Patent Description:
There are a number of available automatic and semi-automatic firearms for use by military personnel and civilians. While fully automatic firearms are generally illegal for use by the civilian population, many of the components which constitute an automatic firearm are the same as those found within legal semi-automatic models. Arguably the most popular semi-automatic assault-type firearm used by civilians, particularly within the United States, is the AR-<NUM> ® firearm. The AR-<NUM> ® is the semi-automatic variant of the fully automatic M16 firearm used by United States military personnel. While AR-<NUM> ® is a registered trademark of Colt Industries, a number of additional manufacturers manufacture clones of the AR-<NUM> ® and market these clones under separate trademarks. While used throughout the specification, it is to be understood that the term AR-<NUM> ® is meant to include not only those firearms manufactured by Colt Industries, but also those additional clones and any variants thereof.

The AR-<NUM> ® firearm and M16 are designed as modular rifles generally comprising a buttstock, lower receiver, upper receiver and barrel assembly configured to fire. <NUM> Remington or <NUM>×<NUM> NATO military ammunition. Each component is separable from one another and affords firearm owners the opportunity to customize the firearm with after-market components such as barrels of differing lengths, upper receivers designed to handle different calibers of rifle ammunition, flashlights, hand guards, grenade or flare launchers, flash or sound suppressors, grips, and front or rear sights. To operate, the lower receiver is configured to include a trigger wherein activation of the trigger causes a rifle cartridge housed within the chamber of the upper receiver to be fired out the barrel of the firearm by action of a reciprocating bolt carrier group. Internal mechanisms of the upper receiver expel the shell casing of the fired rifle cartridge from the chamber while components engaged with the magazine housed within the magazine well of the lower receiver feed a new rifle cartridge into the now-empty chamber. The buttstock mounts to the lower receiver and includes a buffer assembly and action (or recoil) spring in communication with the bolt carrier group where the spring pushes the bolt carrier group back toward the chamber in preparation of firing another rifle cartridge.

To date, most automatic and semi-automatic firearms, like the AR-<NUM> ® firearm, have been configured to fire rifle cartridges only. Attempts to modify these firearms, and particularly the AR-<NUM>, to fire shotgun shells have run into a number of problems. For instance, AR-<NUM> ® firearms have been modified to accommodate. <NUM> bore shells but these modifications require lower receivers which no longer satisfy military specifications (mil-spec). Other modifications continue to result in jamming or binding of the shotgun shell cartridges when a cartridge has been fired, its shell is being ejected, or a new cartridge is being extracted from the magazine and loaded within the chamber. To that end, Applicant has produced a shotgun shell magazine configured to feed shells from the magazine into a mil-spec AR-<NUM> ® firearm/M16 lower receiver (see commonly owned <CIT>. ) Nevertheless, the direct impingement mechanism used within many assault-type rifles (including the M16/AR-<NUM> ® firearm) may hinder or prevent proper ejection of the fired shotgun shell, or may fail to properly cycle the bolt carrier assembly during ejection and extraction.

As disclosed within the `<NUM> application, an upper receiver and barrel assembly has been configured to mount to a lower receiver, wherein fired shotgun shells may be efficiently ejected after firing while also properly extracting the next successive shotgun shell from the magazine upon proper cycling of the bolt carrier assembly. The modified M16/AR-<NUM> ® firearm upper receiver is configured to mount to a mil-spec M16/AR-<NUM> ® firearm lower receiver and automatically or semi-automatically fire. <NUM> bore shotgun shells.

While the assembly disclosed within the `<NUM> application has enabled firing of. <NUM> bore shotgun shells using a mil-spec M16/AR-<NUM> ® firearm lower receiver, the variance in energy discharge from commercially available. <NUM> bore shotgun shells requires an operator to select/adjust the piston spring and/or buffer spring of the firearm so as to ensure proper cycling of the action. That is, should the piston spring and/or buffer spring be too firm, insufficient spring compression will occur such that the fired shell is not ejected from the chamber or the next live shell is not stripped from the magazine. Conversely, should the piston spring and/or buffer spring be insufficiently firm, the piston and/or bolt carrier group and/or buffer may energetically impact the body of the firearm, potentially damaging the various components which are impacted. Thus, there is a need for an adjustable gas piston assembly which includes a selectively adjustable gas regulator which can be quickly and easily adjusted so as to maintain proper cycling of the action when using a variety of commercially available. <NUM> bore shotgun shells. The present invention addresses these and other needs.

In general, an embodiment the present invention is directed to an upper receiver and barrel assembly configured to mount to a lower receiver and receive and fire a shotgun shell. The upper receiver and barrel assembly comprises an upper receiver, a barrel assembly and a gas piston assembly. The upper receiver comprises an upper receiver housing defining a chamber configured to receive the shotgun shell therein and a bolt carrier group. The bolt carrier group includes a bolt carrier slidably received within the upper receiver housing, wherein the bolt carrier travels from a forward position to a rearward position upon firing of the shotgun shell; a bolt received within the bolt carrier; a firing pin configured to strike a primer end of the shotgun shell when the bolt carrier is in the forward position; and an ejector assembly including an ejector pin and ejector hook, wherein the ejector assembly is configured to expel the fired shotgun shell from the chamber when the bolt carrier travels to the rearward position. The barrel assembly comprises a barrel having a receiver end and a muzzle end and a tubular sidewall defining an open bore; a barrel extension coupling the receiver end of the barrel to the upper receiver housing; and a barrel nut adapted to releasably secure the barrel and barrel extension to the upper receiver housing, The gas piston assembly comprises a piston body having a first end and a second end, wherein the first end of the piston body includes a tab slidably received within a corresponding slot defined by the barrel extension; a piston end cap coupled to the second end of the piston body; a piston bonnet having a bonnet end wall and a sidewall configured to slidably receive the piston end cap therein, wherein the piston bonnet is secured to the barrel an intermediate distance between the receiver end and the muzzle end of the barrel, wherein a piston gap is defined between the piston end cap and the bonnet end wall, and wherein the barrel sidewall defines a gas port fluidly connecting the open bore of the barrel with the piston gap; and a biasing member urging the piston body and piston end cap toward the bonnet end wall.

In accordance with the present invention as defined in claim <NUM> as appended hereto there is provided a gas piston assembly suitable for use within a modular firearm. The gas piston assembly comprises a piston apparatus having a first end and a second end wherein the piston apparatus is configured to be coaxially mounted onto a barrel of the modular firearm; a piston bonnet configured to be coaxially mounted onto the barrel, the piston bonnet having a bonnet end wall with a bonnet aperture defined therethrough and a bonnet sidewall configured to slidably receive the second end of the piston apparatus therein, wherein a piston gap is defined between the second end of the piston apparatus and the bonnet end wall and is in communication with the bonnet aperture; and a selectively adjustable gas regulator in communication with the bonnet aperture and configured to selectively occlude the bonnet aperture in fully open, partially open and fully closed orientations. Preferred features are set out in the dependent claims.

The bonnet end wall may also include a threaded bore perpendicular to and in communication with the bonnet aperture while the gas regulator includes a threaded shaft proportioned to be threadably received within the threaded bore and translatable to selectively occlude the bonnet aperture in the fully open, partially open and fully closed orientations. The threaded shaft includes a head portion adapted to be gripped by a user to threadably translate the threaded shaft and a detent may be configured to engage one recess of a series of annularly spaced recesses defined on a bottom face of the head portion of the threaded shaft as the threaded shaft is rotationally translated.

Additional objects, advantages and novel features of the present invention will be set forth in part in the description which follows, and will in part become apparent to those in the practice of the invention, when considered with the attached figures.

The accompanying drawings form a part of this specification and are to be read in conjunction therewith, wherein like reference numerals are employed to indicate like parts in the various views, and wherein:.

Referring to the drawings in detail, and specifically to <FIG>, a prior art firearm, such as the AR-<NUM> ® firearm, is generally indicated by reference numeral <NUM>. Firearm <NUM> may be a modular firearm consisting of a number of components and subcomponents. Major components of firearm <NUM> may include lower receiver assembly <NUM>, upper receiver assembly <NUM>, buttstock assembly <NUM> and barrel assembly <NUM>. To assemble a completed firearm, upper receiver assembly <NUM> is coupled to lower receiver assembly <NUM> while buttstock assembly <NUM> is connected to the lower receiver assembly <NUM> and barrel assembly <NUM> is mounted onto upper receiver assembly <NUM>. Lower receiver assembly <NUM> is configured to include a magazine well <NUM> adapted to slidably receive a magazine <NUM> therein. Magazine <NUM> may carry one more cartridges, bullets or shells <NUM> which may be serially loaded within a chamber <NUM> in upper receiver assembly <NUM>. Activation of the firing mechanism (not shown) is controlled by trigger <NUM>. A grip <NUM> (such as a pistol grip, as shown) allows the user to aim and control the firearm while placing the user's trigger index finger in close proximity to the trigger. In this manner, the user can aim the firearm to the target and extend the trigger index finger to engage the trigger without losing control or accuracy of the firearm. A charging handle assembly <NUM> including a charging handle <NUM> and release/retaining lever <NUM> is provided for opening and controlling a bolt carrier group (not shown) for maintenance, loading the first live unfired cartridge into chamber <NUM> and removing a live unfired cartridge from the chamber, as is known in the art.

Most assault-type firearms are configured to be operated as rifles and include a rifled barrel and are chambered to receiver and fire rifle cartridges. By way of example, the most ubiquitous civilian assault weapon, the AR-<NUM> ® firearm, is generally chambered for standardized rounds such as the Remington. <NUM> cartridge or the <NUM>×<NUM> NATO military cartridge. The major components of the AR-<NUM> ® firearm have been standardized, with such standardization being generally referred to as meeting United States Military Standards or, more commonly as being "mil-spec". Specifically, as used herein, the terms "mil-spec" and "mil-spec M16/AR-<NUM> ® firearm" shall refer to the structural specificities defined by the United States Department of Defense as of January <NUM>, <NUM> the date of filing of <CIT>.

Assault weapons, such as the AR-<NUM> ® firearm, have also been modified to chamber and fire. <NUM> bore shotgun shells. However, these firearms suffer from a number of drawbacks. For instance, <NUM> inch (<NUM>) long shotgun shells tend to bind within the chamber and/or magazine thus leading to performance failures. In an attempt to alleviate these binding issues, firearms have been modified such that the magazine well of the lower receiver is slightly larger than the standard AR-<NUM> ® firearm magazine well such that the larger magazine well can receive a larger magazine such that the shotgun shells can be more repeatably extracted from the magazine and chambered within the upper receiver. This modification, however, renders the lower receiver assembly no longer mil-spec and also leads to difficulties when mating the upper and lower receivers. While the magazine which is the subject of the '<NUM> Patent addresses these issues by providing a magazine which may be mounted within a mil-spec AR-<NUM> ® firearm lower receiver, efficient ejection of fired shotgun shells and proper cycling of the bolt carrier assembly may be enhanced by a modified mil-spec AR-<NUM> ® firearm upper receiver and barrel assembly as described below.

To that end and with reference to <FIG>, an exemplary upper receiver and barrel assembly <NUM> in accordance with an aspect of the present disclosure may generally comprise an upper receiver <NUM>, barrel assembly <NUM> and gas piston assembly <NUM>. In one aspect of the present disclosure, upper receiver <NUM> includes an AR-<NUM> ® firearm upper receiver body <NUM> configured to mount to a mil-spec AR-<NUM> ® firearm lower receiver body. To that end, upper receiver body <NUM> includes first and second nodules <NUM>, <NUM> proportioned to rest within a notch or groove formed within the sidewalls of the mil-spec AR-<NUM> ® firearm lower receiver body (not shown). Each nodule and respective sidewall includes corresponding through-holes whereby a respective pin (not shown) may be inserted within each corresponding through-hole to secure the two receiver bodies together.

Upper receiver body <NUM> may originate as a mil-spec AR-<NUM> ® firearm upper receiver but may be modified so as to define a chamber <NUM> that has been proportioned to accommodate <NUM> inch (<NUM>) long. <NUM> bore shotgun shell cartridges. Ejection port <NUM> may also be enlarged in relation to a mil-spec AR-<NUM> ® firearm upper receiver configured to fire rifle cartridges so as to provide additional clearance for ejection of the longer <NUM> inch (<NUM>) <NUM> bore shotgun cartridge casings when compared to the shorter <NUM> inch long. <NUM> Remington (<NUM>. 56x45mm NATO) rifle cartridge casings. In a further aspect of the present disclosure, upper receiver body <NUM> may be further modified to include provision of ejector hook <NUM> configured to engage an ejector pin <NUM> carried by bolt carrier group <NUM> as will be discussed in greater detail below. Upper receiver body <NUM> may also include a notched portion <NUM> configured to receive a charging handle assembly, such as charging handle assembly <NUM> described above with reference to <FIG>.

With additional reference to <FIG>, upper receiver housing <NUM> receives bolt carrier group <NUM> therein. Bolt carrier group <NUM> may generally comprise bolt carrier <NUM>, bolt <NUM>, firing pin <NUM> and ejector pin <NUM>. Bolt carrier <NUM> may also include a groove <NUM> within which translates ejector hook <NUM> when bolt carrier group <NUM> cycles during operation, as will be discussed in greater detail below. Upper receiver housing <NUM> may also include a forward assist <NUM> configured to manually advance bolt carrier <NUM> to its forward position, if necessary, as is known in the art.

With further reference to <FIG>, the distal end of bolt <NUM> may include a bolt head <NUM> configured to extract and eject shotgun shell cartridges, as well as lock and unlock within barrel extension <NUM>, as will be discussed in greater detail below. To that end, bolt head <NUM> may include a cartridge guide <NUM> and opposing cartridge extractor <NUM>. Cartridge guide <NUM> may be integrally formed with bolt head <NUM>. Extractor <NUM> may generally comprise a T-shaped member, wherein the vertical trunk 235b is pivotally received within a cavity within the body of bolt head <NUM> via an extractor pin <NUM>. Proximal end 235c is configured to overlap extractor spring <NUM> whereby distal end 235d is biased toward extractor <NUM>. Cartridge guide <NUM> and extractor <NUM> may each include a respective hook 233a, 235a projecting inwardly toward the center of bolt head <NUM>. Hooks 233a, 235a thereby define a rim gap 245a, 245b between each hook and face <NUM> of bolt head <NUM>. Bolt head <NUM> also defines a firing pin through bore <NUM> within which firing pin <NUM> may translate and an ejector through bore <NUM> within which translates ejector pin <NUM>. The operation of each of these features will be described in greater detail below.

Coupled to upper receiver <NUM> is barrel assembly <NUM>. Barrel assembly <NUM> may include barrel <NUM>, barrel extension <NUM> and barrel nut <NUM>. Barrel <NUM> comprises a generally tubular sidewall <NUM> defining an open bore <NUM> extending the length of barrel <NUM> from receiver end <NUM> to muzzle end <NUM>. Barrel extension <NUM> comprises a separate tubular member having a stepped outer wall thereby delineating barrel extension <NUM> into a barrel receiving portion <NUM> and bolt receiving portion <NUM>. Bolt receiving portion <NUM> includes an external annular ring <NUM> proximate step <NUM>. Receiver end <NUM> of barrel <NUM> may include male threads configured to engage corresponding female threads defined within inner wall surface <NUM> of barrel receiving portion <NUM> of barrel extension <NUM> so as to form a unitary barrel member <NUM>. Bolt receiver portion <NUM> of barrel extension <NUM> may then slide within the forward barrel receiving end <NUM> of upper receiver body <NUM> to mount barrel member <NUM> to upper receiver body <NUM>. As shown most clearly in <FIG>, inner wall surface <NUM> of bolt receiver portion <NUM> may include one or more generally T-shaped grooves <NUM> configured to lockingly receive detents <NUM> on bolt <NUM> as bolt <NUM> is rotated into the forward position via bolt cam <NUM> riding within carrier slot <NUM>.

With reference to <FIG>, barrel nut <NUM> may comprise a generally tubular member having a stepped inner wall <NUM> including a step <NUM> defining an upper receiving portion <NUM> and a gas piston assembly portion <NUM>. Upper receiving portion <NUM> may include female threads configured to threadably engage male threads defined on forward barrel receiving end <NUM> of upper receiver body <NUM>. In this manner, barrel nut <NUM> may be tightened onto upper receiver body <NUM> so as to capture barrel extension annular ring <NUM> between step <NUM> on barrel nut <NUM> and forward barrel receiving end <NUM> and secure barrel member <NUM> to upper receiver body <NUM>. As will be discussed in greater detail below, a spaced distance <NUM> may be defined between inner wall <NUM> of gas piston assembly portion <NUM> of barrel nut <NUM> and outer wall surface <NUM> of barrel receiving portion <NUM> of barrel extension <NUM>. Barrel extension <NUM> may further define opposing slots <NUM> which are configured to slidably receive gas piston assembly <NUM> as will described in greater detail below.

Gas piston assembly <NUM> is configured to coaxially mount about barrel member <NUM> and includes a piston <NUM> generally comprised of a piston body <NUM> and piston head <NUM>. First end <NUM> of piston body <NUM> includes one or more tabs <NUM> wherein each tab <NUM> is configured to be slidingly received within a respective slot <NUM> define within barrel extension <NUM>. As will be discussed in greater detail below, terminal ends <NUM> of each tab <NUM> are configured to engage respective tangs <NUM> on bolt carrier <NUM> upon firing of the shotgun cartridge (see <FIG>, <FIG> and <FIG>). In one aspect of the present disclosure, terminal ends <NUM> of each tab <NUM> abut against respective tangs <NUM> on bolt carrier <NUM> when bolt carrier <NUM> is in the forward position as shown in <FIG>, <FIG> and <FIG>. In an alternative aspect of the present disclosure, terminal ends <NUM> of each tab <NUM> are a spaced distance away from its respective tang <NUM> when bolt carrier <NUM> is in the forward position but are driven into contact with its respective tang <NUM> by operation of the gas evolved upon firing of the shotgun shell cartridge, as will be discussed in greater detail below.

Second end <NUM> of piston body <NUM> fixedly receives piston head <NUM>. Piston head <NUM> generally includes a piston end cap <NUM> coupled to a piston bushing <NUM> at a first end <NUM>, such as through a threaded connection. One or more small gas rings <NUM> may be interposed between flange <NUM> of piston end cap <NUM> and piston bushing <NUM> so as to form a gas-tight seal therebetween. Small gas rings <NUM> also form a gas-tight seal between piston head <NUM> and barrel <NUM>. First end <NUM> of piston end cap <NUM> (and piston bushing <NUM>) may then be secured within a first end <NUM> of a piston coupling <NUM>, such as through a threaded connection. One or more large gas rings <NUM> may be interposed between flange <NUM> of piston end cap <NUM> and piston coupling <NUM> so as to form a gas-tight seal therebetween. Second end <NUM> of piston coupling <NUM> may then be secured to second end <NUM> of piston body <NUM>, such as through a threaded connection. In this manner, piston body <NUM> and piston head <NUM> may form a unitary body, i.e. piston <NUM>.

To provide for reciprocal travel of piston <NUM>, as will discussed in greater detail below, gas piston assembly <NUM> further includes a bonnet <NUM>, retaining ring <NUM> and bonnet cap <NUM>. Bonnet <NUM> includes a stepped sidewall <NUM> generally delineating a piston receiving portion <NUM> and bonnet cap receiving portion <NUM>. Piston receiving portion <NUM> is configured to slidingly encircle first end <NUM> of a piston coupling <NUM>, piston end cap <NUM> and large gas rings <NUM>. Large gas rings <NUM> are proportioned so as to form a gas-tight seal between bonnet <NUM> and piston head <NUM>. Bonnet cap receiving portion <NUM> includes a stepped internal face <NUM> configured to receive retaining ring <NUM> and a threaded external face <NUM> configured to threadably receive bonnet cap <NUM> thereon. A set screw <NUM> may releasably lock bonnet cap <NUM> on bonnet <NUM>. Retaining ring <NUM> is configured to reside within an annular recess <NUM> defined by recess walls <NUM> along barrel <NUM> (see <FIG>) and may be comprised of two generally C-shaped members. Retaining ring <NUM> may thus operate as a piston stop along the length of barrel <NUM>. For instance, bonnet <NUM> is prevented from lateral travel toward muzzle end <NUM> through engagement of retaining ring <NUM> upon recess wall <NUM>. Piston coupling <NUM>, and thus piston <NUM>, is in turn prevented from lateral travel toward muzzle end <NUM> by engagement of coupling step <NUM> of piston coupling <NUM> against terminal end <NUM> of bonnet <NUM>.

As can be seen in <FIG> and as will be discussed in greater detail below, a piston gap <NUM> is defined between flange <NUM> of piston end cap <NUM> and bonnet end wall <NUM>. Piston gap <NUM> is positioned to coincide with a gas port <NUM> defined within barrel sidewall <NUM> so as to create a fluid pathway between open bore <NUM> and piston gap <NUM>. The longitudinal axis of gas port <NUM> may be oriented at an angle A with respect to the longitudinal axis of bore <NUM> of barrel <NUM>. In one aspect of the present disclosure, angle A is selected to be between about <NUM>° and about <NUM>°, between about <NUM>° and about <NUM>°, or about <NUM>°, although any angle may be defined so long as gas port <NUM> operates in accordance with the teachings of the present invention, as will be discussed in greater detail below.

Lateral travel of bonnet <NUM> toward receiver end <NUM> is prevented by the threaded engagement of bonnet cap <NUM> to bonnet <NUM> and the interference of retaining ring <NUM> against internal face <NUM> of bonnet cap <NUM>. However, piston <NUM> is free to slidably translate along barrel <NUM> toward receiver end <NUM> as will be discussed in greater detail below. To that end, a biasing member, such as piston spring <NUM>, may urge piston <NUM> toward the inner surface <NUM> of bonnet end wall <NUM>. For instance, first end <NUM> of piston spring <NUM> may rest upon end face <NUM> of barrel nut <NUM> while second end <NUM> may rest against end face <NUM> of piston coupling <NUM>.

Turning now to <FIG>, operation of the various features of the exemplary upper receiver and barrel assembly <NUM> are shown. With reference to <FIG>, the firearm is loaded with a shotgun shell cartridge (not shown) and is ready to be fired. That is, the rimmed edge of a. <NUM> bore shotgun shell cartridge is received within rim gap 245a, 245b such that the primer end of the sell cartridge lies flush against bolt head face <NUM> (see e.g., <FIG> and <FIG>). As shown, piston <NUM> is in the forward position with coupling step <NUM> contacting terminal end <NUM> of bonnet <NUM> and tabs <NUM> of piston <NUM> contacting tangs <NUM> on bolt carrier <NUM>. However, as described above, tabs <NUM> of piston <NUM> may initially be a spaced distance from tangs <NUM> on bolt carrier <NUM>. Upon firing of the shotgun shell cartridge, such as through actuation of the trigger (not shown, see e.g., <FIG>) to drive firing pin <NUM> into the primer end of the cartridge (not shown), a volume of hot, high pressure gas <NUM> is evolved. High pressure gas <NUM> travels down barrel <NUM> toward muzzle end <NUM> and operates to propel and expel the shotgun shell contents (i.e., bird shot, buckshot or slugs) out of barrel <NUM>.

With reference to <FIG>, as high pressure gas <NUM> travels down barrel <NUM>, a portion <NUM> of the gas is directed into piston gap <NUM> by way of gas port <NUM>. Gas portion <NUM> impinges upon flange <NUM> of piston end cap <NUM>. The pressure of gas portion <NUM> is sufficient to overcome the biasing force of piston spring <NUM> such that piston <NUM> translates toward receiver end <NUM> in direction F as generally indicated by arrow <NUM>. Travel of piston <NUM> causes potential energy to be stored within piston spring <NUM>. As tabs <NUM> engage tangs <NUM> of bolt carrier <NUM>, bolt carrier group <NUM> is also translated in direction F within upper receiver body <NUM>. The fired, empty shell travels with bolt carrier group <NUM> as the rimmed edge of the shell is still captured within rim gap 2454a, 245b formed by cartridge guide <NUM> and extractor <NUM>. In accordance with an aspect of the disclosure, gas port <NUM> is configured to be at about a <NUM>° angle toward receiver end <NUM>. Gas port <NUM> may have an internal diameter between about <NUM> inches and about <NUM> inches, or between about <NUM> inches and <NUM> inches. In this manner, a suitable volume and pressure of gas portion <NUM> may be introduced into piston gap <NUM>.

As shown in <FIG>, gas portion <NUM> continues to translate piston <NUM> and bolt carrier group <NUM> in direction F until piston end cap <NUM> clears terminal end <NUM> of bonnet <NUM> whereby gas portion <NUM> may vent to atmosphere. Travel of piston <NUM> in direction F may also be halted by physical engagement of first end <NUM> of piston body <NUM> against step <NUM> of barrel extension <NUM> (i.e., gap <NUM> is closed); see <FIG>. Upon venting of gas portion <NUM>, piston <NUM> may then return to the forward position by traveling in opposing direction R as indicated generally by arrow <NUM> due to the release of the stored potential energy in piston spring <NUM>. First end <NUM>, large gas rings <NUM> and piston end cap <NUM> of piston <NUM> may then reset within bonnet <NUM> as described above in preparation of firing the next shotgun cartridge.

While piston <NUM> is reset as described above, bolt carrier group <NUM> may unlock from barrel extension <NUM> (<FIG>), such as through rotation of cam <NUM> in carrier slot <NUM> (see <FIG>), and thereby continue to travel in direction F due to inertia (along with the fired, empty shell). Continued travel of bolt carrier group <NUM> in direction F causes ring portion <NUM> of ejector pin <NUM> to engage flange <NUM> of ejector hook <NUM> while the remainder of bolt carrier group <NUM> continues to travel in direction F. As a result, pin extension <NUM> of ejector pin <NUM> may then extend outwardly of bolt <NUM> into chamber <NUM> so as to engage the rimmed edge of the fired, empty shotgun shell (not shown). In one aspect of the disclosure, ejector pin <NUM> engages the rimmed edge of the fired, empty shotgun shell proximate cartridge guide <NUM> so as to apply a force off-center from the central axis of the shotgun shell. Application of force against one side of the shell may cause the rimmed edge to slip past extractor <NUM> so as to "flip" the used shell from the bolt. In this manner, the fired shotgun shell may be ejected through ejection port <NUM>. In another aspect of the disclosure, extractor <NUM> may pivot about extractor pin <NUM>, thereby compressing extractor spring <NUM> and opening rim gap 245a so as to assist ejection of the fired, empty shotgun shell. Once the shell has been ejected, the potential energy within the compressed extractor spring may be released, thereby returning extractor <NUM> to its original position.

Travel of bolt carrier group <NUM> in direction F against a buffer spring housed within the buttstock assembly (see e.g., <FIG>) causes potential energy to be stored within the buffer spring, as is known in the art. Once the inertial energy of bolt carrier group <NUM> equals the compression force of the buffer spring, travel of bolt carrier group <NUM> in direction F is arrested. The buffer spring may then release its stored potential energy so as to redirect bolt carrier group <NUM> in the opposing direction R. As bolt carrier group <NUM> travels in direction R, bolt <NUM> may then extract the next available shotgun shell cartridge from the magazine (not shown, see e.g., <FIG>). Bolt carrier group <NUM> continues to travel in direction R until the new, live shotgun shell cartridge is seated within the chamber and bolt <NUM> reseats within barrel extension <NUM> as shown in <FIG> and <FIG>, such as through reverse rotation of cam <NUM> in carrier slot <NUM> and locking of detents <NUM> on bolt <NUM> within T-shaped grooves <NUM> defined by barrel extension <NUM> (see e.g., <FIG>).

Simultaneously, cartridge guide <NUM> and extractor <NUM> are driven against the rimmed end of the new, live shotgun shell cartridge such that the rimmed edge travels down the ramped face of hooks 233a, 235a until the rimmed edge slides past the hooks and rests within rim gap 245a, 245b. Again, extractor <NUM> may pivot about extractor pin <NUM>, thereby compressing extractor spring <NUM> and opening rim gap 245a so as to assist seating of the new, live shotgun shell cartridge within rim gap 245a, 245b. Once the shell has been seated in the gap, the potential energy within the compressed extractor spring may be released, thereby returning extractor <NUM> to its original position whereby extractor hook 235a captures the rimmed edge. Should bolt <NUM> fail to reseat properly within barrel extension <NUM>, the user may use forward assist <NUM> to manually push bolt <NUM> in direction R until proper seating is achieved. The firearm is then ready to fire the newly loaded shotgun shell cartridge so as to repeat the above progression.

In accordance with an aspect of the present disclosure, to facilitate cleaning of the firearm, including upper receiver <NUM> and bolt carrier group <NUM>, ejector hook <NUM> may be pivotally mounted in upper receiver <NUM> such that ejector flange <NUM> may be pivotally withdrawn from bolt carrier <NUM> so that bolt carrier group <NUM> may be slidably removed from upper receiver <NUM> without requiring removal of ejector hook <NUM>. Upper receiver <NUM> and bolt carrier group <NUM> may then be cleaned and maintained in accordance with the art.

In view of the above, it should be further recognized that specifications of the various components must be tightly controlled to ensure proper operation of the firearm, such as and without limitation thereto, the weight, density, surface contact/friction, gap dimension and location, and spring constants.

For instance, as described above, to ensure proper cycling of piston <NUM> and bolt carrier group <NUM>, gas port <NUM> must be dimensioned, located and oriented such that sufficient gas volume and pressure is delivered to piston <NUM> to impart the needed kinetic energy to bolt carrier group <NUM>. Piston head <NUM> must also be properly sealed within bonnet <NUM> to minimize, and preferably prevent, leakage of gas portion <NUM> prior to the complete travel of piston <NUM> and venting of gas portion <NUM> as described above. Accordingly, the length of piston receiver portion <NUM> of bonnet <NUM> and the length of gap <NUM> must be proportioned such that piston <NUM> may sufficiently impart enough kinetic energy to bolt carrier group <NUM> while also allowing piston <NUM> to be reset within bonnet <NUM> prior to firing of the next successive shotgun shell cartridge. By way of example, if either the length of piston receiver portion <NUM> or gap <NUM> is too short, piston <NUM> will not provide sufficient kinetic energy to bolt carrier group <NUM> to permit ejection of the fired shotgun shell and extraction of the next successive cartridge from the magazine. However, should the length of gap <NUM> be too long, piston head <NUM> may travel too far in direction F such that it may not sufficiently reset within bonnet <NUM> prior to firing of the next shotgun shell cartridge. As a result, the gas portion introduced upon firing of the next shotgun shell cartridge would not provide sufficient volume and/or pressure of gas to piston <NUM>, which in turn would lead to insufficient cycling of bolt carrier group <NUM>. Conversely, if the length of piston receiver portion <NUM> is too long, piston head <NUM> will never clear terminal end <NUM> of bonnet <NUM> such that gas portion <NUM> will not vent to atmosphere. As a result, piston <NUM> will be prevented from resetting within bonnet <NUM>, thereby rendering the firearm unusable.

Similarly, as described above, the spring constant for each of the buffer spring and piston spring <NUM> must be selected to enable proper cycling of bolt carrier group <NUM> and piston <NUM>. That is, the size and spring constant of the buffer spring must be such that the spring constant is low enough that bolt carrier group <NUM> may travel sufficiently in direction F so as to eject the fired shotgun shell, but be high enough to recycle bolt carrier group <NUM> in direction R to extract the next successive shotgun shell cartridge and reseat bolt <NUM> in barrel extension <NUM> while also preventing bolt carrier group <NUM> from violently striking the buttstock. The size and spring constant of piston spring <NUM> must be such that the spring constant is low enough that piston <NUM> may travel sufficiently in direction F so as to impart the needed kinetic energy to bolt carrier group <NUM> while also being high enough to reset piston head <NUM> within bonnet <NUM> as described above.

Turning now to <FIG>, an alternative embodiment of an upper receiver and barrel assembly in accordance with the present invention is identified by reference numeral <NUM>. Upper receiver and barrel assembly <NUM> generally comprises an upper receiver <NUM>, barrel assembly <NUM>, gas piston assembly <NUM> and handguard <NUM>. In one aspect of the present invention, upper receiver <NUM> includes an AR-<NUM> ® firearm upper receiver body <NUM> configured to mount to a mil-spec AR-<NUM> ® firearm lower receiver body. To that end, upper receiver body <NUM> includes first and second nodules <NUM>, <NUM> proportioned to rest within a notch or groove formed within the sidewalls of the mil-spec AR-<NUM> ® firearm lower receiver body (not shown) and include a through-hole for receiving a pin to secure the two receiver bodies together.

Upper receiver body <NUM> may originate as a mil-spec AR-<NUM> ® firearm upper receiver but may be modified so as to define a chamber <NUM> that has been proportioned to accommodate <NUM> inch (<NUM>) long. <NUM> bore shotgun shell cartridges. Ejection port <NUM> may also be enlarged in relation to a mil-spec AR-<NUM> ® firearm upper receiver configured to fire rifle cartridges so as to provide additional clearance for ejection of the longer <NUM> inch (<NUM>). <NUM> bore shotgun cartridge casings when compared to the shorter <NUM> inch long. <NUM> Remington (<NUM>. 56x45mm NATO) rifle cartridge casings. Upper receiver body <NUM> may also include a charging handle assembly <NUM> similar to charging handle assembly <NUM> described above with reference to <FIG>. Upper receiver housing <NUM> may further receive a bolt carrier group therein, such as bolt carrier group <NUM> as described above, and may also include a forward assist <NUM> configured to manually advance the bolt carrier to its forward position, if necessary, as is known in the art.

Coupled to upper receiver <NUM> is barrel assembly <NUM>, which is similar to barrel assembly <NUM>, described above. Accordingly, barrel nut <NUM> may be tightened onto upper receiver body <NUM> so as to secure barrel <NUM> to upper receiver body <NUM> via male threads <NUM> on forward barrel receiving end <NUM>. As shown most clearly in <FIG>, barrel nut <NUM> may also define a pair of annular grooves <NUM> which are positioned so as to receive a respective set screw <NUM> on handguard <NUM>, as will be described in greater detail below.

Gas piston assembly <NUM> is substantially identical to gas piston assembly <NUM> except bonnet <NUM> has been swapped for bonnet <NUM> and piston spring <NUM> has been omitted. The remaining components of the gas piston assembly (piston <NUM> including piston body <NUM> and piston head <NUM> which includes piston end cap <NUM> and piston bushing <NUM>; small gas rings <NUM>; piston coupling <NUM>; large gas rings <NUM>; retaining ring <NUM> and bonnet cap <NUM>) are substantially the same and operate in a generally identical manner as their corresponding components within gas piston assembly <NUM> (piston <NUM> including piston body <NUM> and piston head <NUM> which includes piston end cap <NUM> and piston bushing <NUM>; small gas rings <NUM>; piston coupling <NUM>; large gas rings <NUM>; retaining ring <NUM> and bonnet cap <NUM>), with the exception of the adjustability of the evolved gas, which will be discussed in greater detail below with regard to bonnet <NUM>.

With reference to <FIG>, bonnet <NUM> is similar to bonnet <NUM> described above and includes a stepped sidewall <NUM> generally delineating a piston end wall <NUM> located between a piston receiving portion <NUM> and bonnet cap receiving portion <NUM>. Piston receiving portion <NUM> is configured to slidingly encircle first end <NUM> of a piston coupling <NUM>, piston end cap <NUM> and large gas rings <NUM>. Bonnet cap receiving portion <NUM> includes a stepped internal face <NUM> configured to receive retaining ring <NUM> and a threaded external face <NUM> configured to threadably receive bonnet cap <NUM> thereon. A set screw, similar to set screw <NUM> (<FIG>), may releasably lock bonnet cap <NUM> on bonnet <NUM>. Retaining ring <NUM> is configured to reside within an annular recess <NUM> defined by recess walls <NUM> along barrel <NUM> and may be comprised of two generally C-shaped members. Retaining ring <NUM> may thus operate as a piston stop along the length of barrel <NUM>. For instance, bonnet <NUM> is prevented from lateral travel toward muzzle end <NUM> through engagement of retaining ring <NUM> upon recess wall <NUM>. Piston coupling <NUM>, and thus piston <NUM>, is in turn prevented from lateral travel toward muzzle end <NUM> by engagement of coupling step <NUM> of piston coupling <NUM> against terminal end <NUM> of bonnet <NUM>.

As can be seen in <FIG>, a piston gap <NUM> is defined between flange <NUM> of piston end cap <NUM> and bonnet end wall <NUM>. Bonnet end wall <NUM> defines a bonnet aperture <NUM> therethrough which communicates with gap <NUM>. Piston gap <NUM> is positioned to coincide with a gas port <NUM> defined within barrel sidewall <NUM> so as to create a fluid pathway between open bore <NUM> and piston gap <NUM> and bonnet aperture <NUM>. The longitudinal axis of gas port <NUM> may be oriented at any angle with respect to the longitudinal axis of bore <NUM> of barrel <NUM> and, in one aspect of the present invention, is selected to be about <NUM>°. Lateral travel of bonnet <NUM> toward receiver end <NUM> is prevented by the threaded engagement of bonnet cap <NUM> to bonnet <NUM> and the interference of retaining ring <NUM> against internal face <NUM> of bonnet cap <NUM>. However, piston <NUM> is free to slidably translate along barrel <NUM> toward receiver end <NUM> as will be discussed in greater detail below.

Upon firing of the shotgun shell cartridge, such as through actuation of the trigger (not shown, see e.g., <FIG>), a volume of hot, high pressure gas <NUM> is evolved. High pressure gas <NUM> travels down barrel <NUM> toward muzzle end <NUM> and operates to propel and expel the shotgun shell contents (i.e., bird shot, buckshot or slugs) out of barrel <NUM>. As high pressure gas <NUM> travels down barrel <NUM>, a portion <NUM> of the gas is directed into piston gap <NUM> by way of gas port <NUM>. High pressure gas portion <NUM> is then further apportioned between a recharge portion <NUM> and a waste portion <NUM>. Waste portion <NUM> is vented to atmosphere by passing through bonnet aperture <NUM>.

The remaining recharge portion <NUM> impinges upon piston end cap <NUM> such that piston <NUM> translates toward receiver end <NUM>. Recharge portion <NUM> continues to translate piston <NUM> (and the bolt carrier group within upper receiver body <NUM>) until piston end cap <NUM> clears terminal end <NUM> of bonnet <NUM> whereby recharge portion <NUM> may vent to atmosphere. Travel of bolt carrier group <NUM> rearward toward the buttstock (e.g., buttstock assembly <NUM> as shown in <FIG>), causes the discharged shotgun shell to be ejected through ejection port <NUM>. Rearward movement of the bolt carrier group also causes potential energy to be stored within the buffer spring housed within the buttstock assembly (see e.g., <FIG>). Once the inertial energy of the bolt carrier group equals the compression force of the buffer spring, rearward travel of the bolt carrier group is arrested. The buffer spring may then release its stored potential energy so as to redirect the bolt carrier group in the opposing forward direction to extract the next available shotgun shell cartridge from the magazine. Movement of the bolt carrier group in the forward direction also causes piston <NUM> to return to the firing position (such as that shown in <FIG> and <FIG>) in preparation of firing the next shotgun shell cartridge.

Because there is a number shotgun shell cartridge manufacturers offering cartridges of varying firing velocities (and gas pressures), as well as differing shell payloads (i.e., bird shot, buckshot or slugs), the firearm operator needs to control the magnitude of the recharge portion <NUM> apportioned to cycle the bolt carrier group and piston assembly, as described above. That is, should the volume/pressure of the recharge portion <NUM> be too high, piston body <NUM> will drive the bolt carrier group rearward with too great a force, which in turn will compress the buffer spring with too great a force which may cause the buffer weight to strike the rear wall (buttplate) of the buttstock, thereby potentially damaging any or all of the piston, bolt carrier group, buffer weight, buffer spring or buttstock. Conversely, should the volume/pressure of the recharge portion <NUM> be too low, piston body <NUM> will impact the bolt carrier group with insufficient force to fully cycle the bolt carrier group. As a result, the discharged shotgun shell may not be properly ejected and/or the next shotgun shell cartridge may not be properly extracted from the magazine and loaded within the chamber.

With reference to <FIG>, gas piston assembly <NUM> may include a selectively adjustable gas regulator <NUM> in communication with bonnet aperture <NUM>. Gas regulator <NUM> may comprise a threaded shaft <NUM> having a first end <NUM> adapted to be threadably received within a threaded bore <NUM> defined within bonnet end wall <NUM>, wherein threaded bore <NUM> is in fluid communication with bonnet aperture <NUM>. In this manner, first end <NUM> of threaded shaft <NUM> may be selectively positioned within threaded bore <NUM> and extend within bonnet aperture <NUM> so as to selectively occlude bonnet aperture <NUM> in a fully open orientation (first end <NUM> completely removed from bonnet aperture <NUM>), a fully closed orientation (first end <NUM> abuts against or sits within a recess <NUM> defined within inner wall <NUM> of bonnet end wall <NUM>) and a partially open orientation intermediate the fully closed and fully opened orientations.

Thus, when in the fully open orientation, the maximum amount of waste portion <NUM> is vented to atmosphere with the minimum amount of recharge portion <NUM> impacting piston <NUM>. Conversely, when in the fully closed orientation, substantially all of high pressure gas portion <NUM> is directed as recharge portion <NUM> so as to impart maximum force to piston <NUM>. Minimal, if any, gas may escape bonnet aperture <NUM> as waste portion <NUM>. The ratio of recharge portion <NUM> to waste portion <NUM> may thus be selectively adjustable by selectively advancing or retreating threaded shaft <NUM> until first end <NUM> sufficiently occludes bonnet aperture <NUM> to permit proper cycling of the bolt carrier group and piston <NUM> as described above.

To assist adjustment of first end <NUM> within threaded bore <NUM>, threaded shaft <NUM> may include a second end <NUM> having a head portion <NUM> that is adapted to be gripped by the firearm operator so as to incrementally translate threaded shaft <NUM>. To that end, head portion <NUM> may be externally located relative to handguard body <NUM> of handguard <NUM> wherein handguard body <NUM> defines a regulator aperture <NUM> which is configured to overlap threaded bore <NUM> such that threaded shaft <NUM> may pass through handguard body <NUM> and threadably engage threaded bore <NUM> as described above. To promote reproducibility of threaded shaft <NUM> translation, bottom face <NUM> of head portion <NUM> may include a series of annularly spaced recess <NUM>. A detent <NUM> may be mounted onto the firearm so as to engage a selected recess <NUM>'. To that end, handguard body <NUM> may include a detent aperture <NUM> which is configured to secure detent housing <NUM> of detent <NUM> therein. Detent housing <NUM> may then include a spring <NUM>- loaded detent pin <NUM> configured to resiliently reside within selected recess <NUM>'. Thus, by rotating head portion <NUM>, threaded shaft <NUM> may be selectively translated from one recess <NUM> to another incrementally. Head portion <NUM> may also include indicia (not shown) or the firearm operator may otherwise take note of the detent pin/recess <NUM>/<NUM> and threaded shaft <NUM> position for each specific shotgun shell cartridge intended to be used within the firearm. As a result, when switching between cartridges, the operator may quickly and accurately adjust the ratio of recharge portion <NUM> to waste portion <NUM> so as to ensure proper cycling of the bolt carrier group and piston as described above.

Claim 1:
A gas piston assembly (<NUM>) suitable for use within a modular firearm, the gas piston assembly (<NUM>) comprising:
a) a piston apparatus having a first end and a second end wherein the piston apparatus is configured to be coaxially mounted onto a barrel (<NUM>) of the modular firearm;
b) a piston bonnet (<NUM>) configured to be coaxially mounted onto the barrel (<NUM>), the piston bonnet (<NUM>) having a bonnet end wall (<NUM>) with a bonnet aperture (<NUM>) defined therethrough and a bonnet sidewall (<NUM>) configured to slidably receive the second end of the piston apparatus therein, wherein a piston gap (<NUM>) is defined between the second end of the piston apparatus and the bonnet end wall (<NUM>) and is in communication with the bonnet aperture (<NUM>); and
c) a selectively adjustable gas regulator (<NUM>) in communication with the bonnet aperture (<NUM>) and configured to selectively occlude the bonnet aperture (<NUM>) in fully open, partially open and fully closed orientations.