Abstract:
A bullet has a jacket and a core seated into the jacket. The core consists of helically formed strands of malleable material swaged into a cylindrical shape. The strands have a uniform pitch along the core, and fragment uniformly into small portions upon impact. A method of making a bullet includes providing helically formed strands of malleable material, swaging the strands, and seating the strands into a jacket.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to firearm ammunition and more particularly to a jacketed bullet that shear fragments on impact and a method of making the bullet.  
         BACKGROUND ART  
         [0002]    It is desirable for a bullet to have good flight performance, including good range and accuracy, and limited penetration ability. The depth of bullet penetration is directly proportional to velocity and size. Bullets that fragment prior to impact or immediately upon impact have limited penetration ability. Such bullets have little or no path of travel after impact, and therefore will not ricochet or pass through the intended target and strike an unintended target. However, bullets that fragment or disintegrate before impact may not be able to achieve desire flight performance.  
           [0003]    U.K. Patent No. 11,087 to Weiss discloses a hollow base bullet with a mantle and a core pressed into the mantle through an open posterior end. The mantle is weakened by grooves in the anterior end. The core is a single solid leaden piece with incisions therein, or several twisted pieces of lead wire. Wiess states that the disclosed bullet will pass through a target and burst on impact with a hard body.  
           [0004]    U.S. Pat. No. 122,620 to Maduell discloses an unjacketed bullet having four interlocking segments. The segments of Maduell would separate upon firing, and prior to impact, from a rifled firearm barrel due to centrifugal force.  
           [0005]    U.S. Pat. No. 3,208,386 to Schneider et al. discloses a bullet having several elongated metal segments with the ends of the segments fitted into a base cup, and the segments are then swaged to form the desired bullet shape. The bullet of Schneider et al. separates upon firing and prior to impact due to centrifugal force to provide a shotgun type pattern.  
           [0006]    U.S. Pat. No. 5,569,874 to Nelson discloses a bullet having a larger central copper wire and several smaller copper wires around the central wire, with the tail ends of the wires swaged into a jacket. After impact the tip ends of the wires separate while the tail ends of the wire are retained in the jacket.  
           [0007]    U.S. Pat. No. 5,528,989 to Briese discloses a bullet having a jacket and a leaden core with the core being formed by swaging a plurality of straight wires into a cylinder. The wires, after swaging, interlock with each wire having end sections that extend parallel to the longitudinal axis of the core. Each wire has a kinked intermediate section that includes two oblique sections, the oblique sections connecting together and each oblique section connecting to an end section.  
           [0008]    U.S. Pat. No. 5,679,920 to Hallis et al. discloses a bullet with a copper jacket and a core of segments of zinc, iron, steel or copper. The core is created by forming a hollow roll or cylinder of twisted wires, and work hardening the wires by high impact swaging to make the wires brittle. The wires in the core after swaging are distorted and have an interlocking pattern similar to the pattern disclosed in U.S. Pat. No. 5,528,989 to Briese, and are not arranged helically. The disclosed bullet fragments upon impact with a hard barrier such as a sheet of metal.  
           [0009]    U.S. Pat. No. 5,582,255 to Hallis et al. discloses a bullet with a copper jacket and a core having wires of zinc, iron, steel or copper. The core includes heart having a plurality of wires extending parallel to the longitudinal axis of the core and a plurality of wires twisted around the heart. The core is high impact swaged to deform the wires and to make the wires brittle. The disclosed bullet fragments upon impact with a hard barrier such as a sheet of metal.  
         DISCLOSURE OF THE INVENTION  
         [0010]    A fully jacketed bullet is disclosed including a metal jacket and a core. The jacket has a base and a cylindrical body extending from the base. The core includes a plurality of strands of malleable material having a low shear modulus. The strands are helically formed or twisted together, and swaged into a uniform cylindrical shape. The core is seated into the jacket and the jacket is then point formed. The method disclosed includes providing a plurality of helically formed strands, swaging the strands to form a uniform cylindrical core, providing a jacket, seating the core in the jacket and point forming the jacket. The strands each have a uniform pitch around the core so that the shock wave that is created by the impact of the bullet and that travels longitudinally rearwardly along the bullet, uniformly and predictably shear fragments and disintegrates the strands. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Details of this invention are described in connection with the accompanying drawings that bear similar reference numerals in which:  
         [0012]    [0012]FIG. 1 is a side view of a bullet embodying features of the present invention.  
         [0013]    [0013]FIG. 2 is a perspective view of the core of the bullet of FIG. 1 prior to swaging.  
         [0014]    [0014]FIG. 3 is a perspective view of the jacket and core of the bullet of FIG. 1 after swaging of the core.  
         [0015]    [0015]FIG. 4 is a top view of the bullet of FIG. 1 prior to point forming.  
         [0016]    [0016]FIG. 5 is sectional view taken through the line  5 - 5  of FIG. 4.  
         [0017]    [0017]FIG. 6A is a side view of a core of a bullet with a plurality of strands parallel to the direction of travel.  
         [0018]    [0018]FIG. 6B is a side view of the fragmentation pattern of the bullet of FIG. 6A upon impact.  
         [0019]    [0019]FIG. 6C is an end view of the damage track of the bullet of FIG. 6A.  
         [0020]    [0020]FIG. 7A is a side view of a core of a bullet with two kinks in a plurality of strands.  
         [0021]    [0021]FIG. 7B is a side view of the fragmentation pattern of the bullet of FIG. 7A upon impact.  
         [0022]    [0022]FIG. 7C is an end view of the damage track of the bullet of FIG. 7A.  
         [0023]    [0023]FIG. 8A is a side view of a strand of a core of a bullet with a smoothly helically formed strands.  
         [0024]    [0024]FIG. 8B is a perspective side view of the fragmentation pattern of a core of a bullet having the strands of FIG. 8A upon impact.  
         [0025]    [0025]FIG. 8C is a side view of the fragmentation pattern of the strand of FIG. 8A upon impact.  
         [0026]    [0026]FIG. 8D is an end view of the damage track of the bullet of FIG. 8A. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Referring now to FIGS.  1  to  5 , a bullet  10  embodying features of the present invention includes a jacket  11  and a core  12 . As shown in FIG. 2 the core consists of a plurality of strands  14 , of a selected length, helically formed together in a spiral configuration so that each strand  14  extends rotationally around a longitudinal axis  15  of the core  12  and obliquely to the axis  15 .  
         [0028]    The strands  14  are made of a malleable metal. Metals having a low shear modulus are preferred. Lead, with a shear modulus of about 0.8 million pounds per square inch (psi) or lead alloy are preferred. Other suitable metals include tin and magnesium, both with a shear modulus of about 2.4 million psi, and aluminum, with a shear modulus of about 3.0 million psi. Less suitable metals include copper and zinc, each with a shear modulus in the range of 6 million psi.  
         [0029]    The helically formed strands  14  of the core  12  are low impact swaged into a uniform cylinder  16  as shown in FIG. 3. The term low impact swaging as used herein refers to swaging metal through high pressure, such as in a low speed hydraulic press, rather than through a sudden, violent impact. Low impact swaging is distinguished from high impact swaging in that high impact swaging uses a sudden, violent impact to form metal. High impact swaging work hardens metal and makes metal brittle. The process of swaging bullets is known in the art, and well described in U.S. Pat. No. 5,528,989, incorporated herein by reference.  
         [0030]    Swaging the helically formed strands  14  of the core  12  provides a dynamically balanced core  12  with no voids for good flight performance. Prior to swaging the helically formed strands  14  of the core  12  have a mass slightly greater than the selected mass of the resultant cylinder so that excess material can be pushed out of bleed holes in the swaging die and the core  12  for each bullet  10  for a specific application will have exactly the selected mass.  
         [0031]    The diameter of the combined helically formed strands  14  of the core  12 , prior to swaging, is slightly less than the diameter of cylinder  16  and the length of the helically formed strands  14  of the core  12  is slightly longer than the cylinder  16 . Swaging compresses the helically formed strands  14  of the core  12  so that the rotations per inch or pitch of the helically formed strands  14  of the core  12  increases.  
         [0032]    The jacket  11  has a base  18  and an elongated, hollow, cylindrical side wall  19  of uniform thickness, attached to and extending transverse the base  18 . The length of wall  19  is greater than the length of core  12 . The base  18  and wall  19  form a cylindrical cavity  20  that is open opposite the base  18 . The jacket shown has a flat base  18 , however other configurations are suitable, such as the rebated boattail. The diameter of the core  12  after swaging is slightly less than the diameter of the cavity  20  so that the core  12  may be readily inserted into cavity  20  and no air will be entrapped between core  12  and base  18  when core  12  is inserted into cavity  20 .  
         [0033]    As shown in FIGS. 4 and 5, the core  12  is seated in the jacket  11  against the base  18  after insertion of core  12  into cavity  20 . The seating of core  12  includes pressing core  12  so that core  12  shortens and deforms outward to solidly contact wall  19 . After the core  12  is seated in jacket  11 , the bullet  10  is point formed such that the jacket  11 , opposite base  18 , has an inwardly tapering tip  21 , as shown in FIG. 1. The core  12  that extends into tip  21  will also be deformed into an inwardly tapering configuration by the point forming.  
         [0034]    [0034]FIG. 6A shows a bullet  30  with eight strands  32  that extend parallel to the direction of bullet travel. At impact the leading edge of bullet  30  is momentarily compressed. This compression induces a pressure wave that travels in the direction directly opposite the flight direction of bullet  30 . Bullet  30  may have a velocity of about 3000 feet per second. The pressure wave travels at the speed of sound. The speed of sound in lead is about 4000 feet per second. Therefore, the pressure wave travels rearwardly the length of bullet  30  before bullet  30  penetrates the length of bullet  30 .  
         [0035]    The pressure wave separates the strands  32  as shown in FIG. 6B. The pattern of the damage track for the bullet  32  shown in FIG. 6A resembles an eight pointed star as shown in FIG. 6C. The separation of bullet  30  into the eight strands  32  significantly reduces the penetration.  
         [0036]    [0036]FIG. 7A shows a bullet  40 , similar to several prior known bullets, with eight strands  42  that extend generally parallel to the direction of bullet travel with each strand  42  having two kinks  43 . The pressure wave created at impact travels parallel to, but in the opposite direction to, the direction of bullet travel. Strands  42 , at the kinks  43 , are not parallel to the direction of bullet travel. When the pressure wave reaches a kink  43 , a shear stress is created in the strand  42 . Strand  42  breaks if the shear stress exceeds the shear fracture limit.  
         [0037]    As shown in FIG. 7B, each strand  42  breaks at kinks  43  into three pieces, creating twenty-four fragments  44  from the eight strands  42 . The damage track for the bullet  40  of FIG. 7A is shown in FIG. 7C and has twenty-four spokes. Since each strand  42  separates into three fragments  44 , the penetration of bullet  40  of FIG. 7A is significantly less than the bullet  30  of FIG. 6A.  
         [0038]    [0038]FIG. 8A shows a smoothly helically formed strand  14  of the bullet  10  embodying features of the present invention. The strand  14  is continually oblique to the pressure wave, so the pressure wave produces shear stresses along the whole length of strand  14  and strand  14  separates at shear fractures  24  into many fragments  23 , as shown in FIGS. 8B and 8C. The fragments  23  are more nearly uniform in size than prior known fragmenting bullets. FIG. 8C shows the damage track of the bullet  10 . The damage track has a diffuse uniform circular pattern. Since each strand  14  of bullet  10  separates into many fragments  23 , the penetration of bullet  10  embodying features of the present invention is significantly less than the bullet  40  of FIG. 7A.  
         [0039]    The shear stresses increase as the angle of strand  14  increases relative to the direction of the pressure wave. The number of fragments  23  increases, and the size of the fragments  23  decreases and therefore the penetration depth decreases, as the pitch or turns per inch of the strands  14  increases. The number of fragments  23  also increases as the number of strands  14  increases. Between one half and five turns are suitable for the bullet  10 , and between two and fifteen strands  14  are suitable for bullet  10 . Since the fragments  23  are more uniform in size than prior known bullets, the penetration and impact pattern of bullet  10  are more predictable.  
         [0040]    Bullet  10  has a full jacket  11  to minimize drag in flight and to assure that core  12  does not disintegrate prior to impact. Jacket  11  has a uniform wall thickness for balance. Similarly, core  12  is swaged into a uniform cylinder  16  for balance and further seated in jacket  11  for balance. Bullet  10  must be well balanced to prevent tumbling and disintegration before impact. Core  12  is preferably swaged into cylinder  16  before seating so that each bullet  10  will have a uniform selected precise mass. Jacket  11  and core  12  do not have incisions or grooves that would unbalance the bullet  10 . Jacket  11  does not have grooves that would weaken the jacket  11  and cause the jacket  11  to burst from the pressure required to seat core  12 .  
         [0041]    The method of making the bullet  10  includes the steps of providing a plurality of strands helically formed together in a spiral configuration, low impact swaging the strands into a cylindrical core with the strands maintaining the spiral configuration, providing a cylindrical jacket with a closed base, seating the core into the jacket, and point forming the jacket opposite the base.  
         [0042]    Although the present invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made by way of example and that changes in details of structure may be made without departing from the spirit thereof.