Abstract:
A modular grenade launcher system includes an upper chassis and lower chassis secured on opposite sides of a barrel of a weapon, such as a firearm. The chassis removably receives any of a plurality of interchangeable modules, including grenade launcher assemblies having different calibers. A separate modular and removable firing mechanism is provided, wherein multiple grenade launcher barrel assemblies can share a common firing mechanism. An accessory rail module is also provided to replace the grenade launcher barrel assembly and firing mechanism.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of U.S. Provisional Application No. 62/085,967 filed Dec. 1, 2015. The aforementioned provisional application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present development relates to grenade launchers and, more particularly, to a modular grenade launcher system which provides quick attachment and removal from a firearm and one or more barrels interchangeable with one or more additional barrels and/or accessory rail sections. In a further aspect, the modular grenade launcher system herein may also be configured as a handheld, standalone grenade launcher. 
       SUMMARY 
       [0003]    In one aspect, a barrel-interchangeable weapon system for use in conjunction with a firearm includes a chassis capable of being attached to and detached from the firearm. The chassis is configured to removably attach a modular grenade launcher system. The modular grenade launcher system comprises at least one trigger assembly and at least one grenade launcher barrel assembly. The chassis includes an upper chassis portion and a lower chassis portion removably attachable to the upper chassis portion. The chassis is configured to circumscribe the barrel of the firearm. The upper chassis portion has at least one lower edge and the lower chassis portion has at least one upper edge engaging the at least one lower edge. A first fastener on a lower surface of the lower chassis portion is capable of being attached to and detached from the at least one grenade launcher barrel assembly. A second fastener on a lower surface of the lower chassis portion is capable of being attached to and detached from the at least one trigger assembly. 
         [0004]    In another aspect, a barrel-interchangeable weapon system includes a frame having a fore end portion and a buttstock portion and a chassis capable of being attached to and detached from the frame. The chassis is configured to removably attach a modular grenade launcher system. The modular grenade launcher system comprises at least one trigger assembly and at least one grenade launcher barrel assembly. The chassis includes an upper chassis portion and a lower chassis portion removably attachable to the upper chassis portion. The chassis is configured to circumscribe the fore end portion of the frame. The upper chassis portion has at least one lower edge and the lower chassis portion has at least one upper edge engaging the at least one lower edge. A first fastener on a lower surface of the lower chassis portion is capable of being attached to and detached from the at least one grenade launcher barrel assembly. A second fastener on a lower surface of the lower chassis portion is capable of being attached to and detached from the at least one trigger assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0005]    The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
           [0006]      FIG. 1  is an isometric view taken generally from the side and below of an exemplary grenade launcher system herein attached to an assault rifle and employing an interchangeable 40 mm grenade launcher barrel module. 
           [0007]      FIG. 2  is an isometric view of the grenade launcher system appearing in  FIG. 1 , taken generally from the side and above. 
           [0008]      FIG. 3  is an isometric view similar to the view appearing in  FIG. 1 , illustrating additional interchangeable components. 
           [0009]      FIG. 4  is an isometric view illustrating the additional interchangeable components appearing in  FIG. 3 , taken generally from above. 
           [0010]      FIG. 5  is an exploded view illustrating the manner of connecting the upper and lower chassis, firing mechanism, and interchangeable components. 
           [0011]      FIG. 6  illustrates an alternative embodiment employing a barrel-interchangeable weapon body including a fore end portion and a buttstock portion, the weapon body cooperating with a selected barrel assembly and trigger assembly to provide a standalone grenade launcher. 
           [0012]      FIG. 7  is an exploded view of the embodiment appearing in  FIG. 6 . 
           [0013]      FIG. 8  is an isometric view of the lower portion of the gun-mounted configuration, namely, the firing mechanism, the lower rail, and the 40 mm barrel. 
           [0014]      FIG. 9  is an isometric, partially exploded view of the 40 mm barrel. 
           [0015]      FIG. 10  is an isometric, exploded assembly view of the lower chassis. 
           [0016]      FIG. 11  is a partially exploded view illustrating the manner of interchangeably connecting a Picatinny rail section in place of the grenade launcher barrel. 
           [0017]      FIG. 12  is an exploded view of a pistol grip used in connection with the trigger assembly. 
           [0018]      FIG. 13  is an exploded view of the buttstock assembly herein. 
           [0019]      FIG. 14  is an exploded view of the firing mechanism. 
           [0020]      FIG. 15  is an isometric view of the hammer 
           [0021]      FIG. 16  is an end view of the hammer  840 . 
           [0022]      FIG. 17  is a side cross-sectional view of the hammer taken along the lines  17 - 17  appearing in  FIG. 16 . 
           [0023]      FIG. 18  illustrates the trigger and hammer assembly when the hammer is about to drop, i.e., wherein the trigger is about 90% depressed. 
           [0024]      FIG. 19  illustrates the trigger and hammer assembly after the hammer has dropped. 
           [0025]      FIGS. 20 and 21  illustrate pivoting the proximal end of the grenade launcher barrel in the left and right directions, respectively. 
           [0026]      FIG. 22  illustrates an exemplary grenade launcher system employing a grenade launcher barrel assembly having electronic fire mode controls. 
           [0027]      FIG. 23  illustrates an exemplary grenade launcher system herein employing a grenade launcher barrel assembly and used in conjunction with a ballistics computer or fire control system. 
           [0028]      FIG. 24A  is a fragmentary perspective view of an alternative embodiment grenade launcher system illustrating an alternative fastener for securing the chassis to the firearm appearing in exploded view. 
           [0029]      FIG. 24B  is a partially exploded, fragmentary perspective view of the alternative embodiment grenade launcher system appearing in  FIG. 24A . 
           [0030]      FIG. 24C  is a perspective view of the alternative embodiment grenade launcher system appearing in  FIGS. 24A and 24B . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Referring now to the drawings, a first exemplary embodiment exemplary grenade launcher system appears in  FIGS. 1 and 2 . The grenade launcher system includes an upper chassis  110  and a lower chassis  112  which are secured to each other about opposite sides of a barrel  122  of a firearm  120 . The present system may advantageously be employed with a Heckler &amp; Koch 416, although it will be recognized that the present system may be used with any standard assault rifle, including without limitation an M4, AR15, or M16 rifle or carbine or the like. A firing mechanism  114  and a grenade launcher barrel assembly  116  are secured to the lower chassis  112 . 
         [0032]    The upper chassis  110  may be configured as a replacement for an upper hand guard of the firearm  120 . The upper chassis  110  includes a pair of openings  118  on opposite lateral sides of the barrel  122 . Threaded bolts  124  pass through the openings  118  and engage aligned openings  126  formed in the lower chassis  112  in cooperation with the threaded block nuts  127  attached to the lower chassis with fasteners  129 . The upper chassis  110  includes an upper accessory rail  128 , which may be a Picatinny rail (MIL-STD-1913, STANAG-2324) or other tactical rail. In the illustrated embodiment, the upper chassis and the lower chassis are secured about the barrel  122 , e.g., via a clamping attachment to the barrel or a component adjacent the barrel, such as the receiver, barrel nut, or the like. Clearance may be provided between the barrel and the upper and lower chassis members for the gas block, gas tube, etc. 
         [0033]    As best seen in  FIGS. 3-5 , the lower chassis  112  is configured to interchangeably receive a plurality  320  of interchangeable components. In the illustrated embodiment, the interchangeable components include the grenade launcher barrel assembly  116 , which may be for example a 40 mm barrel and one or more alternative caliber barrel assemblies  142 , which may include for example a 25 mm airburst or smart grenade launcher barrel. In certain embodiments, an accessory rail plate  144  may also be provided for interchangeable attachment in place of the grenade launcher barrel assemblies  116 ,  142 . 
         [0034]    As best seen in  FIG. 9 , the barrel assembly  116  includes a barrel  132  and a mounting surface  134  on the upper surface of the barrel. A first dovetail channel  136  is formed in the surface  134  and receives a first complementary dovetail plate  138 . The first dovetail plate  138  is secured within the first dovetail channel  136  with threaded fasteners  140 . A second dovetail channel  146  is formed in the surface  134  and receives a second complementary dovetail plate  148 . The second dovetail plate  148  is secured within the second dovetail channel  146  with threaded fasteners  150 . 
         [0035]    A main boss  152  is secured to the first dovetail plate  138  with threaded fasteners  154 . The main boss  152  includes an annular channel  156 . A second boss  160  is secured to the first dovetail plate  138  with threaded fasteners  158 . A third boss  162  includes an upper flange  164  and is secured to the second dovetail plate  148  with threaded fasteners  166 . A hand guard  170  is secured to the lower side of the barrel  132  at a proximal end  172  thereof, opposite distal end  174 , with threaded fasteners  176 . 
         [0036]    The lower chassis  112  includes a main body  130 . An upper edge  133  of the main body engages a lower edge  135  of the upper chassis  110 . The upper edges  133  and the lower edges  135  may include complementary fastening means, such as complementary axially extending male and female dovetail connectors, complimentary axially tongue and groove connectors, and so forth. In the preferred embodiments, the upper chassis member slidably and removably receives the lower chassis member. In such embodiments, the axially extending tongue, rib, male dovetail member, or other like protrusion, may be formed on one of the upper and lower chassis members and the channel, groove, female dovetail channel, etc. may be formed on the other one of the upper and lower chassis members. It will be recognized that the tongue, rib, male dovetail component may extend continuously along the length of the respective chassis portion, or, may be segmented along its length. 
         [0037]    As best seen in  FIG. 10 , the lower chassis  112  includes a manually actuatable release lever  180  for removing the grenade launcher barrel  116  from the lower chassis  112 , e.g., for replacement with the alternative caliber barrel  142  or rail plate  144 . The release lever  180  includes a locking cylinder  182  slidably received within a complementary opening  184  in the lower chassis. A serrated plate  186  includes axially extending arms  188  slidably received within an axially extending channel  196  located at the distal end  194  of the lower chassis  112  on opposite transverse sides thereof. The cylinder  182  engages a notch  190  in one of the arms  188  to secure the plate  186  in position at the distal end  194  of the lower chassis  112 . Upward movement of the lever  180  brings a notch  192  in the cylinder  182  into alignment with the arm  188 , allowing sliding outward movement of the serrated plate  186 . Serrations  198  on the plate  186  assist the user in manually sliding the plate  186  outward to remove an attached one of the interchangeable components  320  from the lower chassis  112 . 
         [0038]    A spring  200  and a locking tooth  202  are disposed between the arms  188  within the channel  196  and are secured to the plate  186  via a pin  204 . A main boss receiver  206  is secured via fasteners  207  to the underside of the lower chassis  112  and includes a generally vertically extending opening  208  for receiving the main boss  152 . The tooth  202  passes through a horizontal opening  210  in the receiver  206  and normally engages the channel  156  in the main boss  152  of the barrel assembly  116  or  142  of the main boss  152   a  of the lower rail module  144 . 
         [0039]    The tooth  202  is urged by the spring  200 , to secure the distal end of an attached barrel assembly or other interchangeable component in place. When the user manually presses up on the lever  180  and manually retracts the serrated plate  186 , the tooth  202  disengages from the channel  156  to permit removal of the barrel assembly or other attached module from the lower chassis  112 . 
         [0040]    The proximal end  212  of the lower chassis  112  includes a dovetail or T-slot  214  receiving channel (see  FIG. 11 ) which slidably receives a complementary dovetail or T-shaped mounting shoe  216  (see  FIG. 14 ) on the firing mechanism  114 . A firing mechanism release button  218  includes a rod  220  having a stop member  222  (see  FIG. 11 ) extending into the receiving channel  214 . A captured spring assembly  224  resides within a notch or recess  225  formed in the rod  220  and biases the rod  220  such that the stop member  222  is positioned in the receiving channel  214  and blocks removal of the mounting shoe  216 , thereby securing the firing mechanism  114  in the proximal position. 
         [0041]    Manually pressing the button  218  against the urging of the spring assembly  224  moves the stop  222  out of the way to permit removal of the firing mechanism  114  by disengaging the mounting shoe  216  from the receiving channel  214 . When the firing mechanism release button is actuated by the user, the firing mechanism module  114  slides forward and drops out of the receiving channel  214 . The rod  220  is slidably retained within the lower chassis  112  via a cover plate  226  secured to the inner floor of the channel defined by the lower chassis  112  via threaded fasteners  228 , the cover plate  226  having a channel  230  formed therein receiving the rod  220 . 
         [0042]    A left/right lever  240  is manually pivotable to allow the rearward end  212  of the barrel assembly  116  to selectively pivot away from the firing mechanism  114  to either the left (see  FIG. 20 ) or the right (see  FIG. 21 ), as desired by the user, e.g., based on the handedness of the operator, for the purpose of chambering another round. The left/right lever is attached to a rod  244  that rotatably extends through an opening  246  in the lower chassis  112 . Protrusions  248  are provided on the exterior surface of the lower chassis  112  on opposite sides of the opening  246 . The protrusions act as stops to define the limits of rotation of the lever  240  and may carry indicia thereon such as “L” and “R” to indicate the side to which the barrel  116  will swing open when the sliders  290  are actuated, as detailed below. 
         [0043]    A cam member  250  is coaxially received on the rod  244  and is secured thereto by a pin  252  passing through aligned openings  254  and  256  in the cam member  250  and rod  244 , respectively. A torsion spring  260  is received about a pin  262 , which in turn, is received through an opening  264 , which is adjacent the opening  246 . The torsion spring  260  bears against a cam surface  266  on the cam member  250  to provide an over center function to secure the lever in either the fully pivoted left or right position and to resist inadvertent pivoting of the lever  240 . 
         [0044]    The outward ends of the cam member  250  include partial flanges  270   a  and  270   b.  The partial flanges are angularly displaced so that one of the flanges  270   a  and  270   b  is moved into an opening  272  (see  FIG. 11 ) in the base of the lower chassis  112  when the lever  240  is pivoted to the “left” position and the other one of the flanges  270   a  and  270   b  is moved into the opening  272  when the lever  240  is pivoted to the “right” position. The flanges  270   a  and  270   b  selectively block movement of a protrusion  280  (see 
         [0045]      FIG. 9 ) on the bottom of the barrel  116  in a channel in the respective direction to permit pivoting movement of the barrel  116  about the main boss  152  in one direction only. An arcuate or angled T-slot  282  having a profile which is complementary with the boss  162  and flange  164  is provided in the lower surface of the lower chassis  112  to allow the barrel  116  to pivot in the selected direction, e.g., as shown in  FIGS. 20 and 21 . 
         [0046]    Pivoting movement of the barrel is actuated by manually sliding a pair of sliders  290  which are disposed on opposite transverse sides of the lower chassis  112 . Each slider  290  is attached to a respective shoulder  294  of a sliding cam  292  via a fastener  291 . The sliding cam  292  is secured within the interior of the lower chassis  112  by a plate  296  and is constrained to reciprocal movement in the axial direction. 
         [0047]    The sliding cam  292  includes a central opening  300 , which is aligned with a central opening  302  in the plate  296 . An engaging member  310  engages the sliding cam  292  and extends through the openings  300  and  302  and engages an opening  168  in the dovetail plate  148  (see  FIG. 9 ) to prevent pivoting movement of the barrel  116  relative to the lower chassis  112 . To pivot the barrel  116  to an open position, the sliders  290  are manually slid in the forward axial direction by the user. Movement of the sliders causes the sliding cam  292  to move forward. The sliding cam has inclined ramp surfaces  304  that engage complementary inclined features  312  on the engaging member  310 . Forward sliding movement of the sliding cam  292  in the axial direction causes upward movement of the engaging member  310  to withdraw the engaging member  310  from the opening  168  and to allow the barrel  116  to pivot in the user-selected direction about the main boss  152 . 
         [0048]    A spring assisted opening mechanism for opening the barrel includes a spring  328  encapsulated in a case  324  and retained by a pin  316 . The spring  328  pushes on a first cam  338 , which slides against a second cam  348 . The cam  348  is secured to a sliding carriage  356  via screws  377 . The sliding carriage is connected to two paddles  358  via screws  376 , which come into contact with the second boss of lug  160  on the barrel (see  FIG. 9 ) to transfer the energy used to open the barrel. The transverse distance between the paddles  358  is larger than the thickness of the lug  160  to provide a small amount of play in the system which, in turn, causes the barrel to be actuated in the direction in which it was last opened. 
         [0049]    The interchangeable, alternative caliber barrel assembly  142  includes a hand guard  170   a  and a barrel  132   a.  In certain embodiments, the barrel assembly  142  may include an electronic fire mode control system  143 , e.g., of a type which may be used to program or select a firing mode of a programmable grenade or other munition round. For example, the fire mode control system may be used to program the munition round for air burst mode or impact detonation. In certain embodiments, the electronic fire mode control system  143  may be used to input a desired detonation distance to a grenade in the firing chamber. In certain embodiments, the distance traveled is tracked by determining the number of spiral rotations the grenade undergoes after it is fired. The present system may be used in conjunction with a range finder, such as an optical range finder, and the electronic fire mode control system  143  is used for inputting determining the distance to the target. In certain embodiments, the barrel assembly may be compatible with the XM25 grenade launcher platform. 
         [0050]    As shown, for example, in  FIG. 4 , the alternative barrel assemblies such as the barrel assembly  142  will have a like mounting surface  134  and similar retention and pivot components thereon, which may be as described above in connection with the barrel assembly  116 . The lower accessory rail module  144  replaces the barrel assembly  116  or  142  and the firing mechanism  114  and does not pivot. The upper (in the orientation shown) surface of the lower rail module  144  includes a main boss  152   a  secured to a dovetail  138   a  received within a complimentary dovetail channel  146   a  formed in the rail member  144 . The main boss  152   a  is removably received with the main boss receiver  206  of the lower chassis as described above to removably secure the forward end of the rail member  144  to the lower chassis. The lower rail member  144  further includes and a dovetail or T-shaped mounting shoe  216   a  on the upper surface thereof, which is slidably received in the receiving channel  214  to removably secure the rearward end of the rail member  144  to the lower chassis. 
         [0051]    With reference now to  FIGS. 6, 7, 12, and 13 , there appears a further embodiment wherein the modular grenade launcher system herein may be configured for use as a standalone weapon, i.e., without an associated firearm. The standalone configuration includes a frame comprising a fore end portion and a buttstock portion. The illustrated preferred embodiment depicts a preferred embodiment wherein the fore end portion and the buttstock portion are hingedly coupled, which allows the unit to be folded for storage and transport. It will be recognized, however, that nonfolding frames are also contemplated, e.g., wherein the buttstock portion and the fore end portion form an integral or unitary structure or are rigidly or non-foldingly attached to each other. 
         [0052]    In the depicted embodiment, an upper chassis  110   a  s coupled to fore end assembly  330  via a guiding member  332  and fasteners  334 . A proximal end of the fore end assembly  330  includes a hinge assembly  340 . The hinge assembly  340  includes a hinge body  342  pivotally attached to a pivot plate  344  via a hinge pin  346 . A lower chassis  112  is attached to the upper chassis  110   a  via fasteners  124 . The lower chassis  112  and the barrel assembly pivot and release features may be as described above. 
         [0053]    The fore end assembly  330  includes a pair of rods  350  extending from the distal end  343  of the hinge body  342 . The rods  350  pass through openings  352  in fasteners  336 . The fasteners  336 , in turn, are secured to the upper chassis  110   a  via threaded fasteners  354 . An end cap  360  is secured to the end of the upper chassis  110   a  via fasteners  362 . A half sleeve  364  is received about a shallow annular channel  366  in each of the rods  350  and is secured in place with a pin  368  passing through aligned openings in the corresponding rods and sleeves. The half sleeve members  364  protrude from the respective channel  366  and abut one of the fasteners  336  to provide a rigid connection and prevent relative axial movement between the upper chassis  110   a  and the fore end assembly  330 , e.g., as a result of recoil when a round is fired from an attached grenade launcher barrel  116  or  142 . 
         [0054]    The guiding member  332  includes first and second setscrews  380  rotatably received within threaded openings  382  on opposite transverse sides of the member  332 . 
         [0055]    Bearing members  384  are positioned between each of the setscrews  380  and a respective side surface  386  of the hinge body  342 . The guiding member  332  also includes a third setscrew  390  rotatably received within a threaded opening  392  in the clamp  332 . A bearing member  394  is positioned between the setscrew  390  and a lower surface  396  of the hinge body  342 . The setscrews  380 ,  390  can be advanced or retracted as necessary to adjust for any play in the gap between the guiding member  332  and the respective adjacent surfaces  386 ,  396  of the hinge body  342 . 
         [0056]    A buttstock assembly  370  includes an end plate  372  which is attached to the pivot plate  344  with fasteners  374 . The hinge assembly  340  includes a latch assembly for securing in the operable or unfolded position and releasing the hinge assembly for folding the buttstock relative to the fore end assembly. The latch assembly includes a push button  410  which is biased upward by a spring  412 . A latch member  420  is pivotally attached to the hinge body  342  on a side opposite the hinge pin  346  via a pin  422  to secure the hinge in the closed position. The hinge pin  346  passes through a channel  430  defined by interfitted knuckles on the hinge body  342  and the plate  344 . 
         [0057]    The hinge pin includes an upper head or flange portion  440 . The lower end of the hinge pin  346  includes a slot  432  extending in the direction of the pivot axis. A spacer  434  is received at the lower end and a lower head or flange member  450  is secured to the pin  346  and spacer  434  with a pin  436  flush with the lower end of the hinge pin  346 . The length of the spacer  434  is less than the length of the slot to define an opening  460  in the hinge pin  346 . Notches  462  and  464  in the knuckle portions of the hinge body and hinge plate cooperate to define an opening that is aligned with the opening  460  when the hinge is in the closed position. 
         [0058]    A lever  500  is captured within an opening  510  in the hinge body  342  and is pivotally rotatable about a threaded fastener  512 . The lever  500  is secured by a cover plate  514  via fasteners  516 . The lever includes a projection  520  that is received within the opening  460  and the opening defined by the notches or cutaway portions  462  and  464  to prevent pivoting of the buttstock  370  relative to the fore end assembly  330 . In operation, to fold the buttstock assembly  370  relative to the fore end assembly  330 , the release button  410  is manually depressed against the urging of the spring  412 . The lower end of the button  410  bears against a projection  415  on the lever  500  to move the projection  520  out of the opening defined by  460 ,  462 ,  464  to permit folding of the hinge assembly. 
         [0059]    As best seen in  FIG. 12 , a handgrip assembly  600  includes a handgrip member  610  and a fastener assembly  620  for removably securing the handgrip assembly  600  to the firing mechanism  114 . The handgrip  610  may be a commercially available handgrip. The fastener assembly  620  includes a housing  622  and a pivoting latching member  624  pivotally secured in the housing  622  with a pin  626 . The latching member  624  includes a tooth  628  that removably engages a complementary receptacle  630  (see  FIG. 7 ) on the firing mechanism and a lever  632 . A captured spring  634  within the housing  622  urges the tooth  628  into engagement with the receptacle  630 . A button  636  extends through an aligned opening in the housing and bears against the lever  632 . Manually depressing the button  636  pivots the lever  632  to compress the spring  634  and disengages the tooth  628  from the receptacle  630  to release the handgrip assembly  600  from the firing mechanism  114 . 
         [0060]    A side accessory rail assembly  700  includes a side rail section  710  secured to a sidewall  130  of the lower chassis  112  via threaded fasteners  712  and nuts  714 . The rail section  710  may be a Picatinny rail section or the like and may be used to mount an accessory device such as a ballistics computer or fire control system  730 , as shown in  FIG. 23 , or other accessory, such as a sighting device, range finder, laser designator, illuminator, camera, or the like. 
         [0061]    Referring now to  FIG. 14 , the firing mechanism  114  includes a housing  810  having a T-channel  812  formed at the bottom thereof for slidably receiving a complementary trigger guard  816  secured within the channel  812  via pins  820 . The trigger  824  extends through an opening  832  in the trigger guard  816  and is pivotal about a pin  836 . 
         [0062]    The trigger  824  is coupled to a sear  838  releasably engaging a hammer  840 . The sear  838  includes a curved or hooked distal end  839  which engages an indent or cavity  841  in the hammer  840 . The hammer is pivotally mounted within the housing  810  on a slotted pin  844 , which is retained within the A hammer spring  850  is received on the pin  844  which is retained in position in openings  852  in a firing mechanism cover  910  by clips  846 . 
         [0063]    As the trigger  824  is depressed, it simultaneously pulls down on the sear  838  and trigger linkages  848  on opposite transverse sides thereof and held together via linkage pin  849 . The sear  838  retracts the hammer  840  and compresses the spring  850  by pulling on the indent  841  until the sear point falls off the edge of the hammer indent  841 , at which point the trigger is released and powered forward by the hammer spring  850 . 
         [0064]      FIG. 15  is an isometric view of the hammer  840 .  FIG. 16  is an end view of the hammer  840 .  FIG. 17  is a side cross-sectional view of the hammer  840  taken along the lines  17 - 17  appearing in  FIG. 16 .  FIG. 18  illustrates the trigger and hammer assembly when the hammer is about to drop, i.e., wherein the trigger is about 90% depressed.  FIG. 19  illustrates the trigger and hammer assembly after the hammer has dropped. 
         [0065]    Each trigger linkage  848  is pivotally coupled to a connecting linkage  854 , which, in turn, transfers movement via a slide linkage  856  and a flipper slide  858  to a hammer disconnect plate  860 . The hammer disconnect plate  860  is a flipper that transfers energy to from the hammer  840  to a firing pin  862 , which extends through an opening in a firing pin retainer  872  in a firing pin housing  870 . The firing pin housing is secured to the front surface of the housing  810  via fasteners  874 . 
         [0066]    A trigger return spring  864  is received on the pin  836 , which is retained by clips  866 . When the trigger  824  is released, the trigger return spring  864  returns the trigger  824  to the forward position. The flipper  860  the lowers to provide a gap between the hammer  840  and the firing pin  862 , which in turn, allows the firing pin  862  to retract via the rearward urging of a firing pin return spring  868 . A sear return spring  880  is received on a linkage pin  882  and returns the sear  838  to the hammer indent  841 . 
         [0067]    A manual safety mechanism is also provided to prevent accidental discharge of the weapon and includes a safety catch  890  having a transverse rod portion  892  extending through openings in the housing  810 . Levers  894  are provided to manually rotate the safety between a safe position and a firing position. Indicia  896  are provided on the housing  810  to allow the user to visually determine whether the safety is on or off. 
         [0068]    The rod portion  892  includes a slot  898  which allows the hammer to retract therethrough when the safety lever is pivoted to the forward position. Pivoting the rod  892  to the upward or safe position moves the rod into the path of the hammer so that the hammer is unable to retract, thereby preventing discharge of the weapon. Safety detent springs  900  are received about a spring pin  902 . The springs  900  are torsion springs a having a forward leg  904  which is received within a corresponding and aligned detent or slot  906 . The legs  904  bear against the respective slot  906  to hold the safety mechanism in position. 
         [0069]    The firing mechanism cover  910  is secured to the top of the housing  810  via fasteners  912 . The cover plate includes the dovetail shoe  216  that is slidably received within the receiving channel  214  in the lower chassis  112 . 
         [0070]    Referring now to  FIGS. 24A-24C , there appears an alternative embodiment of the grenade launcher system which employs an alternative fastener for attaching the chassis to the firearm and a preferred dovetail configuration for securing the upper and lower chassis members. The embodiment appearing in  FIGS. 24A-24C  includes an upper chassis member  110   a  engaging a lower chassis  112   a.  The upper chassis  110   a  includes lower edges on opposite transverse sides having a plurality of axially extending tongues  137   a  and  137   b.  The lower chassis  112   a  includes lower edges on opposite transverse sides having a plurality of axially extending grooves  139   a  and  139   b  which are complimentary with the tongues  137   a  and  137   b,  respectively. 
         [0071]    The lower chassis  112   a  includes a distal end  113  having opposing, axially extending arms  115 . The distal end  113  includes an expansion joint defined by the arms  115  and a central expansion member  117  therebetween. The expansion member has a generally “I” shaped cross-sectional shape and includes upper and lower horizontal, axial flanges  119  and a vertical, axial web  121  extending therebetween, thereby defining channels  123  between the flanges  119 . The arms  115  each include and axial tongue  125  extending into a respective one of the channels  123 . The tongues  125  and channels  123 ,  123  are dimensioned to define clearance or gaps  131  to allow a degree of movement between the arms  115 . 
         [0072]    The fastener includes a drawbar  141  having a first, threaded end  145  rotatably engaging a tapped opening or boss  109  of a clamping member  111  in the lower chassis portion  112   a.  The drawbar  141  passes through openings in the sidewalls of the lower chassis  112   a  and also includes a second end  147  opposite the first end. A lever arm  149  is pivotally attached to the second end  147  via a hinge or pivot pin  151 . The pivot pin  151  passes through an opening  153  whereby the proximal end  155  of the lever arm  149  defines one or more cam surfaces  157 . 
         [0073]    The cam surfaces  157  are eccentrically shaped, e.g., wherein the cam surfaces  157  have a radius of curvature wherein the opening  153  is positioned off center with respect to the radius of curvature. The lever arm  149  is pivotable between a locked position as shown in  FIGS. 24A and 24C  and an unlocked position as shown in  FIG. 24B . In the locked position, the distance between the pivot pin  151  and the cam surfaces  157  is increased to thereby draw the clamping member  111  inward. A tooth or protrusion  159  passes through an opening  169  on the lower chassis portion  112   a  and is moved into engagement with a like depression or channel on the barrel nut on the firearm when the lever arm is moved to the locked position to exert a clamping force on the barrel nut of the firearm. Clamping pressure between the clamping member  111  and the cam surfaces  157  may also cause the arms  115  to move toward each other to close the clearance or gap  131 , thereby increasing the clamping force of the lower chassis member  112   a  on the firearm. Pivoting the lever arm  149  to the unlocked position causes the distance between the pivot pin  151  and the cam surfaces  157  to decrease, to allow the clamping member  111  to move away and release the clamping force on the barrel nut of the firearm. 
         [0074]    Movement of the lever arm  149  to the unlocked position also allows the user to rotate the drawbar with respect to the tapped opening  109  in the lower chassis member  112   a.  Rotation of the drawbar  141  with respect to the tapped opening  109 , in turn, allows the user to adjust the clamping force exerted when the lever arm is subsequently moved to the locked position. A threaded fastener  107  having an enlarged head engages the threaded end  145  through an opening  105  in the lower chassis portion  112   a  to prevent the drawbar  141  from completely disengaging with from the clamping member  111 . 
         [0075]    The clamping member  111  is carried on one or more pins  163  extending transversely between the opposing arms  115 . The pins carry biasing springs  165  thereon for urging the clamping member  111  outward and out of registration with the barrel nut to facilitate removal of the chassis from the firearm when the lever arm  149  is moved to the unlocked position. The arms  115  are movable in the transverse direction with respect to the pins  163 . 
         [0076]    In certain embodiments, the lever arm  149  may optionally include a locking tab  161  on the distal end thereof. The locking tab  161  is movable with respect to the lever arm  149  and may be biased (e.g., via a captured internal spring or other resilient biasing member, not shown) to engage a complimentary feature  171  on the lower shell  112   a.  In such embodiments, the user must manually disengage the tab  161  from the complimentary feature  171 , against the bias of the biasing member, in order to move the lever arm  149  from the locked position to the unlocked position. In this manner, inadvertent movement of the lever arm  149  from the locked position to the unlocked position can be avoided or minimized. 
         [0077]    The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.