Patent Publication Number: US-10782082-B2

Title: Bolt assembly for blowback type firearms

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application No. 62/574,811 filed Oct. 20, 2017, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present invention generally relates to firearms, and more particularly to a bolt assembly which reduces felt recoil when discharging a firearm. 
     Some self-loading long guns (e.g. rifles and carbines) with ammunition magazines utilize a blowback type operating system or action. In such firearms, a non-locking and non-rotatable type bolt of one-piece construction is commonly used. Unlike rotating bolts used in manual bolt-action rifles or AR-15/M16 type rifles, blowback bolts form a closed but not a mechanically locked breech because they lack the radial bolt lugs and mating lugs formed in the receiver or barrel necessary to create a locked breech like the foregoing firearms. Instead, bolts used in blowback type operating systems rely on inertia created by the weight of the bolt and a forward spring-force applied to the bolt in order to maintain a closed breech during firing. 
     Bolts found in blowback type operating systems generally comprise a front breech block and face which abuts the rear of the cartridge chamber formed in the barrel to form the closed breech. After discharging the firearm, the bolt is thrust rearward by considerable recoil forces generated by detonating the gunpowder load in the cartridge. The bolt travels rearward to open the breech and unload the spent cartridge casing, and then is returned forward by a recoil spring to strip a fresh cartridge from the magazine which is chambered by the bolt. 
     The recoil forces generated by firing a blowback type firearm with one-piece bolt creates a peak recoil force that is felt by the user (“felt recoil”), which may be greater than desired. Accordingly, an improved bolt design is desired which lessens felt recoil. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide an improved bolt assembly for firearms utilizing a blowback type operating system. A multi-piece bolt assembly is provided in one embodiment comprising a bolt slideably disposed in the firearm receiver for forward and rearward movement and a dead blow weight assembly operably coupled to the bolt. The dead blow weight assembly is slideably mounted to the bolt and movable in a linear manner rearward and forward with respect to the bolt under recoil. The present bolt may be both non-rotatable and non-locking in design and operation. A recoil spring acts on the dead blow weight assembly, which in turn biases the bolt forward towards a closed breech position. 
     In one embodiment, the dead blow weight assembly may be two-piece comprising a dead blow weight and dead blow top member. These parts are separate components movable independently of each other, but functionally are interacting and cooperating under recoil after discharging the firearm to eject a spent cartridge casing and chamber a new cartridge as the action is reset. When the firearm discharged, a two-stage felt recoil force is generated by this mechanism, thereby advantageously producing peak forces which are less in magnitude than the single strong felt recoil force experienced by users with conventional one-piece bolt used in many blowback type firearms. 
     In one respect, a blowback type firearm with bolt assembly comprises: a longitudinal axis; a receiver defining a longitudinally-extending cavity; a barrel supported by the receiver; a bolt slideably mounted in the receiver for reciprocating movement between a forward closed breech position in battery with the barrel and a rearward open breech position; a dead blow weight assembly slideably mounted to the bolt, the dead blow weight assembly moveable relative to the bolt between a forward position and rearward position; and a return spring acting on the dead blow weight assembly, the return spring biasing the dead blow weight assembly towards the forward position, the dead blow weight assembly in turn acting on and biasing the bolt towards the closed breech position. In one embodiment, the 
     In another respect, a blowback type firearm with bolt assembly comprises: a longitudinal axis; a receiver housing a trigger-actuated firing mechanism and defining an axially elongated cavity; a barrel supported by the receiver; a bolt slideably mounted in the cavity of the receiver for reciprocating movement between a forward closed breech position in battery with the barrel and a rear open breech position; a dead blow weight assembly slideably mounted to the bolt, the dead blow weight assembly moveable relative to the bolt between a forward position and rearward position; the dead blow weight assembly comprising: a dead blow weight slideably mounted in a chamber of the bolt and movable forward and rearwards therein; and an axially elongated dead blow top member slideably positioned on top of the bolt and the dead blow weight, the dead blow top member axially movable forward and rearward relative to both the dead blow weight and bolt; and a return spring acting on the dead blow weight assembly, the return spring biasing the dead blow weight assembly towards the forward position, the dead blow weight assembly in turn acting on and biasing the bolt towards the closed breech position. 
     In another respect, a blowback type firearm with bolt assembly comprises: a longitudinal axis; a receiver defining an axially elongated cavity; a barrel supported by the receiver; a non-rotatable bolt slideably mounted in the cavity of the receiver for reciprocating movement between a forward closed breech position in battery with the barrel and a rear open breech position; a dead blow weight slideably disposed in an upwardly open chamber of the bolt, the dead blow weight moveable relative to the bolt between a forward position engaging a front surface in the chamber when the bolt is in the closed breech position, and a rearward position engaging a rear surface in the chamber when the bolt is in the open breech position; an axially elongated dead blow top member slideably positioned on top of the bolt and selectively engageable with the dead blow weight, the dead blow top member axially movable forward and rearward relative to both the dead blow weight and bolt; and a return spring acting on the dead blow top member, the return spring biasing the dead blow top member forwards which in turn biases the dead blow weight towards the forward position; the dead blow weight in turn biasing the bolt towards the closed breech position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the exemplary embodiments will be described with reference to the following drawings where like elements are labeled similarly, and in which: 
         FIGS. 1 and 2  are right and left side views of a firearm with blowback type operating system having a multi-piece bolt assembly according to the present disclosure; 
         FIG. 3  is a bottom plan view thereof; 
         FIG. 4  is a right side longitudinal cross-sectional view thereof; 
         FIG. 5  is an enlarged view of the breech area of the firearm taken from  FIG. 4 ; 
         FIGS. 6 and 7  are right and left perspective views of the bolt assembly of  FIG. 1  including a dead blow weight assembly; 
         FIG. 8  is a bottom front perspective view thereof; 
         FIG. 9  is an exploded view thereof; 
         FIGS. 10 and 11  are front and rear end views thereof; 
         FIGS. 12 and 13  are top and bottom plan views thereof; 
         FIG. 14  is a right side view thereof; 
         FIG. 15  is a longitudinal cross-sectional view of  FIG. 14 ; 
         FIG. 16  is a front perspective view of a replaceable and interchangeable cartridge seat insert of the firearm of  FIG. 1 ; 
         FIG. 17  is a rear perspective view thereof; 
         FIG. 18  is a top plan view thereof; 
         FIG. 19  is a right side view thereof; 
         FIG. 20  is a front end view thereof; 
         FIG. 21  is a top perspective view of a dead blow top member of the dead blow weight assembly of the bolt; 
         FIG. 22  is a bottom perspective view thereof; 
         FIG. 23  is a side view thereof; 
         FIG. 24  is a top view thereof; 
         FIG. 25  is a bottom view thereof; 
         FIG. 26  is a front end view thereof; 
         FIG. 27  is a rear end view thereof; 
         FIG. 28  is a right side view of the bolt body; 
         FIG. 29  is a front view thereof; 
         FIG. 30  is a left side view thereof; 
         FIG. 31  is rear view thereof; 
         FIG. 32  is top plan view thereof; 
         FIG. 33  is a bottom plan view thereof; 
         FIG. 34  is an exploded cross-sectional perspective view of the bolt and dead blow weight assemblies; 
         FIG. 35  is a first cross-sectional view of a sequential series of figures showing operation of the multi-piece blowback-type bolt assembly according to the present disclosure; 
         FIG. 36  is a second sequential view thereof; 
         FIG. 37  is a third sequential view thereof; 
         FIG. 38  is a fourth sequential view thereof; 
         FIG. 39  is a fifth sequential view thereof; 
         FIG. 40  is a sixth sequential view thereof; 
         FIG. 41  is a seventh sequential view thereof; 
         FIG. 42  is a eighth sequential view thereof; 
         FIG. 43  is a ninth sequential view thereof; 
         FIG. 44  is a tenth sequential view thereof; 
         FIG. 45  is a eleventh sequential view thereof; 
         FIG. 46  is a twelfth sequential view thereof; 
         FIG. 47  is a thirteenth sequential view thereof; 
         FIG. 48  is a fourteenth sequential view thereof; and 
         FIG. 49  is a fifteenth sequential view thereof; 
     
    
    
     All drawings are schematic and not necessarily to scale. Parts shown and/or given a reference numerical designation in one figure may be considered to be the same parts where they appear in other figures without a numerical designation for brevity unless specifically labeled with a different part number and described herein. Any references herein to a whole figure number (e.g.  FIG. 1 ) shall be construed to be a reference to all subpart figures in the group (e.g.  FIGS. 1A, 1B , etc.) unless otherwise indicated. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The features and benefits of the invention are illustrated and described herein by reference to preferred but non-limiting exemplary embodiments. This description of the embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. Accordingly, the invention expressly should not be limited to such embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto. 
     In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures may be secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. 
       FIGS. 1-5  depict a firearm  20  including a bolt assembly  50  according to the present disclosure. In one non-limiting embodiment, the firearm as illustrated may be a carbine. However, the firearm could be rifle with longer barrel. 
     Firearm  20  includes a longitudinal axis LA, receiver  21 , barrel  22  coupled thereto, bolt assembly  50 , and a trigger-actuated firing mechanism  23  supported by the receiver and including a movable trigger  24  mounted to the receiver. The firearm includes a rear buttstock  120  mounted to the receiver and forearm  121  mounted to the receiver and/or barrel. A downwardly open magazine well  32  is formed by the receiver which holds an ammunition magazine  33  (shown in dashed lines) detachably mounted in the well. Such magazines may hold a spring-biased vertical stack of ammunition cartridges C which are uploaded into the breech area  34  for loading into the rear of barrel  22  by the bolt assembly  50  in a conventional manner when cycling the action. In one embodiment, the cartridge C may be a centerfire cartridge with a centrally located percussion cap disposed in the rear exposed end of the base of the cartridge. This type of cartridge is well known to those skilled in the art without further elaboration. The magazine  33  is removably retained in the magazine well  32  by a pivotable magazine latch  35 . 
     Barrel  22  includes an axial bore  37  extending longitudinally and axially from a rear breech end  38  to a front muzzle end  39  from which a bullet or slug is discharged from the firearm. The centerline of bore  37  is coaxial with and defines the longitudinal axis LA of the firearm. The rear breech end  38  of the barrel  22  defines a rearwardly open diametrically enlarged chamber  36  configured for holding a cartridge C. 
     Receiver  21  defines an axially elongated internal cavity  40  which slidably carries and supports the bolt assembly  50 . Cavity  40  extends along the longitudinal axis LA between the open front end  18  in communication with the barrel chamber  36  for loading cartridges therein and a closed rear end  19  defined by vertical rear end wall  43 . Barrel  22  is coupled to the front end  18  of the receiver. In one non-limiting embodiment, the receiver  21  includes a right ejection port  44  and left ejection port  45  formed on opposite lateral sides of the receiver. 
     The firing mechanism  23  may further include the following components mounted in the receiver  21 : a pivotable and cockable hammer  25 ; pivotable sear  26  which is configured and operable to hold the hammer in a rear cocked position (see, e.g.  FIG. 3 ); a sear disconnector  27  operably engaged with the sear; and disconnector spring  27   a  acting between the disconnector and sear. Hammer  25  is biased forward by hammer spring  31 . Pulling the trigger  24  rearward operates to lift disconnector  27  which in turn rotates the sear  26 . This disengages a hook or ledge  28  formed on the front of the sear from a downward facing sear notch  29  on the hammer  25 , thereby releasing spring-biased hammer  25  forward which strikes the rear end of firing pin  30  slidably carried by the bolt assembly  50 . This drives the firing pin forward to strike a chambered cartridge C held in the chamber  36  of the barrel  22  for discharging the firearm  20 . 
     Bolt assembly  50  is axially movable in the internal cavity  40  of the receiver  21  between forward closed breech and rearward open breech positions. A bolt handle  51  is rigidly secured to the bolt  52  of the assembly to manually cycle the action and move the bolt between the forward and rearward positions. Bolt assembly  50  is also automatically moved under recoil between the forward and rearward positions when the action is cycled after discharging the firearm to eject a spent cartridge casing and chamber a new fresh cartridge. Cavity  40  therefore has an axial length to provide the full range of motion necessary for the bolt assembly  50  moving rearward under recoil to open the breech sufficiently for extracting and ejecting a spent cartridge casing, and uploading a new cartridge into the barrel chamber  36  from the magazine  33 . In one embodiment, without limitation, the bolt  52  may be part of a “blowback” type action firearm in which the bolt does not lock in place with the barrel chamber by using a rotating bolt or other type of mechanical toggle. Simple blow back designs are generally feasible for cartridges with low pressures, typically for example 0.22 LR, 9 mm, 0.45 ACP, and 0.40 S&amp;W. The main resistance which keeps the breach closed is achieved through the slide mass. 
     According to one aspect of the present disclosure, the bolt  52  and receiver  21  are constructed to provide an ambidextrous bolt handle  51  which allow the bolt handle to be mounted on either the right or left lateral side of the firearm to suit a right or left handed user. Referring to  FIGS. 1 and 2  showing the right and left sides of the firearm  20  respectively, the receiver  21  on both sides includes an axially elongated handle slot  119   a ,  119   b  through which bolt handle  51  protrudes when mounted in a corresponding bolt handle socket  118   a ,  118   b  formed on opposite lateral sides of the bolt  52  (see also  FIGS. 6 and 7 ). The bolt handle is shown mounted on the left side of the firearm  20  in the illustrated embodiment, but therefore can readily be positioned instead on the right side. Bolt handle  51  may be mounted to bolt  52  by any suitable means, including without limitation detachable mounting methods such as threaded engagement or pins to allow a user to switch the firing platform to left or right handed. In other implementations, for initial assembly of the firearm at the factory, the dual sided mounting options for the bolt handle may be used for fabricating and assembling a left or right handed firearm with the bolt handle being removably or permanently attached to the bolt on one side or the other. 
       FIGS. 6-15  depict various views of the bolt assembly  50  removed from the firearm. Bolt assembly  50  generally includes bolt  52 , extractor  54 , firing pin  30 , firing pin spring  55 , cartridge seat insert  56 , and a dead blow weight assembly  59 . 
       FIGS. 28-33  depicts various views of the body of the bolt  52  alone. Referring to  FIGS. 6-15 and 28-33 , bolt  52  has an axially elongated block-like body of generally rectilinear (e.g. rectangular cuboid) shape and includes front end  41 , rear end  42 , and right and left lateral sides  73 ,  74  extending between the ends. Bolt  52  defines an upwardly open upper chamber  65  extending for about half or a majority of the length of the bolt, and a downwardly and forwardly open lower chamber  66  of shorter length disposed proximate to front end  41  of the bolt. Lower chamber  66  provides open space and clearance for receiving the upper portion of magazine  33  when the magazine is fully mounted in the magazine well  32  (see also  FIG. 5 ). Upper chamber  65  is disposed between the front and rear ends  41 ,  42  of the bolt  52 , but may not penetrate the front and rear ends in some embodiments as illustrated. Upper chamber  65  includes a vertically deeper or taller rear section  65   a  and a vertically shallower or shorter front section  65   b  truncated at the bottom by horizontal partition wall  67  which extends axially forward from the rear portion. Partition wall  67  is spaced between the top and bottom  68 ,  69  of the bolt  52 , and slideably supports and engages the underside of the front portion of dead blow top member  58  for forward and rearward axial movement thereon. Dead blow weight  57  is inserted and slideably disposed in deeper rear section  65   a  of the upper chamber  65  when assembled to the bolt. The rear section  65   a  thus defines an upwardly open receptacle  210  which receives the dead blow weight  57 . Accordingly, the rear section  65   a  of upper chamber  65  has a complementary shape and dimensions in configuration to the dead blow weight. The dead blow weight  57  provides the “slide mass” for the blowback type action of the present firearm, as further described below. 
     The shallower front section  65   b  of the upper chamber  65  slideably receives the front portion of dead blow top member  58 . The rear portion of dead blow top member  58  is positioned in the upper part of the rear section  65   a  of upper chamber  65  above the dead blow weight  57 . The rear portion of the bolt bottom  69  may include a longitudinal hammer slot  206  (see, e.g.  FIGS. 8 and 13 ) which receives and slideably engages the hammer  27  during recoil to recock the hammer when the action is cycled after discharging the firearm. 
     Firing pin  30  is slideably disposed in a cylindrical axial bolt bore  64  in the bolt body which extends between the front and rear ends  41 ,  42  of the bolt  52 . In one embodiment, bolt bore  64  has a rear opening which opens through rear end  42  of bolt  52  and a front opening which opens through the front end  41  of the bolt (best shown in  FIG. 15 ). The rear end of the firing pin  30  protrudes beyond the rear end of the bolt through hole  313  for contact by the released hammer  25  when the trigger  24  is pulled to discharge the firearm. An intermediate portion of the firing pin  30  between the front and rear ends passes completely through the deeper rear section  65   a  of upper chamber  65  and receptacle  210 . The front opening of the bolt bore  64  is in communication with the through passage  97  formed in removable cartridge seat insert  56 . The front end of the firing pin  30  may be positioned within through passage  97  as illustrated. Firing pin spring  55  is also disposed in the bolt bore  64  and is arranged to engage annular flange  70  on firing pin  30  when thrust forward by a hammer strike on the rear end of the pin. This returns the pin rearward after discharging the firearm  20 . 
     The extractor  53  has a generally flat plate-like structure and includes a hooked front end  53   a , opposite rear end  53   b , and a pivot hole  71  disposed between the ends for receiving a first pull pin  62  (best shown in  FIG. 9 ). Pin  62  pivotably mounts the extractor to the bolt  52  in an axially extending horizontal slot  72  formed in the right lateral side  73  of the bolt. Pivot hole  71  and pull pin  62  may be disposed approximately midway between the front and rear ends of the extractor  53  in some embodiments. In one embodiment, slot  72  may extend partially rearward along the length of the bolt from the front end  41  towards the rear end  42  of the bolt body as illustrated. In this arrangement, slot  72  penetrates the front end of the bolt  52  as shown. 
     Pull pin  62  is received in a vertical hole pin  87  extending from and penetrating the top surface of the top  68  of the bolt  52  downward to and communicating with horizontal slot  72 . Hole  87  is positioned rearward from the the front of the slot  72  on the right lateral side  73  of bolt to access the pivot hole  71  in the extractor  53 . The bottom end of pin  62  is positioned in the slot  72 , and in some embodiments may extend below the slot in arrangements where hole  87  extends vertically below the slot in the bolt body. The bottom portion of pin  62  extends through hole  71  in the extractor  53  to pivotably mount the extractor to the bolt  52 . 
     Both the slot  72  and extractor  53  are horizontally aligned with the longitudinal axis LA and barrel bore  37  to place the hooked front end  53   a  of the extractor at approximately mid-height of a cartridge C when positioned in the barrel chamber  36  for extraction from the chamber. A laterally oriented extractor spring  86  mounted in the right lateral side  73  of the bolt  52  biases the rear end  53   b  of the extractor  53  outwards thereby rotating the front hooked end  53   a  inwards to engage the rim of the chambered cartridge C. Spring  86  in one non-limiting embodiment may be a coiled compression spring which is disposed in a laterally open spring hole  117   a  which intersects and is arranged perpendicular to the horizontal slot  72  in the bolt  52 . It will be appreciated that other types of springs or spring mechanisms may be used 
     Pull pins  60 - 62  in one embodiment include a lower cylindrical shank  99  and diametrically enlarged head  98  at the top of the shank. When the pull pins are fully inserted into the bolt  52 , the heads  98  of the pins abuttingly engage the top surface of the bolt when properly and fully mounted therein. This ensures that pins  60 - 62  have been inserted to a depth sufficient to secure the extractor  53 , ejector  54 , and cartridge seat insert  56  to the bolt assembly  50 . In addition, the enlarged heads  98  facilitates removal of the pins  60 - 62  via a tool having a flat working end (e.g. slotted fastener screw driver or other) which can be used to pry the pins upward for extractor from their respective vertical pin mounting holes. In some embodiments, the cartridge seat insert pull pin  61  may have a shank  99  with a cross-sectional shape other than cylindrical, as further explained elsewhere herein. 
     According to an aspect of the invention, cartridge seat insert  56  detachably mounts to the front end  41  of the bolt assembly  50  to allow the bolt  50  to accommodate and chamber a plurality of different types of cartridges via using a suitably configured seat insert. Advantageously, the removable cartridge seat allows for: 1) More flexible manufacturing by allowing caliber change through a less expensive insert rather than a complete bolt; 2) Reduces critical dimensions to the smaller less expensive component for matching a particular cartridge&#39;s dimensional requirements necessary to properly support the base of the cartridge and allow for its extraction during and after firing the firearm; and 3) Allows the end user an option to easily change calibers through the exchange of the relatively inexpensive replaceable component. 
       FIGS. 16-20  depict the replaceable cartridge seat insert  56  alone. The cartridge seat insert  56  can be considered to form a removable “bolt head” for engaging and forming a closed breech with the barrel (albeit a bolt head without any locking lugs typical for a blowback action). Referring now to the bolt assembly in  FIGS. 6-15  and the cartridge seat insert in  FIGS. 16-20 , cartridge seat insert  56  includes a front end  95 , rear end  96 , a laterally broadened front seating portion  90 , and part-cylindrical cantilevered rear extension  91  projecting rearwardly therefrom. Rear extension  91  is received and seated in a forwardly open socket  300  formed in the bolt  52  (see, e.g.  FIG. 15 ). An axial circular through passage  97  horizontally extends completely through the cartridge seat insert from the front end  95  to rear end  96  for slideably receiving the forward portion of firing pin  30  therethrough. The cartridge seat insert  56  is slideably insertably received in a forwardly open axial mounting receptacle  93  in bolt  52  and is coaxially aligned with the longitudinal axis LA of the firearm. Mounting receptacle  93  communicates with and is axially aligned with the circular axial firing pin bore  64  in the bolt  52  (see, e.g.  FIG. 15 ). 
     A pair of upwardly open vertical slots  94  are formed in stem  91  on each lateral side of cartridge seat insert  56  and receive second and third pull pins  60 ,  61  therethrough for removably locking the cartridge seat insert  56  in mounting receptacle  93  of the bolt  52 . Slots  94  are laterally spaced apart on opposite sides of the firing pin through passage  97  in cartridge seat insert  56 . Pull pins  60 ,  61  are received in vertical pin holes  88 ,  89  extending downwards through the bolt body from and penetrating the top surface of the top  68  of the bolt  52 . Vertical pin holes  88 ,  89  communicate with cartridge seat mounting receptacle  93  in the bolt body and slots  94  in the cartridge seat insert  56  when positioned therein. The bottom ends of pins  60 ,  61  are received in the slots  94  when fully inserted in pin holes  88 ,  89 . Holes  88 ,  89  are positioned near the front  41  of the bolt  52  and laterally offset from the longitudinal axis LA. Although the use of two laterally spaced apart pins  88 ,  89  provide stable mounting of the cartridge seat insert  56  in bolt  52  which resists twisting when the bolt recoils, it will be appreciated that in other embodiments a single pin and associated vertical slot may be used. 
     In one embodiment, slot  94  may be laterally open as well as upwardly open. The slot  94  may have a rectilinear or semi-circular cross-section (the illustrated embodiment showing the rectilinear configuration) which receives the cylindrical shanks  99  of pull pins  60 ,  61 . In other possible embodiments, the shank of the pull pin  61  may have a cross-sectional shape other than circular including non-circular shapes such as rectilinear, hexagonal, or other. Because the cartridge seat insert  56  does not rotate or pivot horizontally about the vertical pin axis of pull pins  60 ,  61  unlike the extractor  53  associated with cylindrical pull pin  62 , the shanks  99  of pins  60  and  61  do not require a circular cross-sectional to support rotational/pivotable motion. The cross-sectional shape of vertical slot  94  in some embodiments may therefore have a non-circular cross-sectional shape that complements the cross-sectional shape of shanks  99  of pull pins  60 ,  61 . 
     The front seating portion  90  has a lateral width substantially greater than the rear extension  91  and is seated in axial mounting receptacle  93  which defines a forwardly open frontal recess  92  formed in the front of the bolt  52 . The front recess  92  and mounting receptacle  93  may have a complementary configuration to seating portion  90  (see, e.g.  FIG. 6-10 ). This helps lock the cartridge seat insert  56  in position to preclude rotation about the longitudinal axis LA. With additional reference to  FIGS. 16-20 ), seating portion  90  includes a pair of an upper right wing segments  100  and lower right wing segment  102 . The upper wing segments are vertically spaced apart from the lower wing segments defining a right channel  104  therebetween. The channel  104  communicates with right horizontal slot  72  in the bolt  52  to receive the extractor  53  at least partially therein respectively. Accordingly, channel  104  is transversely aligned and falls in the same horizontal plane as the right horizontal slot  72 . In one non-limiting embodiment, as illustrated, the channel  104  may extend axially from the front to rear end of the front seating portion  90  of cartridge seat insert  56 . Cartridge seat insert  56  further includes a downwardly open undercut slot  303  configured to receive an ejector (not shown) which is mounted in the receiver of the firearm. Slot  303  is forwardly and rearwardly open as well to accommodate the ejector. 
     The front seating portion  90  may further include a downwardly extending polygonal-shaped key  112  which is received in a complementary configured keyway  111  formed in the axial mounting receptacle  93  of the bolt body (see also  FIG. 10 ). Key  112  may extend axially from rear end  96  to seating surface  106  of the cartridge seat insert  56 . This key further provides an anti-rotation feature to ensure that the cartridge seat insert  56  remains positioned in the proper rotational orientation when mounted to the bolt  52 . This feature helps to transversely align the axial channel  104  in cartridge seat insert  56  with the horizontal slot  72  in the bolt  52 , to provide smooth operation of the extractor  53  without binding. In one non-limiting embodiment, the right and left lateral sides  107 ,  108  of the cartridge seat insert  56  may generally be arcuately and convexly curved which mate with complementary configured concave surfaces in the cartridge seat insert mounting receptacle  93  of the bolt body. 
     The front vertical face of the seating portion  90  defines a vertical cartridge seating surface  106  (i.e. breech face) arranged to abuttingly engage the rear base end of the cartridge casing of cartridge C when the breech is closed (i.e. front of bolt  52  in battery with rear of barrel chamber  36 . Seating surface  106  is recessed in the front end  95  of the front seating portion  90  such that the lateral sides  107  and  108  including right upper and lower wing segments  100 ,  102  protrude longitudinal forward beyond the seating surface. This arrangement defines a forwardly open cartridge cavity  301  which receives the rear or base end portion of cartridge C therein. The through passage  97  of the cartridge seat insert  56  penetrates the cartridge seating surface  106  to allow the narrowed front end of the firing pin  30  to be projected outwards beyond the seating surface to strike the central percussion cap at the base of the cartridge C via a cocked hammer  27  released by a trigger pull. 
     The cartridge seating surface  106  and cartridge cavity  302  are configured and dimensioned to match the base diameter of a particular type and caliber of cartridge C received into the front recess of the front seating portion  90 . This ensures that the rear base end of the cartridge is properly supported during firing to prevent a cartridge casing rupture and provides positive extraction and ejection of the spend cartridge casing from receiver  21 . The lateral sides  107 ,  108  of cartridge seat insert  56  define opposing concave and arcuately curved lateral support surfaces  301  arranged in cartridge cavity  302  which also act to keep the cartridge C centered and to support the rear end of the cartridge during both feeding the cartridge into the chamber  36  before firing the firearm and extracting the cartridge rearward from the chamber after firing. Support surfaces  301  face inwards towards the longitudinal axis LA and through passage  97 . 
     In the present embodiment, the cartridge seat insert  56  may be removed and replaced by first dismounting the extractor  53 . To then remove the cartridge seat insert, with reference to  FIGS. 6-15 , pull pins  60 ,  61  are first removed from the bolt  52  by pulling vertically upwards to disengage the pin from the slots  94  in the cartridge seat insert  56 . The cartridge seat insert is then axially withdrawn forward and outwards from the frontal recess  92  in the front of the bolt  52  past the extractor. A new cartridge seat insert  56  is then axially reinserted rearward into the front recess  92  past the extractor after first axially aligning the channel  104  with extractor slot  72  in the bolt. The key  112  is inserted into keyway  111  in the bolt  52  until the vertical rear surface  115  of the front seating portion  90  abuts the mating front vertical surface  116  of the bolt  52  formed within the frontal recess  92  (see, e.g.  FIG. 15 ). This firmly seats the cartridge seat insert fully against the bolt and vertically aligns the slots  94  in the cartridge seat insert  56  with pin holes  88 ,  89  in the top of the bolt  52 . The pull pins  60 ,  61  are then reinserted through pin holes  88 ,  89  to engage the cartridge seat insert  56 , thereby locking the new cartridge seat insert  56  in place. It will be appreciated that the latter basic mounting process steps noted above may be used to initially install a new cartridge seat insert on the bolt in the first place. 
     Blowback Operating System 
     According to one aspect, embodiments of the present firearm may include a “blowback” type action. Appendix A attached hereto and forming part of the written description describes and illustrates operation of the blowback action. It bears noting that the bolt  52  in this blowback action functions to form a closed, but not necessarily “locked” breech in a conventional sense. This is due to the fact that the bolt  52  does not have rotatable radial bolt lugs which interlock with lugs formed at the rear of the barrel chamber such as in locked breech type firearms. Instead, blowback type actions rely on the weight or mass of the bolt and return spring force to maintain a closed breech. Bolt  52  may therefore be both non-locking and non-rotating in one embodiment. 
     Referring now to  FIGS. 5-15  and Appendix A, the blowback action includes dead blow weight assembly  59  comprising a dead blow weight  57  and dead blow top member  58  which cooperates with the dead blow weight to control cycling and timing of the action. Dead blow weight  57  is slideably received in upwardly open upper chamber  65  (i.e. rear portion  65   a ) of bolt  52  for forward and rearward movement therein with respect to the bolt. The dead blow weight provides the majority of “slide mass” of the dead blow weight assembly for the blowback type action. The dead blow top member  58  is slideably received in both the front and rear portions  65   a ,  65   b  of the bolt upper chamber  65 , as further described herein. 
     Dead blow top member  58  may have a substantially flat plate-like body including a top  219 , bottom  220 , front end  216 , rear end  217 , and pair of opposing lateral sides  218  extending axially between the ends (see also  FIGS. 21-27 ). Dead blow top member  58  have a substantially polygonal or rectilinear polygonal configuration. The body of the top member  58  may have a lateral width which is greater than the height or thickness of body. In one configuration, the dead blow top member has a length longer than a majority of the length of the bolt  52  and greater than rear section  65   a  of the upper chamber  65 . 
     The dead blow top member  58  is slideably mounted in the bolt  52  above the dead blow weight  57  which is movably disposed in rear section  65   a  of the bolt upper chamber  65 . Under recoil when the dead blow action is cycled, the dead blow top member  58  moves between a forward position and a rearward position relative to the bolt  52 . To guide movement of the dead blow top member  58 , the top member includes at least one outwardly and laterally projecting guide flange  304  disposed on each lateral side  218  of the dead blow top member body. In one embodiment, a pair of axially spaced apart guide flanges  304  may be formed on each lateral side of the dead blow top member. The guide flanges  304  are slideably received in mating longitudinally-extending guide channels  305  formed on the bolt (see, e.g.  FIGS. 9 and 11 ). The opposing guide channels  305  are inwardly open and may extend for a majority of the length of the bolt body. A guide channel  305  is disposed in right and left lateral sides  73 ,  74  of bolt  52  and communicate with the front and rear sections  65   a ,  65   b  of the upper chamber  65 . In one embodiment, the underside of the dead blow top member  58  may be vertically spaced apart from the top surface of the dead blow weight  57  providing a clearance therebetween such that the only direct and operable engagement between the dead blow top member and dead blow weight occurs at the downwardly extending engagement protrusions  213  at the rear end of the dead blow top member. 
     The dead blow weight  57  may have a generally block-like rectilinear body including a forward facing vertical front abutment surface  230 , a rearward facing vertical rear abutment surface  231 , pair of opposite lateral sides  306 , top surface  307 , and a bottom surface  308  which slides on the floor of the upper chamber rear section  65   a . The four corners  310  of the dead blow weight  57  formed between the lateral sides and front/rear abutment surfaces may be convexly rounded in one embodiment (best shown in  FIG. 9 ). These corners abuttingly engage corresponding concavely rounded corners  311  in rear section  65   a  of upper chamber  65  in the bolt  62  (see, e.g.  FIG. 32 ) when the dead blow weight reciprocates forward/rearward in the cavity as the action is cycled. This combination of arcuately curved engagement surfaces reduces stress concentration factors in these corner regions to minimize cyclical stress fractures for repeated cycling of the bolt assembly. A longitudinally-extending bore  309  extends completely through the dead blow weight  57  and slideably receives the rear portion of firing pin  30  therethrough. The forward portion of the firing pin is received in axial bolt bore  64  in the bolt body. 
     When mounted in the bolt  52 , the dead blow weight  57  is seated and positioned in open receptacle  210  of the bolt  52  formed by the deeper rear section  65   a  of the upper chamber  65 . With additional reference to  FIGS. 15 and 28-33 , receptacle  210  defines a vertical front abutment wall  211  positioned to engage front abutment surface  230  of dead blow weight  57  and opposing rear abutment wall  212  positioned to engage rear abutment surface  231  of the weight. In one embodiment, the axial length of the receptacle  210  measured between front and rear walls  211 ,  212  is larger than the axial length  221  of the dead blow weight  57  to allow axial forward/rearward reciprocating movement of the weight within in the receptacle during recoil of the bolt and dead blow weight assembly (compare, e.g. Appendix A, FIGS. I and J). This forms a gap G between the dead blow weight  57  and receptacle front/rear abutment walls  211 ,  212 , which may be present in front or behind the dead blow weight at various time when the bolt  52  is cycled, as further described herein. The upper chamber  65  has an axial length which may be longer than the length of the dead blow top member  58  to accommodate its reciprocating motion as well. 
     Dead blow weight  57  is biased and held forward in the bolt  52  by a return spring assembly which acts on the dead blow top member  58  that in turn acts on the dead blow weight. The return spring assembly generally includes axially oriented return spring  200  and spring rod  201 . In one embodiment, spring  200  may be helical compression spring; however, other types of springs may be used. Spring rod  201  may be cylindrical and axially elongated in the direction of the longitudinal axis LA. Rod  201  has a front end  222  which is slideably received through an axially oriented captive mounting bore  203  formed in dead blow member  58  proximate to its front end  216  (see, e.g.  FIGS. 21-22 ). In one embodiment, bore  203  is formed on an upwardly extending rod mounting protrusion  202  disposed proximate to front end  216 . Accordingly, spring  200  also indirectly biases bolt  52  forward because the spring force is applied through the dead blow weight assembly to the bolt, as further described herein. It bears noting that other locations of axial bore  203  and mounting protrusion  202 , however, are possible. 
     The rear end  223  of the spring rod  201  may be fixedly attached to rear end wall  43  of the receiver  21  inside cavity  40 , or alternatively to buffer pad  205  disposed on the end wall  43  inside receiver cavity  40  as illustrated (see, e.g.  FIGS. 5 and 9 ). Buffer pad  205  may include an axially oriented mounting hole  314 , which in one embodiment may be formed in an upright protrusion of the pad as shown, that receives the rear end  223  of spring rod  201  (see, e.g.  FIG. 9 ). Any suitable type of removable or permanent mechanical attachment feature  315  may be used to secure the spring rod  201  to the buffer pad  205 , for example without limitation clips, fasteners, welding, adhesives, friction fit, interference fit, interlock fits, etc. 
     The rear end of spring  200  acts on the rear of the receiver  21  or alternatively buffer pad  205 . The front end of spring  200  acts on the rod mounting protrusion  202  of the dead blow top member  58 . Advantageously, the location of the mounting protrusion  202  on the front of the dead blow top member  58  maximizes the length of spring  200  that can be used, which in turn maximizes the spring force that can be delivered to maintain a closed breech via interaction between the dead blow weight assembly  59  and bolt  52 . Return spring  200  has a horizontal line of action (i.e. parallel to longitudinal axis LA) imparted to the upright mounting protrusion  202  of the dead blow weight  57  which is vertically offset from and parallel to the longitudinal axis LA of the firearm (see, e.g.  FIG. 5 ). 
     The front end  222  of spring rod  201  may be diametrically enlarged relative to portions of the rod rearward from the front end including the rear end of the rod. This prevents the dead blow top member  58  from sliding off the front of rod when the bolt cycles rearward and forward in the receiver  21  after firing the firearm or manually cycling the action. The enlarged front end  222  thus may have a diameter larger than the axial bore  203  in the mounting protrusion  202  of the dead blow top member  58 . In one configuration, a longitudinally-extending concavity  204  may be formed in the top surface of dead blow top member  58  to partially receive the spring  200  and rod  201  therein. Concavity  204  extends axially for a majority of the length of dead blow top member  58  from mounting protrusion  202  rearwards to and penetrating rear end  217  of the top member in one embodiment. This advantageously contributes to the compactness of the design. 
     According to one aspect, the dead blow top member  58  is configured and operable to selectively engage dead blow weight  57  for moving the weight in upper chamber  65  of the bolt  52  when the bolt is cycled forward/rearward in recoil after discharging the firearm. Referring to  FIGS. 21-27 and 34  and also Appendix A, dead blow top member  58  includes at least one weight engagement protrusion  213  arranged to engage dead blow weight  57 . In one non-limiting embodiment, a pair of laterally spaced apart engagement protrusions  213  may be provided. Protrusions  213  extends downwardly from the bottom surface  220  of the dead blow top member. In one embodiment, the engagement protrusions  213  are preferably disposed at the rear end  217  of the dead blow top member  58 , and more preferably at the rear corners of the rear end to maximize the lateral spread of the protrusions. This positions the engagement protrusions  213  rearward of dead blow weight  57  to contact the two rear corner  310  regions of the dead blow weight. 
     Operation of the blowback operating system and bolt assembly will now be briefly summarized. The operation of the blowback system and reciprocating action of the bolt  52  and dead blow weight  57  is shown sequentially in  FIGS. 35-49  and described below. Note that directional arrows show movement/direction of the firing components. 
     Referring to  FIGS. 35-49 , when the bolt is in the forward ready-to-fire position with a closed breech ( FIG. 35 ), the return spring  200  urges the dead blow weight assembly  59  forward with respect to the bolt  52  to maintain breakable engagement of the dead blow weight  57  with the front abutment wall  211  in receptacle  210  of bolt  52 . The bolt head (cartridge seat insert  56 ) engages and holds the cartridge C in the chamber  36 . The spring-biased hammer  25  is cocked rearward and ready for release. 
     In  FIG. 36 , the trigger  24  is pulled to discharge the firearm. Pulling the trigger lifts the disconnector  27 , rotating the sear  26  downwards (clockwise). The sear releases hammer  25  which rotates forward (clockwise). The hammer drops and impacts the firing pin  30  ( FIG. 37 ) driving it linearly forward to strike the chambered cartridge C and ignite the primer. 
     After firing the firearm via actuating the trigger, the ignited cartridge pushes rearward on the bolt head, pushing the bolt  52  rearward. The bolt  52  carries the dead blow weight  57  linearly and axially rearward with it via the mutually engaged front abutment wall  211  and abutment surface  230  of the dead blow weight ( FIG. 38 ). The dead blow weight  57  in turn carries the dead blow top member  58  linearly reward with it via engagement between the rear engagement protrusions  213  on the top member with the rear abutment surface  231  of the dead blow weight. The rod mounting protrusion  202  on the dead blow top member  58  axially slides rearward along spring rod  201  (which remains stationary when the bolt is cycled rearward/forward) and compresses return spring  200 . During the process, the rearward travelling bolt  52  contacts and pushes/rotates the hammer  25  rearward and downward (counter-clockwise). The rotating hammer  25  makes first contact with the forward portion of the disconnector  27  to rotate it downwards (clockwise) as shown in  FIG. 39 . The rotating disconnector releases the sear  26 . The sear rotates upwards due to the disconnector spring  27   a  acting downwards on the rear end of the sear ( FIG. 40 ). During the process, the bolt assembly  50  and dead blow weight  59  continues traveling rearward in unison. 
     When the bolt  52  reaches its rearward-most position in the receiver  21  and abuttingly strikes the buffer plate  205  ( FIG. 41 ), the bolt rebounds forward off the buffer plate and the dead blow weight  57  slides and shifts axially rearward in receptacle  210  of the bolt  52  from its initial forward position to a rearward position. This breaks engagement between the front abutment surface  230  of the dead blow weight  57  and the front abutment wall  211  of the bolt  52  inside the receptacle. The rearward traveling rear abutment surface  231  of the weight abuttingly meets and contacts the rear abutment wall  212  of the receptacle ( FIG. 42 ) to temporarily hold the bolt assembly rearward momentarily against the forward biasing effect of spring  200 , thereby allowing time for a fresh cartridge to be uploaded into the action from the magazine before the bolt starts moving forward again. The forward motion of the bolt  52  is thus very briefly stopped or arrested. 
     The dead blow top member  58  continues to travel rearward independently of the bolt  52  and dead blow weight  57 . Engagement between downwardly depending protrusions  213  and the rear of the dead blow weight  57  is broken. The dead blow top member then makes contact with the buffer plate  205  ( FIG. 43 ). It bears noting that the dead blow weight  57  itself does not contact the buffer plate  205 . The dead blow top member  58  rebounds forward and re-engages the dead blow weight  57  via downwardly depending protrusions  213  ( FIG. 44 ). The dead blow weight and dead blow top member travel forward together in mutual engagement. This returns the dead blow weight  57  forward in receptacle  210  and re-engages front abutment surface  230  of the dead blow weight  57  with the front abutment wall  211  of the bolt  52  inside the receptacle ( FIG. 45 ). The engaged assembly of the dead blow weight, dead blow top member, and bolt move axially forward in unison under the forward biasing force of return spring  200  ( FIG. 46 ). The dead blow weight assembly  59 , dead blow top member  58 , and bolt  52  continue travelling forward until the breech is re-closed ( FIG. 47 ). 
     As the breech closes, a fresh cartridge is uploaded into the action and chambered. In the process, the underside of the bolt  52  disengages the hammer  25 , which is held rearward and cocked by sear  26  for the next shot. The bolt  52  is in battery with chamber  36  of the barrel again. The trigger  24  is released and starts to rotate forward ( FIG. 48 ). The disconnector  27  lowers with the trigger. As the disconnector lowers, the disconnector spring  27   a  applies a rotational force, trying to rotate the disconnector. Once the disconnector  27  lowers far enough, it rotates and “hooks” onto the sear  26  ( FIG. 49 ). The trigger can now be pulled again and the whole forgoing cycle repeats. 
     By using essentially a two piece bolt mechanism, a bolt  52  and a dead blow weight assembly  59  compressed against the bolt by spring  200  but movable relative to the bolt, the blowback mechanism acts as a one piece bolt for absorption of the cartridge energy, but delivers two smaller impacts of less magnitude to the rear of the receiver after discharging the firearm than a traditional one-piece bolt. The resultant effect of this advantageously is a lighter recoil force imparted to the shooter and a delayed rebound of the bolt. Delaying the bolt  52  from rebounding back forward into battery with the barrel allows a split second more time for a fresh cartridge in the magazine to pop up into a position forward of the bolt and be ready for the bolt to strip it away from the magazine as the bolt advances into battery (closed breech). The reduction in peak recoil force does not mean that there is a reduction in overall actual recoil energy produced by the firearm. Rather, the recoil sensed or felt by the shooter (“felt recoil”) is advantageously lessened. 
     While the foregoing description and drawings represent preferred or exemplary embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes as applicable described herein may be made without departing from the spirit of the invention. One skilled in the art will further appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims and equivalents thereof, and not limited to the foregoing description or embodiments. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.