Patent Abstract:
A metal tube provides a bearing for a bolt carrier in a rifle. The tube is machined to provide openings and co-molded with a polymer outer shroud to form a lightweight composite upper receiver. The tube has an inner surface that supports the bolt carrier in its reciprocal motion during cycling of the rifle action during firing. The length and diameter of the tube are designed to prevent tilt of the bolt carrier during operation.

Full Description:
FIELD OF THE INVENTION 
     This invention relates to rifles for military and civilian sporting use. 
     BACKGROUND 
     Modern sporting rifles as well as military rifles and carbines must be robust for reliable operation, and lightweight to permit carry without excessive fatigue. Significant reduction in rifle weight has been previously achieved by replacing wood with polymer material for components such as the shoulder stock and fore stock. Such designs have been successful because the use of polymer material for these elements does not compromise the robustness or reliable operation of modern firearms. 
     However, components such as the receiver and its associated assemblies such as the bolt carrier and barrel still account for a significant portion of the weight of a firearm, as it has not been thought feasible to substitute polymer for such parts which experience heat, pressure and wear from reciprocating motion. To meet the harsh requirements of operation many receiver designs are machined from a solid aluminum billet, and thus represent, in addition to significant weight, a significant production cost, as the machining is complex and constrained by tight tolerance requirements. There is clearly a need to further reduce rifle weight and simplify production without compromising the performance of the modern combat or sporting rifle. 
     SUMMARY 
     The invention concerns a bearing for a bolt carrier in an upper receiver of a firearm having a charging handle, a fire control mechanism and a magazine. In one example embodiment the bearing comprises a tube positionable within the upper receiver. The tube has a sidewall defining an inner surface supporting the bolt carrier and motion thereof between an open position and a battery position. A first opening in the sidewall defines an ejector port. A second opening in the sidewall is positioned to permit engagement between the bolt carrier and the charging handle. A third opening in the sidewall receives the fire control mechanism or the magazine. 
     By way of example a fourth opening in the sidewall receives the fire control mechanism or the magazine. In an example embodiment, the tube has a buffer tube radius for attaching a buffer tube to the tube. In a specific example the second opening is positioned diametrically opposite to the third opening. In a further specific example the second opening is positioned diametrically opposite to the fourth opening. In another example the first opening is positioned angularly offset from the second opening about a longitudinal axis of the tube. In an example embodiment the second opening comprises a slot extending lengthwise along the tube, one end of the slot being open. In a further example the third and fourth openings are contiguous with one another. In another example the fourth opening is wider than the third opening. 
     By way of example one end of the tube comprises screw threads. In a particular example the screw threads are positioned on the inner surface. In another example the screw threads are positioned on an outer surface of the tube. An example embodiment further comprises an aperture in the sidewall for permitting engagement between the bolt carrier and a forward assist button. 
     The invention also encompasses an upper receiver of a firearm having a bolt carrier, a charging handle, a fire control mechanism and a magazine. In this example embodiment the upper receiver comprises a metal tube having a sidewall defining an inner surface supporting the bolt carrier and motion thereof between an open position and a battery position. A polymer shroud surrounds at least a portion of the metal tube. A first opening, positioned in the sidewall and a first opening, positioned in the polymer shroud overlying the first opening in the sidewall define an ejector port. 
     By way of example the invention further comprises a second opening in the sidewall and a second opening in the polymer shroud overlying the second opening in the sidewall. The second openings are positioned to permit engagement between the bolt carrier and the charging handle. 
     An example embodiment further comprises a third opening in the sidewall for receiving the fire control mechanism or the magazine. Another example comprises a fourth opening in the sidewall for receiving the fire control mechanism or the magazine. Another example embodiment comprises a rail mounted on the shroud. The rail and extends lengthwise along the tube and comprises a plurality of ribs oriented transversely to a longitudinal axis of the tube. Further by way of example the shroud comprises an outwardly projecting surface positioned adjacent to the ejector port. Another example further comprises a housing extending from the shroud for receiving a forward assist button. In this example the metal tube comprises an aperture aligned with the housing for permitting engagement between the bolt carrier and the forward assist button. 
     By way of example the invention further comprises first and second lugs positioned at opposite ends of the shroud for attaching the shroud to a lower receiver. Another example embodiment of the invention comprises a buffer tube radius for attaching a buffer tube to the metal tube. 
     By way of example, the first openings are positioned angularly offset from the second openings about a longitudinal axis of the metal tube. In a further example, the second opening in the sidewall of the metal tube comprises a slot extending lengthwise along the metal tube, one end of the slot being open. 
     In an example embodiment, one end of the metal tube comprises screw threads. In a specific example the screw threads are positioned on the inner surface of the metal tube. In another example embodiment, the screw threads are positioned on an outer surface of the metal tube. 
     The invention also encompasses firearm having a bolt carrier, a charging handle, a fire control mechanism and a magazine. In an example embodiment the firearm comprises an upper receiver comprising a metal tube having a sidewall defining an inner surface supporting the bolt carrier and motion thereof between an open position and a battery position. A polymer shroud surrounds at least a portion of the metal tube. A first opening is positioned in the sidewall and a first opening in the polymer shroud overlies the first opening in the sidewall. The first openings define an ejector port. 
     In an example embodiment a second opening in the sidewall and a second opening in the polymer shroud overlying the second opening in the sidewall are positioned to permit engagement between the bolt carrier and the charging handle. 
     In another example a third opening in the sidewall receives the fire control mechanism or the magazine. In a further example the invention comprises a fourth opening in the sidewall for receiving the fire control mechanism or the magazine. In a specific example embodiment a rail is mounted on the shroud and extends lengthwise along the tube. The rail comprises a plurality of ribs oriented transversely to a longitudinal axis of the tube. By way of example the shroud further comprises an outwardly projecting surface positioned adjacent to the ejector port. 
     In an example embodiment the firearm further comprises a housing extending from the shroud for receiving a forward assist button. The metal tube comprises an aperture aligned with the housing for permitting engagement between the bolt carrier and the forward assist button. 
     By way of further example, first and second lugs are positioned at opposite ends of the shroud for attaching the shroud to a lower receiver. A particular example comprises a buffer tube radius for attaching a buffer tube to the metal tube. In a specific example the first openings are positioned angularly offset from the second openings about a longitudinal axis of the metal tube. In another example the second opening in the sidewall of the metal tube comprises a slot extending lengthwise along the metal tube, one end of the slot being open. By way of example, one end of the metal tube comprises screw threads. In a specific example the screw threads are positioned on the inner surface of the metal tube. In another example, the screw threads are positioned on an outer surface of the metal tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a right side view of an example rifle according to the invention; 
         FIG. 1A  is a longitudinal sectional view taken from within the ellipse of  FIG. 1 ; 
         FIG. 2  is a right side view of the lower receiver of the rifle shown in  FIG. 1 ; 
         FIG. 3  is a right side view of the upper receiver of the rifle shown in  FIG. 1 ; 
         FIG. 4  is an exploded side view of the upper receiver of the rifle shown in  FIG. 1 ; 
         FIG. 5  is an isometric view of an example bearing used in an upper receiver of a rifle; 
         FIG. 6  is an isometric view of the bearing shown in  FIG. 5  rotated 90° about its longitudinal axis in a clockwise direction; and 
         FIG. 7  is an isometric longitudinal sectional view of a portion of an example upper receiver according to the invention; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts an example embodiment of a rifle  10  according to the invention. Rifle  10  may be capable of automatic or semi-automatic operation and comprises a lower receiver  12  (see also  FIG. 2 ) which houses a fire control mechanism  14  (see also  FIG. 4 ) and has a magazine well  16  which receives an ammunition magazine  18 . An upper receiver  20  (see also  FIG. 3 ) is attached to the lower receiver  12 . The upper receiver houses a charging handle  22 , a bolt carrier  24  (see also  FIG. 4 ) and may also house a forward assist button  26 . 
     During operation of the rifle  10 , the bolt carrier  24  (see  FIG. 4 ) reciprocates within the upper receiver  20  between “battery”, a position wherein the bolt  28  on the bolt carrier  24  is engaged with the breech of barrel  30  (see  FIG. 1A ), and an open position, where the bolt  28  is disengaged from the breech and the bolt carrier  24  is retracted away from the breech. In battery, a round chambered in the breech may be discharged. Upon discharge, the bolt carrier  24  moves from battery to the open position, extracting and ejecting the spent cartridge and resetting the fire control mechanism  14  along the way. Motion of the bolt carrier  24  from battery to the open position also compresses a return spring (not shown) acting on the bolt carrier. As the bolt carrier  24  moves back into battery (driven by the return spring) it strips a round from the magazine  18  and chambers it in the breech of barrel  30  completing the cycle. Energy for moving the bolt carrier  24  through this cycle (in either automatic or semi-automatic operation) is provided by the ammunition itself using one of at least three well understood modes of operation commonly known as “recoil”, “blow-back”, and “gas” operation. A round is initially chambered and the fire control mechanism  14  is initially set by drawing and releasing the charging handle  22 , which draws the bolt carrier  24  from battery to the open position and permits the bolt carrier to move back into battery, driven by the aforementioned return spring (not shown). 
     Thus the upper receiver  20  must support the bolt carrier  24  as it moves between battery and the open position but also allow the various components, including the fire control mechanism  14 , the magazine  18 , the charging handle  22 , and the forward assist button  26  (when present) to interact with the bolt carrier. The upper receiver  20  must also provide an ejection port  32  to permit ejection of the spent cartridge. In the upper receiver  20  according to the invention the bolt carrier  24  is supported by a bearing  34 , shown in  FIGS. 4-6 . Bearing  34  comprises a metal tube  36 , which may be formed from aluminum, steel or other durable metals. Tube  36  in this example has a round cross section defined by a sidewall  38 . Sidewall  38  also defines an inner surface  40  which supports the bolt carrier  24  in its reciprocal motion between battery and the open position. Tube  36  is sized in both length and inner diameter so that tilting of the bolt carrier  24  relative to the longitudinal axis  52  of tube  36  is mitigated to ensure smooth motion during operation for reliability. 
     As shown in  FIGS. 4 and 5 , an ejector port  42  is provided within the sidewall  38  to permit ejection of spent cartridges from the receiver. An aperture  44  is also provided within the sidewall  38  to permit the forward assist button  26  to engage the bolt carrier  24  and drive it into battery when the return spring fails to do so.  FIG. 5  illustrates yet another opening  46  in the sidewall  38  which is positioned to permit the charging handle  22  to engage the bolt carrier  24 .  FIG. 6  illustrates additional openings  48  and  50 . Opening  48  permits at least a portion of the fire control mechanism  14  (see  FIG. 4 ) to extend into the tube  36  and interact with the bolt carrier  24 . Opening  50  permits the magazine  18  to extend into the tube  36  so that rounds can be stripped and chambered as the bolt carrier  24  moves into battery. 
     As shown by way of example in  FIGS. 5 and 6 , the opening  46  for charging handle  22  is diametrically opposite to the openings  48  and  50  for the fire control mechanism  14  and the magazine  18 . This configuration is dictated by the layout of the rifle  10  shown in  FIG. 1 , wherein the charging handle  22  is positioned on the upper receiver  20  and substantially aligned with the fire control mechanism  14  and the magazine well  16  which receives the magazine  18 , all of which are housed in the lower receiver  12 . Ejector port  42  (see  FIGS. 4 and 5 ) is angularly offset from the charging handle opening  46  about the longitudinal axis  52  of the tube  36  to direct the spent cartridges to the right side of the rifle  10 . Other arrangements of the openings in tube  36  are of course feasible to accommodate other rifle configurations. The openings are further shaped and dimensioned commensurate with their respective functions. To this end, opening  46  in this example comprises an elongate slot to accommodate the necessary range of motion of the charging handle  22  and bolt carrier  24  along the tube  36 . In this example one end  46   a  of the slot formed by opening  46  is open. Similarly, openings  48  and  50  are sized to accommodate the fire control mechanism and magazine, respectively, opening  50  being wider than opening  48  as a result. The openings  48  and  50  may be contiguous with one another as shown. 
     The simplicity of the bearing  34  allows the various openings to be conveniently formed by laser machining techniques. Traditional machining techniques are of course also feasible. 
     As further shown in  FIG. 1A , tube  36  may have screw threads  54  positioned at the end which interfaces with the barrel  30  (see also  FIG. 1 ). Threads  54  may be on the inner surface  40  of the tube  36  (shown) or on the outer surface  56 . Additionally, as shown in  FIG. 6 , a buffer tube radius  56  may also be part of tube  36  for accommodating a buffer tube (not shown), which contains the return spring (not shown). 
     Another part of the upper receiver according to the invention is the polymer shroud  58 , an example being shown in  FIG. 4 . Shroud  58  is formed from a polymer such as fiber reinforce nylon which, as shown in  FIGS. 3 and 7 , is injection molded around a tube  36  that has already been machined and finished. In production a machined, finished tube  36  is placed in a mold for the upper shroud, the mold is closed, and the polymer is injected into the mold in a co-molding process that joins shroud and tube. Injection molding is advantageous because it permits features having complex geometries to be incorporated into the upper receiver while avoiding costly and time consuming machining. The example shroud  58  includes a so-called “Picatinny” rail  60  that extends lengthwise along the tube  36  and has a plurality of transverse ribs  62 . Also shown in  FIG. 3  are a housing  64  for the forward assist button  26  and an outwardly projecting surface  66  adjacent to the ejector port  42  for deflecting ejected cartridges. Lugs  68  for attaching the upper receiver  20  to the lower receiver  12  may also be injection molded as part of shroud  58 . 
     Injection molding also allows openings to be formed in the shroud  58  that correspond to openings in the tube  36 . As shown in  FIGS. 3 and 4 , opening  70  in shroud  58  aligns with the ejector port opening  32  in the tube  36 ; opening  72  in the shroud aligns with the opening  46  for the charging handle  22 ; and opening  74  aligns with aperture  44  for the forward assist button  26 . In the example shroud  58  the region between the lugs  68  is substantially open to permit the fire control mechanism  14  and the magazine  18  to be received within respective openings  48  and  50  in the sidewall  38  of tube  36  when the upper receiver  20  is mounted on the lower receiver  12  and the magazine  18  is inserted into magazine well  16 . 
     A rifle having a polymer upper receiver co-molded with a tube comprising a bearing for supporting and guiding a bolt carrier provides numerous advantages over traditional rifles wherein the receiver is machined from a billet. Such rifles will have reduced weight and more economical and rapid production without sacrificing reliability or robustness.

Technology Classification (CPC): 5