner, increasing pressure wave intensity.  
      Depending on the original design of the bullet being improved in accordance with the invention disclosed herein, expansion may also be increased. This is not always the case: for example, when a Silver Tip® bullet made in accordance with U.S Pat. No. 4,193,348, is improved in accordance with the invention disclosed herein, the bullet becomes unaffected by intermediate barriers but other performance criteria, such as maximum pressure wave intensity and thin plate perforation, remain unchanged. Furthermore, when the invention disclosed herein is applied in a completely new bullet design, a more efficient bullet can be produced.  
      While a hollow point bullet cavity having an open forward end is not a closed container, Pascal&#39;s principle can be applied when the bullet strikes a liquid target because, at high velocity, all of the liquid inside the cavity is submitted to the stagnation pressure that is applied through the open forward end of the bullet and is consequently transmitted to the walls of the cavity.  
      The larger expansion and particularly the higher pressure wave generated by elastomer filled hollow point bullets during the penetration of liquid targets is explained by the bullet&#39;s higher velocity at the moment full expansion is reached. The effects of the elastomer being placed in the hollow point cavity are different when the bullet strikes hard targets (such as thin metal plates or glass). While an empty hollow point has no effect on bullet expansion when the bullet strikes a thin metal plate, the presence of an elastomer filling has a strong positive effect.  
      Perforation of thin plate  106  by a high velocity hollow point elastomer filled bullet is illustrated in  FIG. 20 . Riveting forces flatten elastomer filling  42  to produce riveted elastomer-filled nose  126  and convert the axial forces into radial ones that contribute to bullet expansion. In spite of the riveting, filling  42  is retained and the hollow point is not closed. The riveted diameter is about ten percent larger than an unfilled hollow point and twenty percent larger than a plain (solid) bullet.  
      Different materials have different effects when used for filling an open forward-end cavity in a bullet. Solids, either crystallized or powdered, transmit the pressure in the same direction as it is applied (e.g., axially, in the case of a bullet) without affecting the walls of the cavity. Consequently, solids such as rigid polymers are preferably employed if a hollow point bullet is not intended to expand during the penetration of liquid targets, as it is the case with training ammunition. If expansion is sought, liquids cannot be employed as a filling, because they are not retained in the open forward-end cavity. High viscosity thixotropic liquids are retained in the cavity but they cause two problems: (1) such liquids gather dirt at the exposed open forward end and (2) expansion is erratic because thixotropic liquids are sometime dispersed at impact. Waxes and soft malleable solids with a Shore hardness below  30  behave like elastomers but only within a limited temperature range: (1) if the temperature is too high, such solids become liquids and flow out of the open forward-end cavity and (2) if the temperature is too low they crystallize or harden and behave like solids.  
      Elastomers are the preferred solid and stable materials that transmit the pressure according to Pascal&#39;s principle, but these materials have two restrictions. First, the glass transition temperature (the temperature at which the elastomer begins to behave like a solid) must preferably be below the temperatures encountered in cold climates. For example, fluoroelastomers are preferably not employed because they have a glass transition temperature of about −10° C. Second, the hardness selected for the elastomer is preferably related to the stagnation pressure (see  FIG. 9 ) expected to be encountered in use. If a relatively hard elastomer provides a good expansion at about 1,500 kg/mm 2 , it may be too hard and behave as a solid if the stagnation pressure is only about 500 kg/mm 2 . For most handgun ammunition, which experience stagnation pressures around 750 kg/mm 2  (corresponding to velocities from 250 to 400 m/sec), Shore hardness values from six to eighty are preferred. In experiments conducted by the inventor with handgun ammunition improved as disclosed herein, the best experimental results were achieved with an elastomer having a Shore hardness of about seventy.  
      Because hollow point bullets of the same caliber that have different weight, velocity and expansion features and that would otherwise be externally identical can be produced with the techniques disclosed herein, a purpose of this invention is to provide easy identification of different bullet types. This is preferably achieved be employing colored material as the fillings for the hollow point bullets disclosed herein. Many synthetic elastomers and rigid polymers are easily colored. When employed as the filling, they form a visible colored spot, which is easily identified, at the nose of the bullet. If molded plugs are employed, the bullet identification or the manufacturer&#39;s logo can be engraved the plug&#39;s tip.  
      Bleeding means are preferably provided to allow the air trapped below the plug to escape during the insertion process. This is particularly important if plugs are inserted at high velocity (e.g., two plugs per second), because the plug insertion time is about 0.10 sec. For this purpose,  FIGS. 23 and 24  illustrate plug with axial grooves  90  that can be used to allow for bleeding.  
      There are several preferred ways to provide air bleeding during plug insertion to produce preferred embodiments of improved bullet  41 , which improved bullet  41  offers several advantages over a bullet with a cylindrical cavity and a sliding fit plug. One preferred approach is illustrated in  FIGS. 23 and 24 . With this approach, longitudinal (axial) grooves are provided on the plug to produce plug with axial grooves  90 . The grooves can be formed on extruded cord  150 . In another approach (not illustrated), one or more longitudinal holes are formed in the extruded cord. Because it is difficult to produce very small diameter holes in an extruded cord, producing grooves is preferred. Another approach is illustrated in  FIG. 25 . With this approach, a plain (ungrooved) cylindrical plug  88  is employed and groves  75  are formed in the cavity&#39;s wall to produce cavity with axial grooves  18 . These approaches are better suited to rigid poymer plugs that are preferably retained by forming crimped portion  80  at the cavity&#39;s edge as illustrated in  FIG. 24 .  
      Providing plug with axial grooves  90  is a preferred solution as the grooves can be formed in the extruded cord employed with the filling machines disclosed herein. An alternative solution (not illustrated) is to provide an axial hole in the plug. Another alternative, illustrated in  FIG. 25 , is to provide grooved cavity  18  having axial grooves  75 . In this case, a plain cylindrical plug  88  (i.e., one with no grooves) may be employed. If grooves are used for air bleeding, the plug preferably has a sliding fit in the hole. It can be easily retained by crimping the edge of the cavity. This is not a preferred approach for elastomer plugs as crimping reduces bullet expansion. Instead, it is a preferred way to produce a non-expanding hollow point bullet having a rigid polymer filling.  
      A more preferred approach which is better suited to elastomer plugs is illustrated in  FIGS. 26A  and B through  29 A and B. Preferably, with this approach, a large clearance is left between plain plug  88  and the sidewall of cavity  20 . With the appropriate clearance, satisfactory air bleeding can be achieved. When bullet nose  28  is swaged, shown in  FIG. 29  as a subsequent operation, cylindrical plug  88  is compressed and completely fills cavity  20  regardless of the shape of cavity  20  or whether grooves have been formed on the walls of cavity.  
      In this embodiment, cylindrical plug  88  has a smaller diameter than cavity  20  to allow for air to escape through the annual space between the outer walls of plug  88  and the inner walls of cavity  20 . The required volume of plug  88  is that necessary to fill cavity  20  when the full nose has been swaged as in  FIGS. 29A  and B. In this embodiment, it is possible to employ a cavity with a rounded bottom that helps prevent the expanded bullet from breaking up when full expansion has been reached.  
      As illustrated in  FIG. 33 , if the shape of cavity  84  is other than cylindrical, cavity  84  is preferably filled with polymerising elastomer  94  which is deposited in cavity  84  in the liquid state and then polymerized. While the approach of filling a cavity in a bullet with a polymerizing elastomer (as indicated in  FIG. 33 ) is technically feasible, it is not preferred because it is not a convenient approach and because polymerizing elastomers can be expensive. With this approach, the elastomer is applied with an automatic dosing machine. Such machines can be complicated to maintain. In addition, a curing oven must be introduced into the production line to cure the elastomer.  
      An alternative approach, injecting a thermoplastic elastomer into a bullet cavity, is also not preferred because it is a relatively slow and expensive process. With this approach, the bullet must be placed into an injection mold and the associated unit processes (e.g., from feeding the mold to injecting the elastomer) are relatively slow. Use of an injection molding machine is, therefore, a relatively expensive approach, particularly considering the slow output of such machines when filling bullets.  
      In the background art bullets illustrated in  FIGS. 11 and 12 , stamped jacket  24  resists expansion, even though it is thinner at the nose; Slits  74  can be formed prior to the core insertion to allow the jacket to shred upon the bullet&#39;s expansion. If the bullet is copper clad, as shown in  FIGS. 26A  and B, copper cladding  96  has a uniform thickness and slits can not be made prior to insertion of lead core  12 . Axial stress raisers  166 , shown in  FIGS. 27A  and B must be cut through the bullet nose to allow and control expansion. Once plug  88  is inserted, as illustrated in  FIGS. 28A  and B, nose  20  is swaged as shown in  FIGS. 29A  and B. Swaging compresses plug  88  to form elastomer filling  42  and closes the gap in stress raisers  166 . Axial stress raiser technology is disclosed in U.S. Pat. No. 219,840 issued to Winchester, the disclosure of which patent is incorporated by reference as if fully set forth herein.  
      If fracture of expanded ring  56  is sought but bullet velocity is insufficient, fracture can be induced as illustrated in  FIG. 30 , forming annular stress raiser  168  at the bottom of cavity  20 . For this purpose, annular stress raiser forming tool  170 , illustrated in  FIG. 31 , is preferably introduced into cavity  20 . As shown in  FIGS. 32A  and B, stress raiser forming tool  170  is formed by expanding mandrel  172  having annular lip  173 . A shaft with conical end  174  is pulled upon, opening the mandrel and forming internal annular stress raiser  168 . Radial cuts  176  allow the mandrel to open.  
      When a shooter is preparing to employ specialized ammunition such as the elastomer-filled hollow point bullets disclosed herein, he usually trains with a simpler and less expensive version called training ammunition. Training ammunition must have the same recoil and trajectory as the specialized ammunition. The powder loads must be identical and must leave the same empty space bellow the bullet. The bullet also must have the same dimensions, weight and position of its center of gravity.  
      For training purposes, there is a need for non-expanding bullet ammunition that duplicates the recoil and the external ballistic features of a particular hollow point bullet, assuring the same point of impact as that particular hollow point bullet. Recoil is related to bullet weight and powder load and is easily duplicated from one cartridge to another. External ballistics is related to bullet shape and the location of its center of gravity that cannot be duplicated with full non-hollow point bullets.  
      The problem of constructing non-expanding training bullets is illustrated in  FIGS. 34 through 38 .  FIG. 34  illustrates a hollow point bullet with a hollow point cavity that is filled with elastomer filling  42 . Center of gravity  162  is slightly below cavity bottom  30 .  FIG. 35  illustrates the bullet of  FIG. 34  with the cavity removed: the weight of the bullet is higher and center of gravity  162  is moved toward the bullet&#39;s tip.  FIG. 36  illustrates the bullet of  FIG. 34 , shortened to achieve the same weight as the bullet of  FIG. 34 . Center of gravity  162  is displaced forward and powder filling space  100  in case  97  is enlarged, modifying the powder combustion rate.  FIG. 37  illustrates a bullet with a hollow base to maintain its exterior dimensions and weight unchanged. Center of gravity  162  is moved forward and powder filling space  100  in case  97  is enlarged. A preferred solution to achieving unchanged ballistic performance for a non-expanding training bullet when a bullet filling is used is to replace elastomer filling  42  with rigid polymer filling  70  having the same density as the elastomer filling, as illustrated in  FIG. 38 .  
      In a preferred embodiment illustrated in  FIG. 29 , an elastomer-filled hollow point bullet is produced by compressing elastomer plug  42  within the cavity by swaging the bullet&#39;s nose. This is not possible when a rigid polymer plug is used as the filling. Instead, a preferred solution is that illustrated in  FIGS. 24 and 25 A and B, in which, instead of an elastomer plug, a rigid polymer plug is employed. Polymer plug  90  can be formed with the plug filling machines disclosed herein by employing an extruded polymer cord as a starting material. As illustrated in  FIG. 24 , its installation requires formation of crimped portion  80  of the nose of the bullet to hold it in position. Because hollow point bullets with different cavity fillings or having different weights, velocities look alike, the cavity filling is preferably colored to allow for easy differentiation.  
      As illustrated in  FIGS. 26A  and B through  29 A and B, if plug  88  has a sliding fit with larger cylindrical cavity  20 , it must be retained in position by swaging or compressing the bullet&#39;s nose forward end. The forward end of cavity  20  remains open after the swaging step.  
      The bullet-cavity filling approaches illustrated in FIGS.  23  to  29 A and B are very economical, if instead of employing a (relatively expensive) pre-molded elastomer plug, the plugs are cut from an elastomer cord. Thus, a preferred approach is to provide a device that not only cuts the cord (forming the plugs) but also places each plug in the cavity of a bullet.  
      Two preferred devices for performing this task are illustrated herein. A person having ordinary skill in the art of bullet production would understand how to incorporate the devices disclosed herein into a bullet production machine and would understand that other approaches are possible.  
      A first preferred device employs a rotary feeder and is illustrated in  FIGS. 41-43 . The device is preferably comprised of indexed rotary plate or plug holder  140  that turns over fixed table  138 . Rotary plate  140  contains numerous holes  139 , each with a depth equal to the elastomer plug length. At the left, cord feeding device  152  pushes exactly the length of elastomer cord  150  necessary to form a plug through feeding device bushing  142  and into one of the holes  139 . When rotary plate  140  turns, cord  150  is sheared between rotary plate  140  and feeding device bushing  142 , forming sheared plug  88  that is retained in one of the holes  139 . As plate  140  rotates, each plug is conveyed to a position that is in line with the axis of punch  146  and punch bushing  144 . Along the same axis, the centerline of empty cavity  20  in a bullet is indexed below sheared plug  88 . Downward movement of punch  146  through punch bushing  144  forces sheared plug  88  into empty cavity  20 , filling the cavity  20  and producing bullet with plug inserted  41 . Bullets move along table  138  in direction A as illustrated in  FIG. 41 .  
      Rotating plug holder  140  stops at each of the holes  139  to allow, at one side, feeding of cord  150  by cord-feeding device  152 , and, at the opposite side, driving of sheared plug  88  into empty cavity  20  by punch  146 . When punch  146  returns to his initial (up) position, plate  140  turns one increment. The feeding cycle requires accelerating and stopping of plate  140  at a preferred rate of about 0.5 sec per cycle.  
      A second preferred device employs a reciprocating feeder (or shuttle) as illustrated in  FIGS. 44-49 . The device is comprised of reciprocating feeder  154  that slides over table  138 . Reciprocating feeder  154  has a single hole and a preferred sliding movement of about 5 mm for a 3.5 mm diameter plug. Cord feeding device  152  pushes exactly the length of cord  150  necessary to form a plug through bushing  144  into feeder  154 . Sheared plug  130  that was formed during a previous, backward movement of reciprocating feeder  154  (see  FIG. 47 ) is situated above (see  FIG. 47 ) empty cavity  20 . Cord feeding device  152  (see  FIG. 49 ) pushes sheared plug  130  into cavity  20 . In this way, the plug  88  is inserted in the bullet.  
      With the reciprocating feeder approach, sheared plug  130  preferably has a sliding fit in the cavity in the bullet. To retain inserted plug  88 , a second operation is performed in a different machine to produce a light crimping in the top of the bullet cavity, as is illustrated in  FIG. 29 . The advantage of the reciprocating feeder approach is that inertial forces are lower than with the rotary feeder approach, allowing a faster operation.  
      Forming plug  130  from extruded cord  150  and fitting it simultaneously in a hollow point bullet with the machine illustrated in  FIGS. 41 through 49  is a simple, inexpensive and rapid procedure. However, fitting a plug into a cavity with which it has a diametrical interference or even a sliding fit is difficult because air trapped below the plug can make plug introduction difficult. Consequently, air bleeding must be provided. Moreover, the rotary feeder illustrated in  FIGS. 41 through 43  uses punch  146  to drive sheared plug  130 , but with the reciprocating feeder illustrated in  FIGS. 44 through 49 , the force that drives the plug into the cavity is limited, as it must be exerted by cord  150 . For this reason, with the reciprocating feeder, plug  130  must have a sliding fit in cavity  20 . As plug  130  is inserted at a very high velocity, in about 0.17 sec., ample air bleeding must be provided.  
      The shape of the bottom of cavity  20  influences the disintegration of expanded ring  56 . For some applications, an expanded ring that expands and then disintegrates is a sought-after feature. If the bottom of cavity  20  is flat, as shown in  FIG. 23 , the sharp edge at the intersection of the flat cavity bottom and cavity wall concentrates stresses during expansion, promoting the fracture and disintegration of expanded ring  56 . If the sharp edge at the bottom of the cavity is removed by making the bottom rounded of hemispherical as shown in  FIG. 34 , disintegration of expanded ring  56  may be avoided.  
      A more preferred embodiment of the invention has a number of characteristics. Preferably, it comprises a loose-fitting cylindrical elastomer plug that is formed and fitted by a reciprocating machine disclosed herein into a hollow point bullet having a cylindrical cavity and an unfinished nose shape, wherein a finished bullet is achieved by swaging the former bullet to compress the plug inside the cavity.  
      New bullets can be designed so as to embody the invention disclosed herein. Expansion can be adjusted to achieve the required performance through adjustment of cavity dimensions and the placement and design of stress raisers. Even with low velocities, it is possible to design bullets that fracture after expansion. It is also possible to design bullets that expand but do not fracture, retaining most of the original weight.  
     WORKING EXAMPLES  
      Two prototype ammunition designs were developed and tested to illustrate the possibilities of basing a new bullet design on the invention disclosed herein.  
      One is low penetration ammunition. For home defense, ammunition that is issued to personnel with little training in defense or that is employed in crowded areas should be convenient to use and have the following features: good stopping power, i.e., stopping power equivalent to a military (e.g., NATO) ammunition would be the minimum acceptable; low penetration of intermediate barriers, i.e., although police require high penetration of cars in defensive applications, not only would this feature be unnecessary but it may be a handicap in crowded areas or in home defense applications; and low report, i.e., a loud report like that of a 9 mm NATO round may produce permanent hearing damage, while a report that is three decibels (dB) less would make the report acceptable.  
      The second is ammunition for police application that must comply with the “INS National Firearm Unit Ballistic Gelatin Test Protocol.” The bullet must comply with several stringent requirements, such as insensibility to intermediate barriers, high stopping power and satisfactory penetration.  
     Working Example No. 1  
      Thin metal plate penetration increases with the square power of velocity and decreases with the bullet&#39;s frontal surface area. If the only desired feature of a bullet is a low thin metal plate penetration, bullet velocity can be reduced as necessary by reducing the powder load. Automatic pistol ammunition must produce sufficient recoil to operate the slide. Recoil is a linear function of bullet mass and velocity. The maximum bullet mass is limited by the cartridge design. Bullets have a maximum possible length (and mass) limited by the cartridge dimensions, as the assembly cannot exceed a certain length. Comparing  FIG. 39  with  FIG. 40 , it is noticeable in  FIG. 39  that the bullet is longer (and heavier) and consequently smaller powder space  102  left in the case bellow the bullet is restricted. A ten percent increment in the bullet&#39;s mass would reduce the powder capacity by 50 percent, reducing the kinetic energy by the same amount, and the bullet would not have sufficient impulse to operate an automatic pistol. A balance must be reached between the bullet weight, the powder space and the bullet velocity.  
      First prototype 9 mm bullet  158  was comprised of a plain lead alloy and had a weight of 11.7 grams. Because no jacket was provided, embodiments of first prototype bullet  158  were either copper clad or Teflon® coated. The hollow point had a cavity that was 3.75 in diameter by 9.5 mm in length before nose swaging and contained compressed elastomer filling  42  in accordance with the invention disclosed herein.  
      In this example, the bullet had a velocity about 230 m/sec. At this velocity, neither a plain bullet nor a hollow point one expanded while penetrating a thin metal plate or a liquid target. Either bullet, plain or hollow point, penetrated two 0.9 mm steel plates. Calculated stopping power was about 45 percent (too low) and penetration in a liquid target, about 1,200 mm (too much).  
      Employing a hollow point with a cavity filled with elastomer  42 , bullet  158  expanded to fourteen mm after perforating the first plate and denting the second plate. Fired on a liquid target (or testing media), bullet  158  expanded to sixteen mm and penetrated 350 mm. Stopping power was about 65 percent, equivalent to a military bullet. The reduced powder load produced report 3 Db less than military NATO ammunition.  
       FIG. 22  illustrates the deformation of a thin plate by low velocity elastomer filled hollow point bullet  158 . The original hollow point elastomer  42  filling was compressed into lenticular shape within the riveted nose increasing the diameter by 30 percent. As thin plate perforation is an exponential function of the bullet diameter, this increment is sufficient to reduce penetration by half. A heavy (11.7 grams), hollow point 9 mm bullet travelling at 235 m/sec expanded to 13 mm after perforating two consecutive 0.9 mm mild steel plates. The same bullet with the hollow point filled with an elastomer expanded to 17 mm perforating only one plate. Thus, the technique disclosed herein employed with lead low velocity bullets reduced perforation capacity by 50 percent.  
      A low thin metal plate perforation capacity is a sought-after feature if the ammunition is to be fired in places where excessive thin plate perforation capacity may be a liability. Such places include air plane cabins, homes, banks, nuclear or electrical plants control rooms. Low penetration ammunition is preferably expressly designed for such a purpose and hollow point elastomer filled cavities contribute greatly to the achievement of the required performance  
     Working Example No. 2  
      Referring to  FIG. 40 , another cartridge as a preferred embodiment of the invention is illustrated. In this embodiment, the cartridge comprised powder filling space  100  and second prototype bullet  160  having cavity filled with elastomer  42 , both of which were situated in case  97 . Second prototype bullet  160  was comprised of a plain lead alloy with six percent antimony and had a weight of 7.5 grams. Because no jacket was provided, embodiments of second prototype bullet  160  were either copper clad or Teflon® coated. The hollow point had a cavity that was 3.75 in diameter by 9.5 mm in length and contained elastomer filling  42  in accordance with the invention disclosed herein.  
      Upon striking a liquid target at a velocity of 350 m/sec, bullet  160  expanded to sixteen mm, compared to a 12 mm expansion for a Silver Tip® bullet, producing a pressure wave intensity that was 40 percent higher. In that the expanded ring disintegrated after reaching maximum expansion, penetration of second prototype bullet  160  was 440 mm, compared to 200 mm for a Silver Tip® bullet.  
      Second prototype bullet  160  expanded to 14 mm (or 56 percent) after perforating three No. 20 steel plates. The same bullet without an elastomer filling expanded to 12 mm (or 33 percent), perforating four plates. An unmodified Silver Tip® bullet perforated three such plates.  
      Compared with all 9 mm ammunitions on the market, the performance of second prototype bullet  160  was vastly superior in the following ways: lower cost (all other ammunitions are jacketed); insensitivity to intermediate barriers; higher stopping power; deeper target penetration; and similar thin plate perforation.  
      Industrial Applicability  
      The invention disclosed herein has utility in a variety of applications, including those disclosed herein, and in facilitating the design of more efficient, new hollow point bullets. The invention is capable of improving, hastening and assuring the expansion of bullets during the penetration of liquid targets, preventing the bullet from clogging with debris from intermediate targets, increasing bullet expansion during the perforation of hard materials and identifying with a colored spot or an engraved plug tip different cartridges that would otherwise have an identical external appearance. For training purposes, the invention can be used to prevent hollow point bullets from expanding.  
      Many variations of the invention will occur to those skilled in the art. Some variations include modification of existing bullets and cartridges. Other variations call for new bullet and cartridge designs. All such variations are intended to be within the scope and spirit of the invention.