Patent Publication Number: US-8539708-B2

Title: Barrel mounting and retention mechanism

Description:
TECHNICAL FIELD 
     Embodiments of the disclosure are directed generally to gas operated firearms and, more particularly, to an apparatus for mounting a barrel to the receiver of a gas-operated firearm. 
     BACKGROUND INFORMATION 
     Semi-automatic firearms, such as rifles and shotguns, are designed to fire a round of ammunition, such as a cartridge or shot shell, in response to each squeeze of the trigger of the firearm, and thereafter automatically load the next shell or cartridge from the firearm magazine into the chamber of the firearm. During firing, the primer of the round of ammunition ignites the propellant inside the round, producing an expanding column of high pressure gases within the chamber and barrel of the firearm. The force of this expanding gas propels the bullet/shot of the cartridge or shell down the barrel. 
     In some types of semi-automatic rifles and shotguns, a portion of the expanding gases will be directed through a duct or port that interconnects the barrel of the firearm to a gas operating system, such as a piston assembly that houses an axially moveable gas piston, or a gas impingement system that directs the expanding gases to impinge on a bolt assembly within a receiver of the firearm. The barrel and the gas operating system typically are coupled to the receiver and aligned with the bolt assembly of the firearm so that the gas operating system can act on the bolt assembly as part of the semi-automatic loading and operation of the firearm so as to cause the rearward motion of the bolt assembly. This rearward motion of the bolt assembly opens the chamber, ejects the empty shell or cartridge casing, and thereafter loads another shell or cartridge into the chamber, after which the bolt returns to a locked position for firing as the expanding gases dissipate or are bled off. The barrel further must be connected in alignment with the gas system to facilitate proper operation of the gas system. 
     In addition, in such semi-automatic and automatic firearms, it is desirable that the barrel be easily replaceable to enable change of calibers of ammunition to be used in the firearm and/or to provide for replacement of damaged barrels or use of barrels of different lengths for different end use scenarios. The changeout of barrels is, however, complicated by the use of various hand guards and accessory rail assemblies typically mounted about the barrels of such firearms, as well as the increasing use of monolithic or one-piece receiver and hand guard assemblies. Typically, such hand guards must be removed from the firearm prior to the removal and replacement of the barrel, increasing the difficulty and time required for barrel change-out. 
     Accordingly, it can be seen that a need exists for a barrel mounting and retention assembly that addresses the foregoing and other related and unrelated problems in the art. 
     SUMMARY OF THE DISCLOSURE 
     Briefly described, in one embodiment of the invention, a barrel mounting and retention device is provided for use with a gas-operated firearm. The barrel mounting and retention device can comprise a barrel extension defining a first axial bore and being disposed at a proximal end of the barrel, the barrel defining a chamber at least partially extending in the proximal end. An annular collar can be formed about a forward or first portion of the barrel extension and will comprise a first clamp face. At least a portion of the first clamp face can comprise a first oblique portion extending in an oblique direction with respect to a longitudinal axis of the barrel. A mounting plate, including a second clamp face and defining a second axial bore through which the barrel is received and extends will be received about the barrel and will engage the front face of the barrel extension. 
     At least a portion of the second clamp face comprises a second oblique portion extending in an oblique direction with respect to the longitudinal axis of the barrel. At least a portion of the second oblique portion is adopted to engage/abut at least a portion of the first oblique portion in a complimentary fitting engagement as the mounting plate is secured to and urged against a face of the receiver of the firearm by insertion of fasteners through a series of mounting bores formed about the periphery of the mounting plate. As the fasteners are tightened, urging the mounting plate toward the receiver, a clamping force is applied to the barrel extension and the annular collar. Any misalignment of the bores or fasteners is generally corrected by the engagement of the first and second clamp faces such that the clamping force applied to the barrel extension, and thus the barrel, is aligned and substantially maintained in a straight line with the longitudinal axis of the barrel. An alignment feature also can be provided extending from the barrel extension, for aligning the barrel extension with the receiver. 
     These and various other advantages, features, and aspects of the exemplary embodiments will become apparent and more readily appreciated from the following detailed description of the embodiments taken in conjunction with the accompanying drawings, as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view, with parts broken away for clarity, of a gas-operated firearm with a barrel mounting and retention device according to an exemplary embodiment of the disclosure. 
         FIG. 2  is an isometric view of a gas operating system, a barrel extension, a mounting plate, and the barrel of  FIG. 1 . 
         FIG. 3  is an exploded isometric view of the barrel extension, the mounting plate, the barrel, and the gas operating system. 
         FIG. 4  is an isometric view of the barrel extension. 
         FIG. 5  is an isometric view of the barrel extension and the mounting plate aligned with the operating rod of the gas operating system. 
         FIG. 6  is a cross-sectional view of the barrel extension and the mounting plate, and operating rod of the gas operating system. 
         FIG. 7  is a cross-sectional view of another embodiment of the barrel extension and the mounting plate engaged with a gas impingement tube of an alternative gas operating system. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Referring now to the drawings in which like numerals indicate like parts throughout the several views, the figures illustrate one example embodiment of the barrel mounting and retention apparatus or system according to the principles of the present disclosure for use in a firearm such as an M4, M16, AR-15, SCAR, AK-47, HK416, ACR or similar type gas operated firearm. However, it will be understood that the principles of the barrel mounting and retention device of the present invention can be used in various types of firearms including shotguns, rifles and other long guns, hand guns, and other gas-operated firearms. The following description is provided as an enabling teaching of exemplary embodiments; and those skilled in the relevant art will recognize that many changes can be made to the embodiments described. It also will be apparent that some of the desired benefits of the embodiments described can be obtained by selecting some of the features of the embodiments without utilizing other features. Accordingly, those skilled in the art will recognize that many modifications and adaptations to the embodiments described are possible and may even be desirable in certain circumstances, and are a part of the invention. Thus, the following description is provided as illustrative of the principles of the embodiments and not in limitation thereof, since the scope of the invention is defined by the claims. 
       FIG. 1  illustrates a gas-operated firearm  10  showing a gas operating system with a barrel mounting and retention device in one exemplary embodiment. The firearm  10  generally is shown as a rifle, with parts broken away for clarity, and includes a barrel  12  with a longitudinal axis L ( FIG. 2 ), an upper receiver  14 , lower receiver or chassis  15  including a fire control  16 , a stock  18 , a gas operating system  20  with a gas block  30 , and a barrel mounting and retention device  40 . Further, a hand guard assembly  200  can be affixed to and/or utilized with the firearm  10 . Alternatively, any other type of hand guard can be affixed to and/or utilized with the firearm  10 , or a hand guard can be omitted from the firearm. For example, the firearm can incorporate a monolithic, integral upper-style receiver and hand guard, wherein the hand guard is integrally formed with the receiver, or an AR-style two-piece receiver and hand guard. The stock  18 , also known as the buttstock or shoulder stock, may be formed in any conventional manner to include cushioning, special curvatures, grips, in a holding stock portion, etc. The upper receiver  14  houses and includes the firing mechanism or fire control  16  of the firearm, including a trigger  17  for actuating the firearm, a breech bolt or bolt assembly, and a firing pin is shown. The bolt assembly is translatable axially in both forward and rearward directions along the receiver during the firing cycle and generally is located behind and communicates with a chamber portion  19  ( FIG. 3 ) of the barrel  12 , located at a proximal end of the barrel  12  adjacent or at least partially within the receiver  14 . The chamber receives a round of ammunition R, such as a shell or cartridge for firing, typically from a magazine M ( FIG. 1 ) received within the lower receiver  15 . 
     In the gas-operated semi-automatic firearm  10  illustrated in  FIGS. 1 and 2 , the gas operating system  20  is shown in one embodiment as including a gas-operated piston assembly  21  for operation of the firearm for ejecting a spent shell or casing and reloading the chamber after firing by way of mechanical interconnection and interaction between the piston assembly  21  and the bolt assembly of the firearm. During a firing operation, a portion of the expanding combustion gases from the barrel is directed into the gas block  30  of the gas operating system  20 , which gas flow accordingly contacts and drives the gas piston  22  rearwardly. This rearward movement or action of the gas piston  22 , in turn is translated to the bolt, to cause a spent cartridge/shell casing to be automatically cleared or ejected from the chamber  19 , a new round R to be loaded into the chamber, and the hammer and bolt to be recocked and readied for a next firing cycle. 
     As shown in  FIGS. 2 and 3 , the gas operating system  20  includes gas piston  22  housed within gas block  30 , an operating rod  24  adapted to be engaged by the piston  22  during operation, and a gas plug  26  adapted to be received within and housed by the gas block  30 . The gas block  30  further includes a barrel band  32  adapted to fit over and clamp about the barrel  12  to secure the gas operating system thereto, and a gas block bore  34  extending longitudinally there through. The barrel band  32  engages the barrel  12 , abutting a shoulder portion  12   a  thereof so that a gas port of the barrel (not shown) generally aligns with a gas port or inlet (not shown) for the gas block bore  34 , which extends through the gas block between the barrel gas port and the gas block bore. The aligned barrel orifice and gas port enable a portion of the combustion gases generated during firing to communicate from the bore of the barrel  12  into the gas block bore  34 . 
     As shown in  FIG. 3 , the operating rod  24  of the firearm&#39;s gas operating system  20  generally is located rearwardly of the gas piston in a position aligned with and adapted to be engaged by a first end  22   a  of the gas piston  22  as the gas piston slides along the gas block bore  34  of the gas block housing after firing, with both the operating rod and the gas piston being slideable within the gas block bore and along the gas block for a desired amount of travel. The operating rod  24  ( FIGS. 1 and 2 ) extends beyond the rearward end  35  of the gas block bore  34  and through the barrel mounting and retention device  40 , as described below for engaging the bolt assembly in the receiver  14 . A piston return spring  24   a  can be concentrically mounted on the operating rod  24 , engaging a rod shoulder  24   b  and the barrel mounting and retention device  40  in order to bias the operating rod  24  and the gas piston  22  forwardly. Alternatively or in addition, the gas piston also can be spring biased toward its forward, non-operative position. The gas piston  22  can be biased to a position where a reduced diameter portion  22   b  of the gas piston, or other portion capable of receiving the gases, is generally aligned with the gas port so as to enable a passage of gases from the barrel into the gas block bore  34 . 
     As further indicated in  FIG. 2 , the gas plug  26  fits within the open forward end of the gas block in sealing engagement with the gas block bore  34 . The incoming flow of exhaust or combustion gases can act against the gas plug  26  and the second upstream end  22   c  ( FIG. 3 ) of the piston so as to cause the gas piston  22  to move the gas piston rearwardly along the gas block bore  34 . Additional details of an exemplary gas piston, an exemplary gas operating system in general, and an exemplary firearm incorporating the same are included in co-pending U.S. patent application Ser. No. 12/818,291, filed Jun. 18, 2010, which application is hereby incorporated by reference for all purposes as if presented herein in its entirety. 
     As shown in  FIGS. 1-3 , the barrel mounting and retention device  40  includes a barrel extension  42  and a mounting plate  44  that cooperate to secure and retain the barrel  12  in abutting engagement with the receiver  14 . As shown in  FIGS. 4 and 5 , the barrel extension  42  generally includes a cylinder section  46  and an annular boss or collar  48 . The cylinder section  46  will include an axial bore  50  extending from a bolt-receiving end  52  of the barrel extension to a barrel-receiving end  54  adjacent the collar  48 . As shown in  FIG. 4 , the axial bore  50  can include a bolt interlocking section  56  ( FIG. 6 ) adjacent the bolt-receiving end  52  and a threaded section  58  extending from the bolt interlocking section  56  to the barrel-receiving end  54  for engaging external threads  59   a  formed about a proximal end  59  or the chamber portion  19  of the firearm. The cylinder section  46  can slide axially into the receiver  14  ( FIG. 1 ) to interface with the bolt assembly of the firearm  10 . 
     As shown in  FIGS. 4 and 6 , the bolt-receiving end  52  further includes a plurality of locking lugs  60  extending radially into the axial bore  50  with recesses  62  formed between the locking lugs  60 . The bolt assembly generally will include a breach bolt having a plurality of corresponding lugs and recesses at its forward end, with the lugs of the breach bolt engaging the recesses  62  of the barrel extension  42  while the locking lugs  60  of the barrel extension  42  engage the recesses of the breach bolt when the forward end of the breach bolt is passed through the bolt-receiving end  52  and into the interlocking section  56  of the barrel extension when chambering a round R into the chamber  15 . Thereafter, with the lugs of the breach bolt received within the interlocking section  56 , the bolt assembly can rotate to at least partially align the lugs of the breach bolt with the locking lugs  60  to lock the bolt assembly to the barrel extension  42  for firing the firearm  10 . After a firing operation, the bolt assembly will rotate in an opposite direction as it moves rearwardly so that the lugs of the breach bolt are aligned with the recesses  62  and the breach bolt can withdraw from the barrel extension  42  to extract a spent shell or cartridge casing from the chamber and chamber another round. 
     As shown in  FIG. 3 , the threaded section  58  of the axial bore  50  can receive the proximal end  59  of the barrel  12 , which includes at least a portion of the chamber  19 . The threaded section  58  can be threaded for interfacing with the external threads  59   a  formed about the proximal end  59  of the barrel  12  for attaching the barrel to the barrel extension. An annular barrel stop shoulder  64  ( FIG. 5 ) further can be formed at the barrel-receiving end  54  of the axial bore  50 , as indicated in  FIGS. 5-6 , for engaging and abutting against a shoulder  66  ( FIGS. 3 and 6 ) proximate the external threads  59   a  of the barrel  12  when the barrel extension barrel  42  is in engagement with the proximal end  59  of the barrel ( FIG. 2 ). Alternatively, the annular barrel stop shoulder  64  ( FIG. 5 ) can be omitted, and the rearward face of the shoulder  66  can engage a forward face of the threads formed at the barrel-receiving end  54  of the barrel extension. 
     As shown in  FIGS. 4 and 5 , the collar  48  of the barrel extension  42  is shown abutting the annular barrel stop shoulder  64 , and generally includes a rearward face  68 , a clamp face  70  with a generally oblique surface, here shown as a convex spherical surface  72 , and a rod-receiving flange  74 . The rearward face  68  extends outwardly from the cylinder section  46  in the radial direction to provide a generally flat rearward facing surface for engaging the forward facing surface  75  of the receiver  14  ( FIG. 1 ). Accordingly, a clamp force applied along the longitudinal axis L of the barrel  12  tends to urge the rearward face  68  against the forward surface  75  of the receiver. The generally flat nature of the rearward face  68  allows proper seating of the collar  48  against the receiver  14  for secure retention of the barrel extension  42 , and thus the barrel  12 , to the receiver  14 , as well as proper alignment of the longitudinal axis L of the barrel  12  with a longitudinal axis of the receiver, with minimal effort by a user. No additional tools are required for alignment of the barrel and the receiver. In the illustrated embodiment, the convex spherical surface  72  extends in an oblique direction with respect to the longitudinal axis L of the barrel  12 , projecting generally away from the receiver  14  from the inner radius to the outer radius of the convex spherical surface  72 . Further, in the illustrated embodiment, the convex spherical surface  72  includes a convex, curved cross-section. In an alternative embodiment, the convex spherical surface  72  can be any surface that extends in an oblique direction with respect to the longitudinal axis L of the barrel  12 . 
     The rod-receiving flange  74  includes a through-bore  76  for aligning the operating rod  24  with the opening in the receiver  14 . The rod-receiving flange  74  can provide a bearing and/or guide surface  77  for supporting the operating rod  24  as it reciprocates during the operation of the firearm  10 . An optional bushing  78  ( FIG. 3 ) also can be inserted into the through-bore  76  of the rod-receiving flange  74  to provide the bearing surface. Additionally, as indicated in  FIG. 1 , when the barrel extension  42  is mounted in engagement with the receiver  14 , the rod-receiving flange generally becomes aligned with a corresponding opening  79  in the receiver so that the operating rod  24  can extend into the receiver and either directly or indirectly engage the bolt assembly. Alternatively, the bore of the rod-receiving flange  74  can be formed with a sufficient size to provide clearance for the operating rod  24  to pass through and into the receiver  14 , or the rod-receiving flange  74  could be omitted so that the operating rod  24  passes directly into the receiver  14  without engaging the barrel extension  42 , without departing from the scope of the present disclosure. Three or more longitudinal recesses  80  further can be included in the collar  48  for providing guide surfaces and/or clearance for insertion of mechanical fasteners  92  there through to secure the barrel mounting apparatus  40  to the receiver  14  ( FIG. 1 ). 
     As illustrated in  FIGS. 3 ,  5 , and  6 , the mounting plate  44  can include an axial bore  82 , a rear mounting plate face  84  with a generally oblique engagement surface, here shown as a concave spherical surface  86 , a rod-receiving flange  88 , and four recesses or bores  90  generally are arranged around the axial bore  82  though fewer or more holes also can be provided. The axial bore  82  provides clearance for the shoulder  66  of the barrel  12  to pass through and engage the barrel extension  42 . Accordingly, the mounting plate  44  can slide over and along the barrel  12  to engage the collar  48 , as shown in  FIGS. 1 and 2 . In the illustrated embodiment, the concave spherical surface  86  extends in an oblique direction with respect to the longitudinal axis L of the barrel  12 , projecting generally toward the receiver  14  from the inner radius to the outer radius of the concave spherical surface  86 . Further, in the illustrated embodiment, the concave spherical surface  86  comprises a concave, curved cross-section. In an alternative embodiment, the concave spherical surface  86  can be any surface that extends in an oblique direction with respect to the longitudinal axis L of the barrel  12 . In a further alternative embodiment, any of the features of the clamp face  70  of the collar  48  can be exchanged with the respective features of the clamp face  84  of the mounting plate  44 . For example, the clamp face  70  of the collar can include an oblique surface extending toward the receiver  14  and the clamp face  84  of the mounting plate can include an oblique surface extending away from the receiver  14 . 
     The concave spherical surface  86  interfaces with the convex spherical surface  72  of the collar  48  to provide a straight-line clamping force between the mounting plate  44  and the barrel extension  42  while correcting for any misalignment of the bores  90 . Stated another way, the interfacing convex and concave surfaces tend to align the axial bore  50  of the barrel extension  42  with the axial bore  82  of the mounting plate  44  and counter any forces that would otherwise move the axial bores out of alignment. For example, if any one or more mechanical fastener inserted through bores  90  create or apply an unequal force to one side of the mounting plate  44 , the convex spherical surface  72  of the collar  48  applies a reaction force to the concave spherical surface  86  of the mounting plate  44 , causing the mounting plate to shift or adjust to counter the excess force of the fastener(s). Further, if the mounting plate  44  is urged against the collar  48  with the axial bore  82  misaligned with the axial bore  50 , the curved surface of the clamp face  84  of the mounting plate will tend to slide against the curved surface of the clamp face  70  of the collar until the convex surface is properly seated in the concave surface thereby aligning the clamping force with the axial bore  50 . In the illustrated embodiment, each of the convex spherical surface  72  and the concave spherical surface  86  can have a gradual curvature to its cross-section ( FIG. 6 ), wherein, if the edges of the respective surfaces are extended along the same degree of curvature, each of the surfaces would form a substantially complete sphere. Alternatively, each of the convex spherical surface  72  and the concave spherical surface  86  could be replaced with a straighter or substantially flatter surface extending in an oblique direction with respect to the longitudinal axis of the barrel mounting and retention device  40 . 
     Each of the bores  90  provides clearance for a fastener  92  ( FIG. 1 ), such as cap screws or other mechanical fasteners. Alternatively, more or fewer fasteners  92  can be used in conjunction with a corresponding number of bores  90  in the mounting plate  44  and recesses  80  in the collar  48 , which also can be arranged in various patterns around the respective axial bores  82 ,  50  of the mounting plate and collar, without departing from the scope of the present disclosure. 
     The rod-receiving flange  88  further can include a clearance bore  94  along an upper edge, which clearance bore will generally be aligned with the through-bore  76  of the rod-receiving flange  74  of the collar  48  when the axial bore  82  of the mounting plate is aligned with the axial bore  50  of the barrel extension  42  by the interfacing convex spherical surface  72  and concave spherical surface  86  described above. Accordingly, the operating rod  24  can extend through the clearance bore  94  to the rod-receiving flange  74  of the collar  48 . The rod-receiving flange  88  additionally can include a spring seat  96  ( FIGS. 5 and 6 ) for receiving the proximal end of the spring  24   a . Accordingly, the spring  24   a  can rest/engage the mounting plate within the seat  96 , and will bear against the rod-receiving flange  88  and the rod shoulder  24   b  during operation of the gas operating system  20 . Alternatively, the rod-receiving flange  88  also can provide a bearing surface for supporting the operating rod  24 , or the rod-receiving flange  88  could be omitted so that the operating rod  24  passes into the through-bore  76  without engaging the mounting plate  44 , without departing from the scope of the present disclosure. 
     In the illustrated embodiment of  FIG. 5 , the mounting plate  44  is shown as including substantially concave cutouts  98  for reducing the size and weight of the mounting plate  44  while providing areas  93  in increased size for formation of the bores  90  and surfaces for engaging the mechanical fasteners  92  inserted through the bores at the corners  99  of the mounting plate. Alternatively, the mounting plate  44  can have any shape capable of fitting within the firearm without departing from the scope of the disclosure. 
     As shown in  FIG. 3 , the firearm  10  is at least partially assembled by inserting the proximal end  59  of the barrel  12  into the axial bore  82  of the mounting plate  44  with the clamp face  84  of the mounting plate directed rearwardly and away from the muzzle and or down-bore section  12   b  of the barrel. The proximal end  59  of the barrel then will be inserted into the barrel extension  42  at the barrel-receiving end  54  thereof, and threads  59   a  of the proximal end  59  engaged with the threads of the threaded section  58  of the cylinder section  46 . The barrel extension  42 , the barrel  12 , or both generally are rotated about their respective axes so as to screw the proximal end  59  of the barrel into engagement with the threaded section  58  until the shoulder  66  of the barrel  12  engages the barrel extension  42  at the barrel receiving end  54 . The proximal end  59  of the barrel can be screwed into the threaded section  58  with sufficient torque so that the friction between the contacting surfaces of the barrel  12  and the barrel extension  42  resists loosening of the proximal end of the barrel from the engagement within the axial bore  50 . In a particular embodiment, the proximal end can be further secured to the barrel extension  42  with adhesives, set screws, other fasteners, or combinations thereof, although such additional attachment devices are not required with the present invention. Accordingly, the proximal end  59  ( FIG. 3 ) of the barrel  12  is received within the axial bore  50  with the open end of the chamber portion  19  ( FIG. 1 ) adjacent the interlocking section  56 . 
     The cylinder section  46  of the barrel extension  42  can be inserted into the opening in the forward surface  75  of the receiver  14  until the rearward face  68  of the collar  48  engages the forward surface  75 . The forward surface  75  also can include an indexing recess  100  ( FIG. 1 ) that receives an indexing protrusion  102  of the rod-receiving flange  74  ( FIGS. 5 and 6 ). The indexing protrusion  102  can extend from the rearward face  68  of the collar  48  to engage the indexing recess  100  so that the through-bore  76  is aligned with the opening in the receiver  14  for receiving the gas operating rod  24 , whereupon the recesses  80  of the collar  48  further can become aligned with tapped holes  104  in the forward surface  75 , and the locking lugs  60  and recesses  62  will be aligned to receive the breach bolt of the bolt assembly within the receiver  14 . Alternatively, the indexing recess  100  and the indexing protrusion  102  can be otherwise configured or omitted without departing from the scope of the present disclosure. 
     In the illustrated embodiment, the mounting plate  44  is brought into engagement with the collar  48  so that the concave spherical surface  86  of the mounting plate abuts the convex spherical surface  72  of the collar ( FIG. 6 ) to align the clamping force of the mounting plate with the axial bore  50  of the barrel extension  42 . The mounting plate  44  can be rotated to align the clearance bore  94  with the through-bore  76 , and the mechanical fasteners  92  can be inserted into the bolt holes  90  ( FIG. 1 ). The fasteners  92  can slide over the respective guide surfaces of the recesses  80  to further align the bores  90  with the tapped holes  104  in the forward surface  75  of the receiver  14 . The fasteners  92  can be screwed into the tapped holes  104  to clamp the collar  48  between the mounting plate  44  and the forward surface  75 . Accordingly, the longitudinal clamping forces generated by the engagement of the fasteners  92  with the collar  48 , mounting plate  44  and the receiver secure the barrel extension  42  and the barrel  12  to the receiver  14 . Any misalignment of the bores  90  with the tapped holes  104  or any uneven torquing of the mechanical fasteners  92  that may apply a transverse force to the mounting plate  44  or the barrel extension  42 , which otherwise would cause a misalignment of the barrel and receiver, generally will be countered by the interface between the convex spherical surface  72  and the concave spherical surface  86  to maintain a generally straight-line clamping force between the mounting plate  44 , the collar  48 , and the forward surface  75  of the receiver  14 , which clamping force generally will be aligned with the longitudinal axis L of the barrel  12  of the firearm to maintain the barrel in a straight line orientation/alignment. For example, a transverse force applied to the mounting plate  44  by one or more of the mechanical fasteners  92  generally will be countered by a reaction force between the convex spherical surface  72  and the concave spherical surface  86  at an opposite side of the barrel mounting and retention device  40  from the particular mechanical fastener. Additionally, the illustrated embodiment, the collar  48  of the barrel extension  42  includes the convex spherical surface  72  and the clamp face  84  of the mounting plate  44  includes the concave spherical surface  86 , however, the collar  48  alternatively can be configured with a concave spherical surface, and the mounting plate  44  can be configured with a corresponding convex spherical surface without departing from the scope of the present disclosure. 
     As indicated in  FIGS. 2 and 3 , the gas operating system  20  will be secured to the barrel  12  by sliding the barrel band  32  of the gas block  30  over the barrel  12  until it abuts the shoulder portion  12   a . The gas block  30  is aligned with the barrel  12  to align gas ports (not shown) in the barrel and gas block to allow fluid communication between the interior of the barrel and the gas block bore  34 . The operating rod  24  and the piston return spring  24   a  are inserted into the gas block bore  34  so that the operating rod extends through the rearward end  35  of the gas block bore. The operating rod can be inserted through the clearance bore  94  of the rod-receiving flange  88 , the through-bore  76  of the rod-receiving flange  74 , and into the receiver  14  to engage the bolt assembly within the receiver. Accordingly, the rod-receiving flange  74 , which includes the indexing protrusion  102  engaging the indexing recess  100  in the receiver  14  for aligning the through-bore  76  with the opening in the receiver, automatically aligns the operating rod  24  with the opening in the receiver. This allows smooth operation of the operating rod into the receiver, and proper engagement of the operating rod with the bolt assembly within the receiver without requiring substantial effort by a user. Optionally, bushing  78  also can be inserted into the through-bore  76  of the rod-receiving flange  74  of the barrel extension  42  such as by a press fit, or additionally, by adhesives or other fasteners. Alternatively, this optional bushing can be omitted. The piston return spring  24   a  is generally situated on the operating rod  24  between and abutting the rod shoulder  24   b  and the rod-receiving flange  88  of the mounting plate  44 . The spring  24   a  can be further supported by the spring seat  96  of the mounting plate. The gas piston  22  and the gas plug  26  then will be inserted into the gas block bore  34  with the gas plug  26  sealing the forward end of the gas block bore ( FIG. 2 ). Alternatively, the gas operating system  20  can be assembled onto the barrel  12  and the barrel mounting and retention device  40  before affixing the barrel mounting and retention device  40  and barrel to the receiver  14  without departing from the scope of the present disclosure. 
     In operation, the firearm  10  ( FIG. 1 ) is prepared for firing when the bolt assembly loads a round of ammunition R in to the chamber portion of the firearm. The forward end of the breach bolt carries the round into the axial bore at the bolt-receiving end  52  of the cylinder section  46  and the lugs of the breach bolt pass through the recesses  62  between the locking lugs  60  at the bolt-receiving end  52 . With the lugs of the breach bolt in the interlocking section  56 , the round R is fully inserted into the chamber portion  19  of the barrel  12 , and the breach bolt rotates to align the lugs of the breach bolt with the locking lugs  60  at the bolt-receiving end  52  and lock breach bolt to the barrel extension  42  with the round in the chamber portion  19 . When the fire control  16  is actuated, a firing pin (not shown) strikes the primer of the round, igniting the propellant. Expanding gases from the ignited propellant build up pressure in the barrel  12 , driving the bullet portion of the round through the down bore section  12   b  of the barrel. Some of the expanding gases flow through the gas port (not shown) extending between the rifled section  12   b  and the gas block bore  34  to drive the gas piston  22  rearwardly in the gas block bore. The gas piston  22 , in turn, drives the operating rod  24  rearwardly against the piston return spring  24   a  and which drives the bolt assembly rearwardly within the receiver. The breach bolt then rotates within the interlocking section  56  in the axial bore  50  to unlock the lugs of the breach bolt from the barrel extension  42 , extracting the spent casing of the round R from the chamber and ejecting the spent casing from the firearm  10  after which a new round is loaded into the chamber. The piston return spring  24   a  thereafter drives the operating rod forwardly to return the gas piston  22  to the pre-firing position within the gas block bore  34 . 
     It should be noted that the firearm  10  alternatively could include a gas impingement operating system  20  ( FIG. 7 ) including a gas impingement tube  24 ′ for operation of the firearm for ejecting a spent shell or cartridge casing and reloading the chamber after firing by way of redirection of the expanding combustion gas flow to the bolt assembly of the firearm, instead of the piston-type gas operating system described above, without affecting the operation of the barrel mounting and retention device  40 . The gas impingement tube  24 ′ can be positioned within the gas block bore  34  ( FIG. 3 ) and extended beyond the rearward end  35  of the gas block bore and into the receiver  14  to the bolt carrier. Such a gas impingement tube  24 ′ generally would also include a flange (not shown) providing a sealing engagement with the gas block bore  34  so that the gas flow entering the gas block bore from the barrel  12  flows into and along the gas impingement tube so as to impinge on the bolt. 
     During a firing operation, a portion of the expanding combustion gases from the barrel is directed into the gas block  30 , which gas flow accordingly is directed rearwardly into the gas impingement tube  24 ′ ( FIG. 4 ), which terminates at a gas key of the bolt carrier. This rearward gas flow applies a rearward pressure on the bolt carrier, which functions to cause a spent cartridge/shell casing to be automatically cleared or ejected from the chamber, a new round of ammunition to be loaded into the chamber, and the firing pin and bolt to be recocked for a next firing cycle. 
     As shown in  FIG. 7 , the gas impingement tube  24 ′ extends through the clearance bore  94  of the rod-receiving flange  88  of the mounting plate  44  and through the through-bore  76  of the rod-receiving flange  74  of the collar  48  to the opening in the receiver  14 . Particularly, the through-bore  76  and the opening in the receiver are radially aligned by the engagement of the indexing protrusion  102  of the rod-receiving flange  74  with the indexing recess  100  in the forward surface  75  of the receiver, and axially aligned by engagement of the rearward face  68  of the collar  48  with the forward surface  75 . The clearance bore  94  and the through-bore  76  are radially aligned by engagement of the fasteners  92  extending through the bores  90  with the longitudinal recesses  80 , and axially aligned by the interface of the convex spherical surface  72  and the concave spherical surface  86 . Accordingly, the clearance bore  94  and the through-bore  76  will guide the gas impingement tube  24 ′ into the receiver  14  and support the gas impingement tube  24 ′ so that the gas impingement tube  24 ′ is properly aligned with the receiver and the bolt assembly therewithin. One or both of the rod-receiving flanges  88 ,  94  can be alternatively configured or omitted without departing from the scope of the present disclosure. 
     In addition, variations of the piston-type and gas impingement-type gas operating systems can be used in cooperation with the barrel mounting and retaining device  40 . For example, while the gas operating system  20  is generally oriented above the barrel  12  in the illustrated embodiment, the gas operating system can alternatively be oriented at any position around the barrel. Particularly, the gas block  30  can be oriented with the gas block bore  34  situated below the barrel  12  with the operating rod  24  or gas impingement tube  24 ′ extending from the rearward end  35  below the barrel. In such an alternative embodiment, the barrel extension  42  and the mounting plate  44  also generally will be oriented with the rod-receiving flanges  74 ,  88  below the barrel to receive the operating rod  24  or gas impingement tube  24 . Further, the gas block  30  shown and described is included by way of example. Alternative gas block configurations can be used without departing from the scope of the present disclosure. 
     In still a further alternative embodiment, the barrel extension  42  can be integral with the barrel  12 . Stated another way, the cylinder section  46  of the barrel extension can be incorporated into the proximal end  59  of the barrel and the collar of the barrel extension can be integrally formed with the external surface of the barrel  12 . 
     It therefore can be seen that the construction of the gas-operated firearm with a barrel mounting and retention device according to the principles of the present disclosure provides a firearm with an apparatus for affixing and retaining the barrel in a locked engagement with the receiver while further providing for substantially automatic indexing and aligning of the components of the barrel mounting and retention device with the receiver. Thus, the barrel mounting and retention device facilitates a user&#39;s easy-attachment and removal/replacement of the barrel to the receiver of a firearm, including firearms with integral or monolithic upper receivers having hand guards integrally attached or formed therewith. The present barrel mounting and retention system further enables replacement of the barrel without having to remove and/or replace the hand guard or other access device of the firearm. 
     The corresponding structures, materials, acts, and equivalents of all means plus function elements in any claims below are intended to include any structure, material, or acts for performing the function in combination with other claim elements as specifically claimed. 
     Those skilled in the art will appreciate that many modifications to the exemplary embodiments are possible without departing from the scope of the invention. In addition, it is possible to use some of the features of the embodiments described without the corresponding use of the other features. Accordingly, the foregoing description of the exemplary embodiments is provided for the purpose of illustrating the principle of the invention, and not in limitation thereof, since the scope of the invention is defined solely be the appended claims.