Patent Description:
An example of a stock coupling system for a firearm is disclosed in <CIT>.

The rear stock (or buttstock) in a long gun generally attaches to the rear portion of the forward main body of the firearm formed by the forend stock or chassis which supports the receiver. The rear stock is used for shouldering the firearm when sighting the target down range before and during firing. Various techniques may be used to interface and mount the rear stock to the chassis. Some rear stocks are fixed in position inline with the firearm, while others allow folding the rear stock to facilitate carrying and storage of the firearm. In addition, many users have personal preferences on the style and configuration of rear stocks or buttstocks that they favor.

An improved stock coupling system is desired which is compatible for use with various different aftermarket rear stock configurations to suit personal user preferences.

The present disclosure provides an improved folding stock coupling system for detachably mounting the rear stock or buttstock to a forward main body of the firearm, which comprises the forend stock or chassis which in turn directly or indirectly supports the receiver of the firearm. The stock coupling system in one embodiment includes a universal rear stock mounting interface configured to accept a variety of different aftermarket rear stocks, and a detachable main body mounting interface. Such rear stocks for example may be AR-<NUM> type rifle stocks in some embodiments, which are mounted to a standard buffer tube of these type firearms. The present stock coupling system advantageously allows the user to select both their rear stock and firearm of choice, and readily interchange stocks with different firearms. The stock coupling system employs minimal moving components thereby providing a mechanically simple and reliable foldable stock coupling system.

The stock coupling system in one embodiment includes a button-actuated locking hinge mechanism or assembly configured and operable to allow the stock to be changed between an open unfolded inline position relative to the main body and longitudinal axis of the firearm for firing, and a closed folded offset position for storage/carrying. The hinge mechanism is configured to selectively lock the stock in the unfolded position as well as automatically retain the stock in the folded position along side the firearm main body via a detent mechanism, as further described herein. The detent mechanism allows the rear stock to be rapidly unfolded and returned to the inline position for firing without manually unlatching any components separately. The hinge mechanism automatically re-locks into the inline position without manually actuating the actuating button.

The hinge mechanism may be detachably coupled to the main body of the firearm by a clamping mechanism in certain embodiments. In one configuration, the clamping mechanism may be configured for mounting to a section/segment of a wedge-shaped Picatinny rail located at the rear of the main body. The Picatinny rail, well known in the art without further elaboration, is one stock mounting interface provision encountered in some firearms. Other mounting interface configurations and systems however may be used including simply threaded fasteners.

The present stock coupling system is usable with any type of long gun such as without limitation a rifle or shotgun, or any other type of long-format military/law enforcement or civilian small arms weapon which utilizes a rear stock and could benefit from a folding stock design according to the present disclosure.

According to the invention, a stock coupling system having the features of claim <NUM> is provided.

According to another aspect not forming part of the present invention, a firearm with interchangeable stock coupling system comprises: a main body comprising a longitudinal axis; a hinge mechanism comprising a front hinge member fixedly coupled to the main body, and a rear hinge member pivotably coupled to front hinge member; the hinge mechanism selectively movable between a locked condition in which the rear hinge member is not movable relative to the front hinge member, and an unlocked condition in which the rear hinge member is movable relative to the front hinge member; an elongated rear mounting extension projecting rearward from the rear hinge member; a first stock slideably coupled to the rear mounting extension, the stock slideable between a plurality of axial positions on the rear mounting extension for adjusting a length of pull of the firearm; and an actuating button movably mounted to the hinge mechanism, the actuating button being configured to lock the rear hinge member to the front hinge member in the locked condition of the hinge mechanism; wherein the first stock is movable between an unfolded position in which the first stock is inline with the longitudinal axis when the hinge mechanism is in the locked condition, and a folded position in which the first stock is laterally offset from the longitudinal axis when the hinge mechanism is in the unlocked condition.

According to another aspect not forming part of the present invention, a method for operating a stock coupling system of a firearm comprises: providing a firearm having a rear stock locked in an unfolded position inline with a longitudinal axis of the firearm; depressing an actuating button of a hinge mechanism having front and rear hinge members removably locked together; disengaging a pair of first locking protrusions on the actuating button from a pair of corresponding second locking protrusions on the front hinge member to unlock the hinge mechanism; rotating the rear stock about a pivot axis defined by the hinge mechanism; and placing the rear stock in a folded position laterally offset from the longitudinal axis of the firearm.

The features of the exemplary embodiments will be described with reference to the following drawings where like elements are labeled similarly, and in which:.

All drawings are schematic and not necessarily to scale. Parts 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/or described herein. Parts described herein with respect to certain figures may also appear in other figures in which they may be numbered or unnumbered unless otherwise noted herein. Furthermore, a general reference to a whole figure number which may include multiple alphabetic subparts shall be construed as a reference to all of the subparts unless specifically noted otherwise.

The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments.

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.

The term "action" which may be mentioned is used herein in its conventional sense in the firearm art as meaning the mechanism that loads and ejects shells into/from the firearm and opens and closes the breech (i.e., the area in the receiver between an openable/closeable breech face on the front of the bolt and the rear face of the barrel chamber).

As used throughout, any ranges disclosed herein are used as shorthand for describing each and every value that is within the range.

Referring initially to <FIG>, a firearm <NUM> in the form of a rifle in one embodiment is shown including a folding stock coupling system according to the present disclosure. Firearm <NUM> may be any type of long gun or small arms weapon (e.g., grenade launchers, etc.) including without limitation a rifle or a shotgun. In the non-limiting example illustrated, the firearm <NUM> may be an auto-loading rifle. The stock coupling system is not limited in its applicability to any particular long gun or weapon, however.

Firearm <NUM> generally includes a main body <NUM> which in the non-limiting illustrated embodiment comprises a forend stock or chassis 27a, receiver <NUM>, a trigger actuated fire control mechanism <NUM> mounted in the chassis and operable to discharge the firearm, a barrel <NUM> supported by the receiver, optionally a handguard <NUM> enclosing and circumscribing at least part of the length of the barrel, and folding stock <NUM>. Handguard <NUM> may similarly be coupled to a front end of the receiver and/or other portions of the firearm. The main body <NUM> of firearm <NUM> supports the receiver and fire control mechanism in one embodiment. Firearm <NUM> defines a right lateral side 20a and left lateral side 20b when viewed from the perspective of a user normally aiming the firearm downfield.

Barrel <NUM> has an elongated body including an open front muzzle end 23a and opposite open rear breech end 23b coupled to a front end of the receiver <NUM> in any suitable manner. Barrel bore 23d extends axially between the muzzle and breach ends and defines a projectile pathway. Diametrically enlarged cartridge chamber 23c is defined at rear breech end 23b and configured for chambering a cartridge for firing in a known manner.

The firearm <NUM> defines a longitudinal axis LA and axial direction coinciding with the centerline of the barrel <NUM> and its longitudinal bore 23d formed therein between the muzzle and breech ends 23a, 23b.

The receiver <NUM> slideably supports an axially movable bolt assembly <NUM> (see, e.g., <FIG>). Bolt assembly <NUM> may include a laterally extending bolt handle 25a for manually closing or opening the breech (i.e., cycling the action). The bolt assembly <NUM> is slideably moveable forward/rearward in an axially extending internal cavity 21a of receiver <NUM> and includes a firing pin 25b (not shown) for detonating a chambered cartridge in the rear breech end 23b of the barrel <NUM> that defines the chamber; all of which is well understood by those skilled in the art without further elaboration.

Fire control mechanism <NUM> may be any suitable mechanism operable to cycle the action and discharge the firearm. In one embodiment best shown in <FIG>, fire control mechanism <NUM> generally includes movable trigger <NUM> operably linked to spring-biased rotatable hammer <NUM> via an intermediary sear assembly <NUM>. Sear assembly <NUM> is configured to selectively engage and retain hammer <NUM> in a ready-to-fire rear cocked position, and release the hammer to the forward firing position via trigger pull for striking firing pin 25b to discharge a chambered cartridge. Both hammer <NUM> and sear assembly <NUM> are rotatably and pivotably pinned to the receiver or alternatively a firing control insert 22a mounted in the receiver <NUM>. Hammer spring assembly 31a biases hammer <NUM> toward the forward firing position.

The main body <NUM> of firearm <NUM> (e.g., chassis 27a) may be an axially elongated one-piece unitary structure in one embodiment which supports the receiver <NUM> and folding stock <NUM>. Main body <NUM> defines a longitudinally-extending and upwardly open receiver-bedding cavity <NUM> for mounting the receiver <NUM> thereto and for housing the trigger-actuated fire control mechanism <NUM>. The receiver may be partially received within cavity <NUM>, wherein the upper portion of the receiver remains exposed and the lower portion is nested within the cavity in typical fashion (see, e.g., <FIG>). Any suitable method may be used to mount the receiver <NUM> to the main body <NUM>-<NUM> of the mid-stock, such as for example fasteners (e.g., screws, bolts, pins, etc.). A downwardly open magazine well 27b is defined by the main body <NUM> which is configured for detachably mounting an ammunition magazine therein (not shown). Main body <NUM> may also comprise a downwardly extending pistol grip <NUM> in some embodiments to facilitate handling the firearm. Pistol grip <NUM> may be integrally formed with the main body as a unitary structural part thereof, or alternatively may be a discrete separate part coupled to the main body by any suitable means. Main body <NUM> further includes a trigger guard 27c in one embodiment.

Rear stock <NUM> in turn comprises a butt pad assembly <NUM> for shouldering and arcuately curved upper portion defining cheek rest <NUM>. In one embodiment, rear stock <NUM> may be formed of a non-metallic like a polymeric material such as glass reinforced nylon or other plastics. Rear stock <NUM> may therefore be made by a suitable plastic molding process, such as injection molding. Other non-metallic materials, metallic materials, or combinations thereof may be used for the rear stock.

The folding stock coupling system will now be further described. <FIG> show aspects of the stock coupling system mounted to firearm <NUM>. <FIG> show portions of the firearm and stock coupling system in isolation and greater detail.

Referring to the foregoing figures in general, the stock coupling system generally includes a hinge assembly or mechanism <NUM> for pivotably mounting rear stock <NUM> to the main body <NUM> (e.g., chassis 27a) of the firearm, and a clamping assembly <NUM> for detachably coupling the hinge mechanism to the main body.

With particular reference to <FIG> and <FIG>, hinge mechanism <NUM> includes a front hinge member <NUM> and rear hinge member <NUM> pivotably coupled to the front hinge member by hinge pin <NUM>. Rear hinge member includes an elongated hinge arm <NUM> defining hinge barrel 44a which is insertable between a pair of spaced apart hinge barrels 46a, 46b on front hinge member <NUM>. The front and rear hinge members <NUM>, <NUM> are pivotably coupled together by inserting hinge pin <NUM> through pin aperture 44b in hinge barrel <NUM> and pin apertures 44c, 44d in hinge barrels 46a, 46b. Hinge pin <NUM> captures the self-contained hinge detent spring <NUM> within the three hinge barrels for biasing the detent mechanism, as further described herein. Hinge pin <NUM> may be retained in the hinge mechanism <NUM> by a snap ring 43a in some embodiment (see, e.g., <FIG>) located below the lower hinge barrel 46b of the front hinge member <NUM> when the hinge is assembled.

Hinge arm <NUM> projects forwards and transversely laterally outwards from the body of the rear hinge member <NUM> (see, e.g., <FIG> et al. This places the pivot axis for rotating the rear hinge member <NUM> (defined by hinge pin <NUM>) and rear stock <NUM> coupled thereto offset from the longitudinal axis LA of firearm <NUM>. This allows the rear stock to be folded forward alongside the main body <NUM> of the firearm.

The body of rear hinge member <NUM> further includes a rear coupling portion <NUM> configured for fixedly coupling rear mounting extension <NUM> thereto. Rear mounting extension <NUM> has a longitudinally elongated rail-like body configured for slideably mounting one of a plurality of different rear stocks <NUM> thereto each sharing a common mounting interface, as further described herein. To accomplish the coupling, rear coupling portion <NUM> includes a pair of fastener apertures <NUM> which receive threaded fasteners <NUM> (e.g., bolts/screws) therethrough inserted from a first lateral side of the rear hinge member <NUM> (e.g., left side in the figures). Fasteners <NUM> engage threaded sockets <NUM> formed on a retention plate <NUM> mounted on an opposite second lateral side of the rear hinge member (e.g., right side in figures). Mounting extension <NUM> includes a forward portion defining a pair of fastener apertures <NUM> which become concentrically aligned with fastener apertures <NUM> on rear hinge member <NUM> when the mounting extension is placed against the right side of the rear hinge member. The rear mounting extension <NUM> is sandwiched and trapped between the retention plate <NUM> on one side and the rear coupling portion <NUM> of the hinge member <NUM> on the other side to detachably couple the extension to the hinge member when the fasteners <NUM> are tightened. Other means for detachably coupling the rear mounting extension to the rear hinge member may be used.

Hinge mechanism <NUM> is selectively movable by the user between a locked condition in which the rear hinge member <NUM> is lockingly engaged with and not movable relative to the front hinge member <NUM>, and an unlocked condition in which the rear hinge member is lockingly disengaged from and movable relative to the front hinge member. The terms lockingly engage or disengaged connotes physically interaction between the front and rear hinge members which should not be confused with and is unrelated to their pinned pivotable coupling together via hinge pin <NUM>.

To accomplish the foregoing locked and unlocked conditions of the hinge mechanism, the rear hinge member <NUM> in one embodiment comprises an manually-operated actuator in the form of an actuating button <NUM> configured to automatically lock the rear hinge member to the front hinge member <NUM> in the locked condition of the hinge mechanism <NUM>. Actuating button <NUM> is slideably mounted to the rear hinge member and manually depressible by the user. The actuating button is linearly movable between an outward position in which the actuating button is lockingly engaged with the front hinge member <NUM>, and an inward position disengaged from the front hinge member. Operating spring <NUM> biases the actuating button towards the engaged outward position. Spring <NUM> may be a helical compression spring in one embodiment as shown; however, other types of springs may be used.

To form the foregoing engaged and locked relationship with the front hinge member <NUM>, actuating button <NUM> comprises a pair of first tapered locking surfaces <NUM> mutually engageable with a corresponding pair of second tapered locking surfaces <NUM> of the front hinge member when the actuating button is in the outward position. <FIG> show front hinge member <NUM> and actuating button <NUM> in isolation and greater detail. The first tapered surfaces are spaced apart on the actuating button and the second tapered surfaces are spaced apart on the front hinge member <NUM> to create a balanced locking force therebetween when the hinge mechanism is in the locked condition. As opposite to single mating lockup surfaces, the double locking surfaces advantageously prevent the rear hinge member <NUM> and rear stock <NUM> coupled thereto from becoming unlocked in the even the firearm is jarred or dropped.

The actuating button <NUM> comprises an elongated actuator body comprising an inboard mounting portion <NUM> slideably mounted in a laterally open mounting cavity or receptacle <NUM> of rear hinge member <NUM> (best shown in <FIG>). The receptacle <NUM> may be formed in an enlarged mounting boss 69c which projects perpendicularly outwards from rear coupling portion <NUM> of rear hinge member <NUM>. Operating spring <NUM> of actuating button <NUM> is disposed inside receptacle <NUM> to engage the mounting portion <NUM> of the button. Receptacle <NUM> and mounting portion <NUM> may have complementary configured cross-sectional shapes. In one embodiment, mounting portion <NUM> has a rectangular cuboid configuration and receptacle has a rectangular cross-sectional shape. Other shapes and configurations of the mounting portion and receptacle may be used in other embodiments.

The actuator body further comprises an outboard enlarged actuating end <NUM> protruding outwards from the rear hinge member <NUM> and accessible to a user for pressing the actuating button <NUM> inwards to unlock the hinge mechanism <NUM>. Actuating end <NUM> has a greater width than the narrower mounting portion <NUM> to facilitate positive engagement by a user's finger or thumb. The outward facing surface of the actuating end <NUM> may therefore be textured (e.g., ribs, serrated, knurled, etc.) to promote a non-slip engagement by the user to actuate the button. The actuating end <NUM> is the exposed portion of the actuating button <NUM> while the mounting portion <NUM> is substantially unexposed and nested inside the rear hinge member <NUM> in receptacle <NUM>.

In one embodiment, the first tapered locking surfaces <NUM> of the actuating button <NUM> may be formed by a pair of locking tabs or protrusions <NUM> extending outwards from the body of the button (e.g., mounting portion <NUM>) in opposite directions as shown (see, e.g., <FIG>). The corresponding second tapered locking surfaces <NUM> in turn may be formed on a pair of hook-shaped locking protrusions <NUM> spaced apart on the front hinge member <NUM>. Locking protrusions <NUM> may have a recurvant shape as shown (see, e.g., <FIG>) defining locking recesses 69b which face inwardly to lockingly receive and engage locking protrusions <NUM> on actuating button <NUM> when the hinge mechanism is in the locked condition. Locking protrusions <NUM> are formed on an opposite end of the front hinge member <NUM> than the hinge barrels 46a-b. It bears noting that the locking protrusion <NUM> remain stationary when the hinge mechanism <NUM> is operated since the front hinge member <NUM> is fixedly coupled to the rear of the main body <NUM> of firearm <NUM>. The locking protrusions <NUM> on actuating button <NUM> rotate in an arcuate path relative to the front hinge member and locking protrusions <NUM> thereon. Actuating end <NUM> of actuating button <NUM> is disposed between the locking protrusions <NUM> of the front hinge member when the hinge mechanism is in the locked condition (see, e.g., <FIG>, <FIG>, and <FIG>). The actuating end <NUM> therefore into and out of the gap between locking protrusions <NUM> on the front hinge member when the rear hinge member <NUM> is swung in an arcuate path about hinge pin <NUM> between closed and open positions, respectively.

In one embodiment, the retention plate <NUM> previously described which is used to couple the stock rear mounting extension <NUM> to rear hinge member <NUM> may be configured to also prevent operating spring <NUM> from ejecting actuating button <NUM> out of its mounting receptacle <NUM>, thereby beneficially serving dual functions. To accomplish this, retention plate <NUM> includes a retention protrusion <NUM> which engages a corresponding retention tab <NUM> on the actuating button <NUM> to prevent ejection of the actuating button (see, e.g., <FIG> and <NUM>-<NUM>). Tab <NUM> engages retention protrusion <NUM> when the retention plate <NUM> is coupled to the rear hinge member <NUM>. The mounting portion <NUM> of the actuating button body may include an elongated travel window 69a which receives the retention protrusion <NUM> of the retention plate. The window allows the retention protrusion <NUM> to slide back and forth therein when the actuating button <NUM> moves inwards against the biasing action of spring <NUM> as the user depresses the button, and outwards as spring returns the button to its outwardly biased position when the user releases the button. The retention tab <NUM> located adjacent to inside end of the travel window 69a acts as a travel stop for the actuating button <NUM> in addition to preventing its ejection from the rear hinge member <NUM>. To allow the retention protrusion <NUM> of retention plate <NUM> access travel window 69a, the button mounting boss 69c of the rear hinge member <NUM> includes a corresponding elongated access window 69b (see, e.g., <FIG>) which may have a length at least coextensive with the length of travel window 69c in some embodiments. Retention tab <NUM> of actuating button <NUM> slideably travels inwards and outwards within access window 69b when the button is actuated.

The coupling mechanism used for detachably coupling the hinge mechanism <NUM> to the main body <NUM> of firearm <NUM> will now be described in greater detail. Referring initially in general to <FIG>, the front hinge member <NUM> comprises a tightenable clamp assembly <NUM> configured for detachable coupling to a double-wedge shaped Picatinny rail segment <NUM> on the rear end of the firearm main body <NUM>. The wedge-shaped Picatinny rail profile is a well-known accessory attachment rail system in the firearm arts without need for undue elaboration. Rail segment <NUM> is vertically oriented in one embodiment and comprises a pair of wedge-shaped edges <NUM> opposite each other which extend laterally outwards right and left (see, e.g., <FIG> and <FIG>). Front hinge member <NUM> includes a pair of vertically spaced apart fixed wedges <NUM> formed integrally with the hinge member (best shown in <FIG>). Each wedge <NUM> defines an outward facing V-shaped notch <NUM> which receives and engages one of a pair of wedges <NUM> of a detachable clamping member <NUM>, which in turn defines an inward facing V-shaped notch <NUM> therebetween (see <FIG>). V-shaped notch <NUM> of the clamping member also receives and engages one of the wedge-shaped edges <NUM> of the rail segment <NUM>.

Front hinge member <NUM> further comprises another fixed wedge 75a at its hinge barrel area which defines an inward facing V-shaped notch 78b which receives and engages the remaining wedge-shaped edge <NUM> on the opposite side of the rail segment <NUM>. A through hole 79a formed in clamping member <NUM> within the V-shaped notch <NUM> receives a threaded fastener <NUM> (e.g., bolt/screw) therethrough. The threaded shaft of fastener <NUM> passes through a laterally elongated fastener passage 78a in the front hinge member <NUM> and rotatably engages a threaded bore 79b formed in barrel area of the hinge member which receives hinge pin <NUM> (see, e.g., <FIG> and <FIG>).

In operation to mount the hinge mechanism <NUM> to the firearm main body <NUM>, one wedge-shaped edge <NUM> of the Picatinny rail segment <NUM> is first inserted into notch 78b on front hinge member <NUM>. The clamping member <NUM> is then positioned over and onto the remaining wedge-shaped edge <NUM> of rail segment <NUM> and wedges <NUM> of the front hinge member <NUM> which are both received in notch <NUM> of the clamping member. Threaded fastener <NUM> is then inserted through clamping member <NUM> and a transversely oriented fastener hole 79c formed through the Picatinny rail segment <NUM> to engage threaded bore 79b on front hinge member <NUM>. The fastener is tightened which fixedly secures the hinge mechanism <NUM> to the firearm main body <NUM> in a rigid manner as shown in <FIG> et al. To dismount the hinge mechanism for mounting to another firearm with a similar Picatinny rail mounting interface, the process is simply reversed.

Referring generally to <FIG> and <FIG>, the rear mounting extension <NUM> fixedly coupled to the rear hinge member <NUM> as previously described herein extends rearward from the rear hinge member when the hinge mechanism is in the locked condition and defines a stock axis SA. The mounting extension <NUM> and concomitantly rear stock <NUM> mounted thereto is pivotably movable between (<NUM>) an unfolded inline position relative to the main body <NUM> and longitudinal axis LA of the firearm for firing (see, e.g., <FIG>), and a folded offset position for storage/carrying (<FIG>). Stock axis SA is parallel and substantially coaxial with the longitudinal axis LA falling within at least the same vertical plane which extends through the longitudinal axis. In the folded offset position, the stock extends forward from the hinge mechanism <NUM> and may be positioned generally parallel to longitudinal axis LA alongside firearm main body <NUM>. Stock axis SA may be parallel to but laterally offset from longitudinal axis LA.

To retain the stock <NUM>/rear mounting extension <NUM> in the folded offset position, a detent mechanism <NUM> is provided. <FIG>, <FIG>, and <FIG> show various features of the detent mechanism. The detent mechanism comprises detent protrusion <NUM> formed at the bottom of the rear hinge member hinge barrel 44a which is selectively insertable into a mating detent recess <NUM> formed in the lower hinge barrel 46b of the front hinge member <NUM>. Protrusion <NUM> defines a pair of side tapered detent surfaces <NUM> engageable with a mating pair of detent surfaces <NUM> formed at the sides of the detent recess. Detent spring <NUM> coiled around hinge pin <NUM> biases the hinge barrel 44a of rear hinge member <NUM> and detent protrusion <NUM> formed thereon downwards into the detent recess <NUM> when the stock is folded. Spring <NUM> provides a vertically reciprocating piston action when the stock is moved between the unfolded and folded positions. Hinge barrel 44a of the rear hinge member is therefore vertically displaceable relative to the hinge barrels 46a-b of front hinge member <NUM>.

In operation, the detent protrusion <NUM> is removably engaged with detent recess <NUM> when the stock <NUM> is folded forward (<FIG>). When the stock is arcuately rotated rearward inline with the firearm in the unfolded position, the detent protrusion <NUM> rides upward out of recess <NUM> as hinge barrel 44a rotates and enters a pocket <NUM> in front hinge member <NUM> thereby compressing detent spring <NUM>. The protrusion <NUM> becomes removable seated on seating surface <NUM> within pocket <NUM> while the spring remains compressed. When the stock is rotated back to the folded position, the detent protrusion <NUM> is forced downwards by spring <NUM> to re-engaged detent recess <NUM>. The dual pairs of mutually engaged tapered detent surfaces <NUM>, <NUM> of the detent mechanism act to retain a stable folded position of the stock <NUM> to resist being jarred out of position better than a single pair.

The universal stock mounting interface of the stock coupling system will now be briefly described. The rearwardly and axially extending rear mounting extension <NUM> of the folding stock coupling system may be configured for mounting a plurality of different stocks <NUM> thereto having a common mounting configuration or profile. The mounting extension therefore advantageously provides a common mounting interface compatible with mounting the plurality of different rear stocks <NUM> thereto. This allows a user to select from among numerous stocks to suite personal preferences. The rear stocks may be AR-<NUM> type stocks in one embodiment; representative examples of which are shown in the figure and particularly <FIG> in isolation. The plurality of "different" stocks as used herein which share a common mounting profile are differentiated by at least one characteristic, such as without limitation configuration (including size and shape), material of construction, surface texture, or other features. For example, <FIG> and <FIG> show two different stocks <NUM> and 26a which in this case have different configurations, but share a common mounting profile or interface for AR015 type stocks, as further described below.

Referring now to <FIG> and <FIG>which show various aspects of the rear mounting extension <NUM> and stock <NUM>, the stock has a generally tubular and forwardly open internal longitudinal passage <NUM> extending from the front to rear end of the stock. Mounting extension <NUM> is configured for slideable insertion into longitudinal mounting passageway of common cross-sectional configuration formed in each of the plurality of stocks.

In cross-sectional profile, passage <NUM> comprises a non-polygonal upper portion <NUM> and polygonal lower portion <NUM> contiguously open to the upper portion. Upper portion <NUM> may be circular and lower portion <NUM> may be rectilinear in cross-sectional profile in one embodiment as shown. This is a typical mounting configuration for AR-<NUM> rifle type stocks which are normally mounted on non-folding buffer tubes in standard AR-<NUM> rifles.

Rear mounting extension <NUM> has features which generally complement the cross-sectional profile of the plurality of stocks <NUM> to provide a relatively snug fit in the longitudinal passage <NUM> of the stocks. Rear mounting extension <NUM> has a longitudinally elongated rail-like body which may be considered somewhat I-beam shaped (see, e.g., <FIG>). Mounting extension <NUM> includes a longitudinally-extending vertical web 52a, arcuately curved upper flange <NUM> extending from lateral side at the top of the vertical web, and a longitudinally-extending lower rail portion <NUM> of generally rectilinear cross-sectional shape (e.g., square/rectangular). An intermediate portion of the extension therebetween comprises a pair of longitudinally-extending and laterally projecting lower flanges <NUM> at the bottom of vertical web 52a. Lower flanges <NUM> each may be obliquely angled upwards relative to that flat bottom surface of the lower rail portion <NUM> and upper flange <NUM>. The upper and lower flanges are configured and arranged to slideably enter and engage the upper circular portion <NUM> of the stock longitudinal passage <NUM>, whereas the lower rail portion <NUM> slideably engages the rectilinear lower portion <NUM> of passage <NUM> of the stocks.

Rear stock <NUM> is slideably adjustable in a plurality of indexed axial positions on rear mounting extension <NUM> to adjust the length of pull of the firearm to suit individual user preferences. To lock the stock in one of the selected axial positions, a plurality of longitudinally spaced apart indexed mounting holes <NUM> are formed in the bottom surface <NUM> of rear mounting extension <NUM> (see, e.g., <FIG>, <FIG>, <FIG>, and <FIG>). Holes <NUM> may be formed in an axially elongated slot <NUM> in one non-limiting embodiment. In one embodiment, holes <NUM> are threaded and receive a stock mounting bolt <NUM> which is inserted through a cylindrical vertical passage <NUM> formed through a bottom portion of the rear stock <NUM>. In other embodiments, holes <NUM> may be unthreaded to receive a spring-biased, lever-actuated stock mounting pin 59a which is provided on some AR-<NUM> rifle stock designs.

In one embodiment, the features of the front hinge member <NUM>, rear hinge member <NUM>, and actuating button <NUM> previously described herein (e.g., locking protrusions, etc.) may be integrally formed as a unitary part of a monolithic body structure as shown in <FIG>. The hinge members may be formed of any suitable metallic material. The actuating button may be formed of a metallic material or suitably strong non-metallic material (e.g., plastic) in some embodiments. The rear extension rail <NUM> is preferably formed of metal for strength to support the stock. Metallic materials which may be used for the foregoing features may comprise without limitation aluminum, titanium, steel, or combinations thereof and other metals.

A method or process for operating a folding rear stock <NUM> according to the present disclosure will now be briefly summarized. <FIG> are sequential views showing the change of hinge mechanism <NUM> between the locked and unlocked conditions previously described herein. Reference is made to these and other figures noted below.

To start the process, <FIG> shows the hinge mechanism <NUM> in the closed and locked condition with rear stock <NUM> locked into the unfolded position inline with a longitudinal axis of the firearm and ready for firing (see also <FIG> and <FIG>). Stock axis SA is inline and parallel to longitudinal axis LA of firearm <NUM>. First locking protrusions <NUM> on actuating button <NUM> are engaged with locking slots 63b on second locking protrusions <NUM> of front hinge member <NUM>. Tapered locking surfaces <NUM> and <NUM> are mutually engaged, which is maintained by the outward directed biasing force created by operating spring <NUM> on actuating button <NUM>.

Next, the method continues with the user depressing the actuating button <NUM> of a hinge mechanism as shown in <FIG> (note inward directed pressing force arrow). Button <NUM> moves inwards into rear hinge member <NUM>, thereby disengaging the pair of first locking protrusions <NUM> on the actuating button from the pair of corresponding second locking protrusions <NUM> and their locking recesses 63b on the front hinge member <NUM> to unlock the hinge mechanism.

With the hinge member unlocked and the actuating button <NUM> remaining depressed, the rear stock <NUM> on rear mounting extension <NUM> may be now rotated by the user about the pivot axis defined by the hinge pin <NUM> of the hinge mechanism as shown in <FIG>. Actuating button <NUM> may be releases and spring <NUM> returns the button to the outwards position shown. The rear stock is rotated forward until the hinge mechanism is fully opened and the rear stock is placed in the folded position alongside and adjacent main body <NUM> of the firearm (see, e.g., <FIG>). Stock <NUM> may contact main body <NUM> in some embodiments. The stock is laterally offset from the longitudinal axis LA of the firearm. The stock axis SA is substantially parallel to longitudinal axis LA. The folded position of the rear stock and open position of hinge mechanism <NUM> is maintained by the detent mechanism <NUM> on the hinge barrels 44a and 46b of the rear and front hinge members <NUM>, <NUM> respectively as previously described herein.

To return the rear stock <NUM> to the unfolded inline and ready-to-fire, the actuating button <NUM> advantageously need not be depressed (nor does any other type latching or lever mechanism need to be separately actuated). The user simply rotates the stock <NUM> rearward by hand which automatically disengages the detent mechanism <NUM>. Arcuately curved actuating surfaces 63a formed on each locking protrusion <NUM> of front hinge member <NUM> engages locking protrusions <NUM> on actuating button <NUM> as the hinge is closed. This forces the actuating button inwards temporarily against the force of spring <NUM> as the locking protrusions <NUM> slide along the actuating surfaces 63a. When the locking recesses 63b become aligned with the locking protrusions <NUM> on the button, the button will snap back outwards to re-engage locking protrusions <NUM> with the locking recess to reestablish the fully closed and locked condition of the hinge mechanism <NUM>. Stock <NUM> is again inline and ready-to-fire.

Variations of the foregoing method and order of steps are possible within the scope of the invention as claimed in the appended set of claims.

Claim 1:
A stock coupling system for a firearm (<NUM>), the stock coupling system comprising:
a longitudinal axis (LA);
a hinge mechanism (<NUM>) comprising a front hinge member (<NUM>) configured to be fixedly coupled to a main body (<NUM>) of the firearm (<NUM>), and a rear hinge member (<NUM>) pivotably coupled to front hinge member;
the hinge mechanism (<NUM>) selectively movable between a locked condition in which the rear hinge member (<NUM>) is not movable relative to the front hinge member (<NUM>), and an unlocked condition in which the rear hinge member is movable relative to the front hinge member;
an actuating button (<NUM>) movably mounted to the hinge mechanism (<NUM>), the actuating button being configured to lock the rear hinge member (<NUM>) to the front hinge member (<NUM>) in the locked condition of the hinge mechanism (<NUM>); and
an elongated rear mounting extension (<NUM>) coupled to the rear hinge member (<NUM>), the rear mounting extension configured to detachably couple a rear stock (<NUM>) thereto;
wherein the actuating button (<NUM>) is linearly movable between an outward position in which the actuating button is lockingly engaged with the front hinge member (<NUM>) and an inward position disengaged from the front hinge member;
an operating spring (<NUM>) which biases the actuating button towards the outward position;
a retention plate (<NUM>) fixedly coupling the rear mounting extension (<NUM>) to the rear hinge member (<NUM>) via a pair of fasteners (<NUM>) passing through the rear hinge member (<NUM>) and rear mounting extension to threadably engage the retention plate;
wherein the retention plate (<NUM>) further comprises a retention protrusion (<NUM>) which engages a corresponding retention tab (<NUM>) on the actuating button (<NUM>) to prevent ejection of the actuating button by the operating spring (<NUM>).