Patent Publication Number: US-6901866-B2

Title: Combustible cased telescoped ammunition assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
   This non-provisional patent application claims priority to provisional U.S. patent application Ser. No. 60/333,577, entitled COMBUSTIBLE CASED TELESCOPED AMMUNITION ROUND ASSEMBLY, filed Nov. 27, 2001, hereby incorporated in its entirety by reference thereto. 

   TECHNICAL FIELD 
   The present invention is related to ammunition rounds, and more particularly to cased telescoped ammunition rounds and ammunition firing systems. 
   BACKGROUND 
   Conventional cased telescoped ammunition is well known, particularly in connection with larger caliber firing systems. Representative conventional cased telescoped ammunition is disclosed in U.S. Pat. No. 4,907,510 (Martwick et al.), U.S. Pat. No. 4,604,954 (Clarke et al.), U.S. Pat. No. 4,335,657 (Bains), U.S. Pat. No. 4,220,089 (Smith); U.S. Pat. No. 4,197,801 (LaFever et al.), U.S. Pat. No. 2,996,988 (Kunz), and U.S. Pat. No. 2,866,412 (Meyer et al.). The cased telescoped ammunition disclosed in these references have drawbacks, and there is a need for a cased telescoped ammunition round assembly that provides improved performance and reliability. 
   SUMMARY 
   The present invention provides an apparatus and method relating to a cased telescoped ammunition assembly that overcomes drawbacks experienced in the prior art. Under one aspect of the invention, a cased telescoped ammunition assembly is configured to be fired from a firing device. The assembly includes a combustible case body and noncombustible end caps connected to opposing ends of the case body. The case body is configured to be substantially consumed in combustion when the ammunition assembly is fired. An internal support structure is positioned in the interior portion of the case body and connected to the end caps. The internal support structure and the end caps define a load-bearing unit that provides a load path substantially independent of the case body. The load-bearing unit is configured to react external loads, such that the combustible case body is substantially isolated from and does not react the external loads. 
   Under another aspect of the invention, a method is provided for firing a cased telescoped ammunition assembly. The method includes loading the cased telescoped ammunition assembly into a breech of the firing device, whereby the ammunition round may be exposed to external loads. The external loads are reacted by the load-bearing unit along the load path, such that the case body is substantially isolated from the external loads. Propellant in the ammunition assembly is ignited, whereby the propellant and the case body are consumed in combustion, and the projectile is propelled into the barrel of the firing device. The end caps and the internal support are noncombustible and define a single spent unit after the propellant and the case body are consumed, and the spent unit is ejected from the breech after the projectile has been propelled into the barrel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a combustible cased telescoped ammunition assembly in accordance with one embodiment of the invention. 
       FIG. 2  is a partially cut-away side elevation view of the ammunition assembly of FIG.  1 . 
       FIG. 3  is an enlarged cross-sectional view taken substantially along line  3 — 3  of  FIG. 1  showing the internal components of the ammunition assembly. 
       FIG. 4  is an enlarged detail view taken substantially at Detail  4  of FIG.  3 . 
       FIG. 5  is a cross-sectional view of the ammunition assembly of  FIG. 1  positioned in a firing device. 
   

   DETAILED DESCRIPTION 
   A combustible cased telescoped ammunition assembly and a corresponding method for firing the ammunition assembly in accordance with one or more embodiments of the present invention are described in detail herein. The following description sets forth numerous specific details, such as specific materials usable for the assembly and specific structures for use in manufacturing the assembly, to provide a thorough and enabling description for embodiments of the invention. One skilled in the relevant art, however, will recognize that the invention can be practiced without one or more of the specific details. In other instances, well-known structures or operations are not shown, or are not described in detail to avoid obscuring aspects of the invention. 
     FIG. 1  is an isometric view of a combustible cased telescoped ammunition assembly  10  in accordance with one embodiment of the invention.  FIGS. 2  is a partially cut-away side elevation view of the ammunition assembly  10 .  FIGS. 1 and 2  show for illustrative purposes the ammunition assembly  10  having a combustible case body  12  supported by top and bottom end caps  14  and  16 . The top and bottom end caps  14  and  16  are noncombustible members rigidly connected to a noncombustible internal support structure  18  ( FIG. 2 ) located within the interior area  19  of the case body  12 . A projectile  20  is contained within the case body  12  and the top end cap  14 . The projectile  20  is configured to be fired out of a conventional firing device (not shown). The use of the combustible case body  12  with the noncombustible end caps  14  and  16  and the noncombustible internal support structure  18  is configured to yield a robust assembly in its pre-fired state. The end caps  14  and  16  and the support structure  18  form a unitary, noncombustible, load-bearing unit that, in the post-fired state, allows for the reliable ejection of the spent item from the firing device. 
   In the illustrated embodiment, the combustible case body  12  is a substantially cylindrical body having an outer diameter slightly smaller than the inner diameter of the breech of the firing device. The case body  12  is fabricated from a combustible composite material, such as a resinated molded fiber composite with an energetic component in the form of nitrocellulose fibers. Alternate embodiments can use other combustible composite materials. The combustible case body  12  is comprised of a forward part  22  and an aft part  24  that mate to form the completed combustible case body  12 . The two-piece case body  12  allows for easier manufacture of the ammunition assembly  10 . Alternate embodiments, however, can use a single-piece case body  12 . 
   As best seen in  FIG. 3 , the case body  12  has top and bottom end portions  26  and  28  that are stepped radially inwardly. Each of the top and bottom end caps  14  and  16  has a cup-shaped configuration with an open mouth portion  30  sized to receive the case body&#39;s respective top or bottom end portion  26  and  28  in a male/female interconnection. Accordingly, the top end portion  26  of the case body  12  fits into open mouth portion  30  of the top end cap  14 , and the bottom end portion  28  of the case body fits into the open mouth portion of the bottom end cap  16 . The case body  12  of the illustrated embodiment engages the top and bottom end caps  14  and  16  in a friction fit that can allow for some axial movement of the case body relative to the end caps, although other configurations can be used in alternate embodiments. 
   The top and bottom end caps  14  and  16  each have an elastomeric sealing ring  32  attached to the open mouth portion  30  and that extends over the top and bottom end portions  26  and  28  of the case body  12 . The sealing rings  32  have an outer diameter approximately the same size as the main portion of the case body  12  and the top and bottom end caps  14  and  16 , such that the ammunition assembly  10  has a fairly uniform outer diameter along its length. The sealing rings  32 , however, are adapted to expand radially outwardly and seal against the forward and aft ends of the breech when the ammunition assembly  10  is fired. The sealing rings  32  are made of an elastomer that can withstand the temperatures and pressures that occur in the firing chamber upon firing the ammunition assembly  10 . After the ammunition assembly  10  has been fired, the sealing rings  32  contract and return substantially to their original pre-fired diameter, so the spent unit can be ejected from the breech of the firing device. 
   The ammunition assembly  10  includes a propellant bed  34  (shown only partially) contained in the case body  12 . The bottom end cap  16  forms the closed bottom end of the ammunition assembly  10  so as to contain the propellant bed  34 . The bottom end cap  16  is a noncombustible member than can withstand the high temperatures and pressures generated upon firing without being consumed. In the illustrated embodiment, the bottom end cap  16  is a steel alloy, although other materials can be used. The bottom end cap  16  removably retains an ignition device  36  (e.g., a primer) that extends into the propellant bed  34  to initiate burning and combustion of the propellant bed  34 . The burning propellant bed  34  generates high pressure gas within the ammunition assembly  10  and the firing chamber of the firing device, thereby propelling the projectile into and through the barrel of the firing device. When the projectile  20  is fired, the outer end face  42  of the bottom end cap  16  seals against the breech face when the ammunition assembly  10  is in the firing chamber to help contain the high pressure gas in the firing chamber. 
   On the opposite end of the ammunition assembly  10 , the top end cap  14  has an enlarged aperture  38  with substantially the same diameter as a leading portion  40  of the projectile  20  to allow for passage of the projectile through the top end cap upon firing. The outer end face  44  of the top end cap  14  is configured to sealably mate with the barrel face of the firing device when the ammunition assembly  10  is in the firing chamber and fired, thereby properly containing and directing the propellant gases through the top end cap into the barrel during the act of firing. The top end cap  14  is also a noncombustible member similar to the bottom end cap  16  that can withstand the temperatures and pressures generated upon firing without being consumed. 
   The top and bottom end caps  14  and  16  are securely interconnected to each other by the noncombustible internal support structure  18  positioned within the interior area  19  of the case body  12 . The case body  12  extends around the support structure  18  but is not rigidly attached to the support structure. The case body  12  is also not rigidly attached to the top and bottom end caps  14  and  16 . In the illustrated embodiment, the case body  12  is sized so it can move a slight distance axially relative to the top and bottom end caps  14  and  16  and the support structure  18  if an external axial load is exerted directly on the case body  12 . Accordingly, the case body  12  essentially “floats” on the support structure  18  between the top and bottom end caps  14  and  16 . 
   The top and bottom end caps  14  and  16  along with the support structure  18  define a load-bearing unit that provides a load path through the ammunition assembly  10 . The load-bearing unit reacts external tensile, compression or bending loads that may be exerted on the ammunition assembly during handling and loading. The load-bearing unit is also configured to have ductile compressive and tensile properties suitable to withstand the pre-firing loads on the ammunition assembly  10 , and also to withstand the forces generated within the firing chamber when the ammunition assembly is fired. The load-bearing unit is substantially independent of the case body  12 , so the case body is substantially isolated from the load path and does not react the external loads. Accordingly, the case body  12  can be made of a combustible material that may not be strong enough to react the external loads without being damaged. 
   The support structure  18  also forms an internal frame-like structure that provides lateral support to the combustible case body  12  so as to help the case body react direct lateral impact loads that may occur during pre-firing handling of the ammunition assembly  10 . The support structure  18  also helps maintain the ammunition assembly&#39;s overall cartridge cylindrical runout, also known in the industry as cylindricity, which is very important when trying to insert the ammunition assembly  10  into a firing chamber without binding interference. 
   In the illustrated embodiment, the support structure  18  includes a cylindrical guide sleeve  50  rigidly affixed to the top end cap  14 . In one embodiment, the guide sleeve  50  has external threads that threadably mate with internal threads formed in the top end cap  14 . The guide sleeve  50  is axially aligned with the top end cap  14  and has an inner diameter substantially identical to the aperture  38  in the top end cap. The guide sleeve  50  snugly yet removably retains the projectile  20  in the interior area  19  and in axial alignment with the case body  12  and the top end cap  14 . The guide sleeve  50  is configured to assist in guiding the projectile  20  into the barrel of the firing device upon firing. In the illustrated embodiment, the guide sleeve  50  is made of a high-strength, noncombustible material, such as a steel alloy or the like, that is able to withstand the high temperatures and pressures created upon firing of the ammunition assembly  10 . 
   The support structure  18  of the illustrated embodiment also has a plurality of elongated support rods  52  securely connected to the guide sleeve  50  and to the bottom end cap  16 . The support structure  18  shown in  FIG. 3  has four elongated support rods  52  equally spaced around the interior area  19  of the case body  12 , although a different number of support rods or other support members could be used. The support rods  52  are substantially rigid and are made of a selected steel alloy, although other materials can be used in alternate embodiments. In the illustrated embodiment, the support rods  52  are shaped as tensile coupons (also known as “dog-bone” coupons) having an elongated middle portion  53  with an outer diameter smaller than the outer diameter at the ends of the support rods. The forward end  54  of each support rod  52  is fixedly retained in a blind hole  56  formed in the aft end  58  of the guide sleeve  50 . The aft end  60  of each support rod  52  is securely connected to the bottom end cap  16 . In alternate embodiments, the aft end  60  of each support rod can be attached to an intermediary mounting structure that fixedly attaches to the bottom end cap  16 . 
     FIG. 4  is an enlarged detail view of a portion of the bottom end cap  16  and an aft end  60  of a representative one of the support rods  52 . The aft end  60  of each support rod  52  extends through an aperture  62  in the bottom end cap  16 . The aft end  60  of each support rod  52  in the illustrated embodiment has an annular shoulder  61  that abuts an annular ridge  63  formed in the aperture  62 . The annular ridge  63  blocks the support rod  52  from axial movement through the aperture  62  in the bottom end cap  16  in response to a compressive load. The aft end  60  of each support rod  52  also threadably attaches to a nut  64  or other suitable fastener securely connected to the bottom end cap  16 . An O-ring  65  is positioned between the nut  64  and the annular ridge  63  to form a seal around the aft end  60  of the support rod  52 . Accordingly, the aft end  60  of the support rod  52  is securely connected to the bottom end cap  16  so as to transmit tensile, compression, or bending loads between these two components of the load-bearing unit. 
     FIG. 5  is a cross-sectional view of the ammunition assembly  10  shown positioned in a firing device  70 . In use, the ammunition assembly  10  is inserted into the firing device&#39;s breech  72  and seated in the firing chamber  74  between the breech face  76  and barrel face  78 . The ammunition assembly  10  is then in a position ready to fire. Upon firing, the ignition device  36  ignites the main propellant bed  34  and begins combustion of the propellant and generation of a pressure wave and a flame front in the case body  12 . The gasses generated by the burning propellant bed  34  begin pressurizing the interior area  19  of the case body  12 . The pressure wave and flame front, upon reaching the combustible case body  12 , act to radially expand the combustible case body  12  and the elastomeric sealing rings  32  into contact with the firing chamber walls  80 , thereby sealing the walls from the propellant gases. 
   The flame front from the burning propellant ignites the case body  12  and begins consuming the case body in combustion. As the propellant and case body  12  continue to burn, the pressure in the firing chamber  74  greatly increases, thereby creating tension stress on the support structure  18 . This tension stress causes the support structure  18  to elastically deform axially within the firing chamber  74 . The majority of this elastic deformation is substantially isolated to the middle portion  53  of the support rods  52  because of the reduced diameter of the middle portions. The top and bottom end caps  14  and  16  also move axially and engage the barrel face  78  and the breech face  76 , respectively, thereby forming gas seals that prevent propellant gas leakage. The propellant bed  34  and the case body  12  are completely consumed within the firing chamber  74  and the pressures in the firing chamber drive the projectile  20  into the barrel  82  of the firing device  70 . In one embodiment, the projectile  20  is adapted to engage rifling grooves (not shown) in the barrel  82  to impart spin to the projectile, and in other embodiments the projectile is adapted for firing through a smooth-bore barrel. 
   After the projectile  20  is fired out of the barrel  82  and the pressure in the firing chamber  74  and breech  72  is dissipated, the support structure  18  contracts axially substantially to its pre-fired condition, thereby pulling the top and bottom end caps  14  and  16  out of engagement with the barrel face  78  and the breech face  76 , respectively. After firing, only the top and bottom end caps  14  and  16 , the support structure  18 , and ancillary items, such as the ignition device  36 , remaining in the firing chamber  74  are retracted into the breech  72  as a unitary spent unit. The spent unit is then ejected from the firing device  70  in an ejection cycle. The support structure  18  holds the top and bottom end caps  14  and  16  in axial alignment during the ejection cycle, thereby greatly minimizing the risk of a jam in the firing chamber  74  or the breech  72 , which would take the weapon out of service at least until the jam was cleared. 
   In one embodiment, the ammunition assembly  10  is usable in a gun or other firing device  70  having a firing chamber  74  configured to move out of alignment with the barrel face  78  and the breech face  76  in order to eject the unitary spent unit and load a fresh ammunition assembly  10 . The fresh ammunition assembly  10  is loaded into the firing chamber  74  by pushing it in from the rear of the now open firing chamber. The fresh ammunition assembly  10  is firmly and aggressively pushed against the unitary spent unit, thereby ejecting it out of the front of the firing chamber  74 . This reloading process typically creates a substantial axial impact and compressive load on the fresh ammunition assembly  10 , and this axial impact is reacted along the load path so the combustible case body  12  is not damaged during the loading process. Upon completion of this loading/ejection cycle, the firing chamber  74  is realigned with the barrel face  78  and the breech face  76 , and the chambered fresh ammunition assembly  10  is ready for firing. 
   From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for the purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.