Patent Document

RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 10/643,831, filed Aug. 19, 2003, which is a non-provisional application claiming the benefit of Provisional Application Ser. No. 60/404,979, filed Aug. 21, 2002, the contents of both being hereby incorporated in their entireties. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to ammunition and in particular to a sabot and slug forming a firearm round wherein a compression section forms a payload receiving area. 
     BACKGROUND 
     A sabot is a commonly used ordnance term to define a sleeve or carrier to center a sub-caliber projectile in a gun bore. Upon firing, the sabot generally separates from the projectile after the assembly leaves the gun muzzle. Sabots may be used with both conical-shaped bullets as well as traditional lead ball bullets. When used with a firearm with a rifled barrel, the sabot may be used to impart rotation to the projectile as it travels down the gun barrel after firing. In particular, the sabot is typically formed to have a diameter the same as the grooved diameter of the rifled barrel so that the sabot is pressed into the rifling after firing. 
     Some of the problems encountered in providing a sabot bullet for shotguns include the fact that there exist large variations in shotgun bore diameters, configurations and interior taper or choke. The shellcase diameter will normally exceed the bore diameter or the choke, and therefore any load component, e.g., projectile, wadding, sabot, etc., must either be of a lesser diameter than the minimum choke diameter, or be formed of a material which may compress or otherwise be capable of deformable flow to pass through the choke. 
     What is needed is a sabot capable of providing safe firearm operation with a low dispersion in an efficient energy transfer manner without damaging the gun barrel. 
     SUMMARY 
     Briefly described, the present invention is generally directed to a sabot for a firearm. The sabot includes a compression section defining a payload receiving chamber. The compression section typically includes a plurality of interconnected collapsible fins that can partially collapse when the firearm round is fired. The payload receiving chamber may include a post and a locking ring fitted within the chamber. Additionally, the sabot includes a solid section connected to the compression section. The solid section can include a powder cup section for trapping ignition gasses. Typically, the sabot is formed from a high density polyethylene or similar high strength synthetic material. 
     Additionally, included in the invention is a firearm round including a sabot and a slug. The sabot includes a compression section defining a payload receiving chamber and a solid section connected to the compression section. The slug is fitted within the payload receiving chamber of the sabot. The slug generally comprises three sections including a stem connected to a driving band and a nose connected to the driving band. The nose section of the slug may include a nose cavity, while the post section includes a post cavity for engaging the post of the payload receiving chamber. The slug commonly comprises at least about 95% by weight lead, though other types of slug material also can be used as known in the art. 
     In an alternative embodiment, the firearm round includes a sabot having a compression section defining a payload receiving chamber therein and a post integrally formed within the payload receiving chamber. A solid section is connected to the compression section and a slug is fitted to the post of the sabot and rests on the compression section of the sabot. 
     Various objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading the following specification when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a firearm round comprising the slug and sabot according to one embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the firearm round of  FIG. 1 ; 
         FIG. 3  illustrates the sabot including the compression section and the solid portion of the sabot; 
         FIG. 4  is a cross-sectional view of the sabot illustrating both the locking ring and the sabot post; 
         FIG. 5  depicts the slug having a nose, driving band and a stem; 
         FIG. 6  is a cross-sectional view of the slug incorporating the nose cavity and post cavity; 
         FIG. 7  is an alternative embodiment of the firearm round wherein the slug rests on the compression section of the sabot; 
         FIG. 8  is a cross-sectional view of the alternative embodiment illustrating the post and hollow slug; and 
         FIG. 9  depicts a firearm round comprising the slug and sabot according to one embodiment of the present invention, wherein the solid section of the sabot is shortened. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now in greater detail to the drawings, in which like numeral indicate like parts throughout the views and drawings.  FIGS. 1 and 2  illustrate one example embodiment of a firearm round  2  comprising a sabot  4  and a slug  6 . The slug  6  is mounted in the payload receiving chamber  8  of the sabot  4 . Typically, the slug  6  has an interference fit with the sabot  4 ; however, the sabot also can, initially, be a loose fit with the slug. Additionally, after the round is fired, the slug typically is further engaged with the sabot  4  by the forces resulting from the sudden acceleration of the firearm round  2 . 
       FIGS. 7 and 8  illustrate an alternative embodiment where the slug is substantially hollow and projects forwardly from the compression section  10  of the sabot  4 . Additionally, a post  16  substantially fills the payload receiving chamber  8 . 
     Sabot 
       FIGS. 3 and 4  the sabot  4  portion of the firearm round  2 . The sabot  4  may be made from linear, high-density polyethylene (HDPE). However, a wide variety of polymers could serve as a suitable material. The sabot generally comprises two sections that can be integrally formed or can be attached as stages or sections. The forward portion or that portion of the firearm round that is the greatest distance from the charge comprises the compression section  10 . The reward section comprises the solid section  12 . The compression section  10  generally includes a plurality of interconnected fins  20  that define or form the accordion shaped compression section  10 . The fins  20  are further collapsible so as to, partially, compact as the round  2  is discharged from the firearm. Additional embodiments are also contemplated for the compression section  10  other than the fins  20  such as, but not limited to, overlapping segmented rims and collapsible wall segments. The solid section  12  may have varying lengths depending upon the embodiment of the sabot  4 . As illustrated in  FIG. 9 , the solid section  12  may be shorter in length than that illustrated in  FIGS. 3 and 4 . 
     The collapse of the compression section  10  produces a volume change to the substantially solid plastic column at the sabot, which allows the internal ballistic characteristics to be modified for optimum performance. The radially symmetric collapse of the compression section  10  walls optimizes the internal ballistics of the loaded round by allowing the forming propellant gases to expand into an increasing volume. For a short duration, this volume expansion allows propellant gases to be expanded while limiting the rise in chamber pressure. The net effect is to allow the projectile to be ejected from the gun at a higher velocity when operating at a maximum peak pressure limit. The area under the pressure-time curve is effectively increased with the peak pressure potentially being held below industry standards for maximum pressure. The compression section  10  is an axisymmetric body of rotation. This allows for substantially uniform, annular compression of the plastic material forming the compression section during the inertial setback of the slug round during firing, which allows the natural centering of the slug post with the sabot and consequently with the bore. Therefore, less projectile deformation is experienced and on-target dispersion is significantly reduced. 
     As shown in  FIG. 4 , a combination of internal and external ridges forms the plurality of interconnected fins  20  which allows the compression section  10  to collapse and, upon firing, the base of the stem  22  of the slug  6  and the bottom of the cavity in the compression section  10  are driven together with sufficient force to reform the slug  6 . The metal of the slug  6  is swaged into the spaces between the ridges inside the sabot  4 . This forms a positive lock between the slug  6  and sabot  4  and ensures consistent longitudinal placement of both the center of gravity and the center of pressure, and to further minimize dispersion of the round. The bottom of the payload receiving chamber  8  also has a post  16 , as shown in  FIG. 4 , which facilitates the expansion of the slug stem  22 . The post  16  is not a requirement, as the stem of the slug will “nail-head” significantly without it. 
     Additionally, a locking ring  19  generally is mounted in the payload receiving chamber  8  and engages the slug  6  received therein. The ring  19  serves to support the slug  6 , and minimize slug distortion. The ring  19  can be made of plastic and minimizes the contact of the metal portion of the projectile with the rifling, thus reducing lead deformation. The ring  19  can also include an undercut to serve as an additional locking feature, although such an additional feature is not required. The inner diameter of ring  19  can have a chamfer or radius to facilitate the insertion of the slug. 
     Furthermore, the sabot  4  includes a propellant powder cup section  14  formed at the rearward section or end of the solid section  12  of the sabot  4  closest to the propellant charge for the round. The cup-shaped propellant or powder cup section  14  is in direct contact with the propellant and seals against the combustion gases generated upon firing. The powder cup section  14  generally is flexible enough to provide a good seal, while possessing the proper rigidity to prevent excessive deformation, which could affect dispersion. 
     The solid section  12  of the sabot  4  primarily functions to set the overall length of the sabot  4 . The length of the solid section  12  can be varied in order to make the sabot suitable for different shell lengths. Typically, the sabot  4  has a length that allows it to be used in both 2¾″ and 3″ shells, although it could also be modified for use in larger or smaller shells as desired. Additionally, the solid section  12  may also include holes or cutouts to reduce the mass of the sabot. Such holes or cutouts may be desirable to improve the ease with which the part is molded. 
     Slug 
     The slug generally is illustrated in  FIGS. 5 and 6 . The slug  6  is received and fitted within the payload receiving chamber  8  of the sabot  4 . Typically, the slug  6  is formed from lead or a lead alloy, and will include a nose  26 , a driving band  24  positioned adjacent the nose  26 , and a stem  22  connected to and extending rearwardly from the driving band  24 . In greater detail, the slug  6  projectile may be composed of about 95% by weight lead or greater and may include antimony or other materials as known in the art. Additionally, the slug could be coated or plated with a number of materials in order to improve the functional or ballistic characteristics of the system. 
     The stem  22  of the slug is a substantially cylindrically shaped section that generally is small enough in diameter to be easily inserted into the receiving chamber of the sabot  6 . The length of the stem  22  may be adjusted such that it projects into the receiving chamber of the compression section sufficiently to ensure that the sabot remains attached. The relationship of the length of the stem  22  and the compression section is such that the compression section is not allowed to compress completely solid and thereby preventing the slug stem from deforming. If the stem is too long, the compression section will not collapse sufficiently, resulting in unfavorable ballistics. If the stem is too short, the compression section will reach a solid, fully compressed state. This condition prevents the slug from being deformed sufficiently to lock the slug and sabot together. The slug and sabot are locked together to avoid separation forces that could cause increased dispersion. The sabot may either be discarded or retained on impact with the target medium. The stem also has a shallow cavity in its base, or a post cavity  28 , which engages the post  16  in the payload receiving chamber  8  to aid in centering the slug  6  in the sabot  4  as it is formed. The length of the stem  22  can also be used to fine-tune the location of the center of gravity for the improvement of dynamic and gyroscopic stability. 
     The driving band  24  is the portion of the slug  6  that can engage the rifling of the barrel of a rifled firearm. The outer diameter of the band  24  typically is at or near the bore or groove diameter of a firearm such as a rifle, shotgun or other type of firearm in which the sabot of the present invention is used. The length of the band is long enough to ensure that the barrel rifling will induce sufficient spin to stabilize the projectile. However, if the band is too long, the depositing of lead in the barrel may adversely affect dispersion of metal from the lead slug  6 . 
     The nose  26  of the slug  6  is designed such that the aerodynamic center of pressure is well forward of the projectile center of gravity to help ensure that the projectile is gyroscopically stable. Furthermore, a nose cavity  30  can be located in the nose  26  of the slug. The nose cavity  30  is a shallow depression in the nose of the slug. The depth of this depression will be optimized to promote expansion without causing the projectile to fragment. This combination can lead to the desirable condition of large expanded diameter (nearly 1″) and high retained-weight (approximately 98%). 
     It will be understood by those skilled in the art that while the present invention has been discussed above with respect to various preferred embodiments and/or features thereof, numerous changes, modification, additions and deletions can be made thereto without departing from the spirit and scope of the invention as set forth in the following claims.

Technology Category: f