Abstract:
The embodiments described herein relate to a sleeve piston for operating the bolt carrier of an auto-loading firearm. The sleeve piston can comprise a monolithic sleeve piston or it can comprise two or more sleeve-piston parts, thereby evenly distributing the reciprocating mass of an auto-loading firearm about its barrel and minimizing muzzle rise when fired. The sleeve piston can be coupled to the bolt carrier by two or more operating rods, thereby reducing the tipping force experienced by the bolt carrier during firearm operation. The sleeve piston can reciprocate in or on a gas block coupled to the barrel, and the sleeve piston can be removed by sliding it forward and off the end of the barrel. The embodiments of the present invention can thus provide a balanced and compact operating mechanism that is ideally suited for rifles, carbines, and personal-defense weapons.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 13/184,529, filed Jul. 16, 2011, now U.S. Pat. No. 8,640,598, which claims priority to U.S. Provisional Application No. 61/365,692, filed Jul. 19, 2010, each of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Piston-driven firearms as understood by those skilled in the art typically use an operating piston that reciprocates at some distance from a firearm barrel. An AK-47, for example, utilizes an operating piston that reciprocates above the firearm barrel. While the use of an offset operating piston can help provide reliability as compared to a direct-impingement operating system, for example, offset pistons can make semi- and especially fully-automatic firearms difficult to control because the offset piston&#39;s reciprocating mass creates a torque about the barrel. Accordingly, there is a need in the art for a firearm operating system that can provide the reliability advantages of a conventional offset piston while minimizing or even eliminating the barrel torque caused by an offset piston. Such a firearm operating system could provide numerous benefits for auto-loading firearms and would be especially useful for auto-loading rifles, carbines, and personal-defense weapons. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention generally relate to a sleeve or hollow piston that can provide the reliability of conventional piston-driven operating systems while minimizing torque about the barrel. For example, in some embodiments the sleeve piston can actuate a bolt carrier by reciprocating along a barrel in response to a gas generated by a fired cartridge. The sleeve piston can comprise any suitable shape including circular, semi-circular, or polygonal in shape, or any combination thereof. The sleeve piston of any embodiment can comprise a single or monolithic sleeve that extends around the barrel of a firearm. In the alternative, the sleeve piston can comprise two or more sleeve parts, wherein each sleeve part can be shaped or curved around a portion of the firearm barrel. One or more operating rods can couple the sleeve piston to the bolt carrier. In some embodiments, first and second operating rods can be coupled to the sleeve piston at opposite, or substantially opposite, points on the sleeve piston such as at the top and bottom or at the left and right sides of the sleeve piston. The one or more operating rods can be permanently coupled, detachably coupled, or separate from the sleeve piston in any embodiment of the present invention. For example, in embodiments where the sleeve piston is separate from two operating rods, the sleeve piston can move a predetermined distance in response to a gas before transferring an actuating or operating force to, such as by striking, the operating rods. The sleeve piston can be coupled to a bolt carrier that reciprocates in a straight line with respect to the barrel, such as to an AR-18 or M-16-type bolt carrier, in any embodiment of the present invention. The bolt carrier of any embodiment can be used with or include a bolt that reciprocates linearly with the bolt carrier. For example, in various embodiments the bolt carrier can include a non-tilting rotating bolt, such as a seven-lug AR-18 or M-16-type bolt. Embodiments of the present invention can also be used with tilting or tipping bolt carrier designs such those found in the SKS or FN FAL wherein the bolt carrier tilts or tips in order to lock into position in a receiver. The one or more operating rods can contact or strike the bolt carrier at one or more contact points or lobes. For example, in some embodiments of the present invention a first operating rod and a second operating rod contact the bolt carrier on opposite or substantially opposite points of the bolt carrier. The sleeve piston of any embodiment can include one or more gas rings on an inner surface and/or one or more gas rings on an outer surface to effectuate a gas seal. The sleeve piston of any embodiment of the present invention can be used with the methods, systems, and firearms of any embodiment of the present invention. 
     The sleeve piston of any embodiment can be movably received by a gas block to define a gas or expansion chamber. The gas block can be permanently or detachably coupled to a barrel, or the gas block and barrel can comprise a single unit in embodiments of the present invention. For example, in one embodiment a sleeve piston can comprise a circular shape and can reciprocate in a corresponding circular sleeve cylinder in a gas block to define a gas chamber. In a further embodiment a sleeve piston can reciprocate on or over a gas block, wherein the gas chamber is defined as the area between the gas block and an inner surface of the sleeve piston. The sleeve piston can be removable from the front or from the back of the gas block in any embodiment of the present invention. The gas block can be detachably coupled to the barrel by a fastener such as by one or more pins or screws, or it can be machined from the barrel itself in embodiments of the invention. One or more gas ports can couple the gas chamber to the barrel in embodiments of the invention. 
     Another embodiment of the present invention provides a system for actuating a bolt carrier of a firearm. The system of any embodiment can be integrated with, or comprise, a firearm. The system can comprise a barrel coupled to a receiver, wherein the bolt carrier is carried by the receiver. A gas chamber can receive a gas from a fired cartridge. A gas port or gas pathway can couple the barrel to the gas chamber. The sleeve piston of any embodiment of the present invention can be used to actuate or operate the bolt carrier by moving along the barrel in response to a gas or gas pressure in the gas chamber. For example, the sleeve piston can comprise a single or monolithic sleeve piston that extends around the barrel of the firearm. In the alternative, the sleeve piston can comprise two or more sleeve parts, wherein each sleeve part is shaped around a portion of a firearm barrel. One or more operating rods can couple the sleeve piston to the bolt carrier. In some embodiments, first and second operating rods can be coupled to the sleeve piston at opposite, or substantially opposite, points on the sleeve piston such as at the top and bottom, the left and right, or at the two- and 8-o&#39;clock positions of the sleeve piston. The one or more operating rods can be permanently coupled to, detachably coupled to, or independent of the sleeve piston in any embodiment of the present invention. The sleeve piston can comprise any suitable shape including circular, semi-circular, or polygonal in shape, or any combination thereof. A spring over one or more operating rods can be used to return the sleeve piston to battery in any embodiment of the present invention. In addition or in the alternative, a firearm mainspring can be used to return the sleeve piston to battery in embodiments of the present invention. 
     In further embodiments, the bolt carrier can carry or include a non-tilting rotating bolt that reciprocates co-axially with respect to the barrel, such as an AR-18, M-16, or AK-47-type bolt. The bolt can comprise as a seven-lug AR-18 or M-16-type bolt, for example. By way of further example, the bolt of any embodiment can comprise a two-lug, AK-47-type rotating bolt. The one or more operating rods can contact or strike the bolt carrier at one or more contact points or lobes. For example, in some embodiments of the present invention a first operating rod and a second operating rod contact the bolt carrier on opposite or substantially opposite points or sides of the bolt carrier. In further embodiments, a gas block is coupled to the barrel and receives the gas from the fired cartridge. The sleeve piston can be movably received by the gas block to define a gas chamber. For example, at least a portion of the sleeve piston can fit within the gas block when the system is in battery. By way of another example, at least a portion of the sleeve piston can fit over the gas block when system is in battery. The gas block of any embodiment can be permanently coupled, detachably coupled, or integrated into or with a barrel. The system of any embodiment of the present invention can be used with the apparatuses, methods, and firearms of any embodiment of the present invention. 
     Further embodiments of the present invention provide a firearm that can include the various sleeve piston apparatuses, systems, and/or methods of the present invention. In one such embodiment, the present invention provides a firearm comprising a barrel coupled to a receiver, a bolt carrier including a bolt and carried by the receiver, a sleeve piston that extends around the barrel, a gas block coupled to the barrel, and wherein the sleeve piston is movably received by the gas block to define a gas chamber that receives a gas from a projectile traveling along the barrel. The firearm can further include a gas port through which the gas flows from the barrel to the gas chamber. The sleeve piston can actuate the bolt carrier by reciprocating along the barrel in response to the gas in the gas chamber. The sleeve piston of any embodiment of the present invention can be used to actuate or operate the bolt carrier of the firearm embodiments of the present invention. For example, the sleeve piston can comprise a single or monolithic sleeve piston that extends around the barrel of the firearm. In the alternative, the sleeve piston can comprise two or more sleeve parts, wherein each sleeve part is shaped around a portion of a firearm barrel. The sleeve piston can comprise any suitable shape including circular, semi-circular, or polygonal in shape, or any combination thereof. One or more operating rods can couple the sleeve piston to the bolt carrier. In some firearm embodiments, first and second operating rods can be coupled to the sleeve piston at opposite, or substantially opposite, points on the sleeve piston such as at the top and bottom or at the left and right sides of the sleeve piston. The one or more operating rods can be permanently coupled to, detachably coupled to, or independent of the sleeve piston in any embodiment of the present invention. The sleeve piston can be coupled to a bolt carrier such as to an AR-18, M-16, or AK-47-type bolt carrier in any embodiment of the present invention. A rotating bolt, such as a seven-lug AR-18 or M-16-type bolt, can be used with the bolt carrier of any embodiment. In the alternative, a tilting bolt can also be used with any embodiment of the present invention. The one or more operating rods can contact or strike the bolt carrier at one or more contact points or lobes. For example, in some embodiments of the present invention a first operating rod and a second operating rod contact the bolt carrier on opposite or substantially opposite points or sides of the bolt carrier or bolt. A spring over one or more operating rods can be used to return the sleeve piston to battery in any embodiment of the present invention. The gas block of any embodiment, including the firearm embodiments of the present invention, can be permanently coupled, detachably coupled, or integrated into or with a barrel. 
     Yet further embodiments of the present invention provide methods for operating a bolt carrier of a firearm using a sleeve piston, wherein the firearm includes a barrel coupled to a receiver, and wherein the bolt carrier is carried by the receiver. First, the firearm is used to fire a cartridge. Second, a gas produced by the fired cartridge is directed against a sleeve piston of one or more embodiments of the present invention. Third, the sleeve piston reciprocates or is moved rearward along the barrel in response to the gas. Fourth, one or more operating rods coupled to the sleeve piston can push, strike, or transfer an actuating force to the bolt carrier. One skilled in the art will appreciate that the methods can include or be used with any of the apparatus, system, method, and firearm embodiments of the present invention. 
     One of skill in the art will understand that any feature, element, or characteristic of any embodiment of the present invention can be used or combined with any feature, element, or characteristic of any other embodiment of the present invention. Unless otherwise expressly stated, it is in no way intended that any method or embodiment set forth herein be construed as requiring that its steps or actions be performed in a specific order. Accordingly, where a method, system, or apparatus claim for example does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of embodiments described in the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention, and together with the description, serve to explain the principles of various embodiments of the invention. The embodiments described in the drawings and specification in no way limit or define the scope of the present invention. 
         FIG. 1  is a view of one embodiment of the sleeve piston of present invention. 
         FIG. 2  is another view of the sleeve piston embodiment shown in  FIG. 1 . 
         FIG. 3  is a further view of the sleeve piston embodiment shown in  FIG. 1 . 
         FIG. 4  is a view of another embodiment of the sleeve piston of present invention. 
         FIG. 5  is another view of the sleeve piston embodiment shown in  FIG. 4 . 
         FIG. 6  is a further view of the sleeve piston embodiment shown in  FIG. 4 . 
         FIG. 7  is a partial cut-away view of one embodiment of the present invention including a monolithic sleeve piston and a gas block. 
         FIG. 8  is a sectional front view of the embodiment shown in  FIG. 7 . 
         FIG. 9  is a partial cut-away view of the embodiment of  FIG. 7  with a projectile at a first time. 
         FIG. 10  is a partial cut-away view of the embodiment of  FIG. 7  with the projectile at a later time. 
         FIG. 11  is a partial cut-away view of one embodiment of the present invention including a pseudo-sleeve piston and a gas block. 
         FIG. 12  is a sectional front view of the embodiment shown in  FIG. 11 . 
         FIG. 13  is a partial cut-away view of the embodiment of  FIG. 11  with a projectile at a first time. 
         FIG. 14  is a partial cut-away view of the embodiment of  FIG. 11  with the projectile at a later time. 
         FIG. 15  is a view of a bolt carrier and bolt of one embodiment of the present invention. 
         FIG. 16  is a partial cut-away side view of the system of one embodiment of the present invention. 
         FIG. 17  shows a rifle of one embodiment of the present invention. 
         FIG. 18  illustrates the method of one embodiment of the present invention for operating the bolt carrier of a firearm. 
         FIG. 19  is a partial cut-away view of another embodiment of the present invention including a monolithic sleeve piston and a gas block. 
     
    
    
     The present invention has been illustrated in relation to embodiments which are intended in all respects to be illustrative rather than restrictive. For example, a person skilled in the art will understand that the elements in the drawings are not limited to the specific dimensions shown, but are for illustrative purposes only. Those skilled in the art will further realize that the embodiments of the present invention are capable of many modifications and variations without departing from the scope of the present invention. 
     DESCRIPTION OF THE INVENTION 
     The various embodiments of the present invention relate generally to firearms, and more specifically to the use of a sleeve or hollow operating piston that extends partially or fully around the barrel of a firearm. Any suitable firearm and/or cartridge can be used by or with the embodiments of the present invention. By way of example the firearm of any embodiment of the present invention can comprise one of a rifle, short-barreled rifle (“SBR”), personal-defense weapon (“PDW”), carbine, pistol, shotgun, machine gun, grenade launcher, or cannon. As used herein, a SBR includes a barrel that is fewer than 16 inches in overall length and a PDW includes a barrel that is fewer than 10 inches in overall length. 
     Any suitable cartridge can be used by or with embodiments of the present invention, including pistol, rifle, shotgun, and cannon cartridges. Centerfire pistol cartridges useable with embodiments of the present invention include, but are not limited to, the .32 ACP, .380 ACP, 9 mm Luger, .357 SIG, .40 SMITH &amp; WESSON, 10 mm, and .45 ACP. Centerfire rifle cartridges useable with embodiments of the present invention include, but are not limited to, the .223 REMINGTON, 5.45×39 Russian, 5.56 NATO, .243 WINCHESTER, 6.5 mm GRENDEL, 6×35 mm KAC, 6.8 mm SPC, 7 mm WINCHESTER MAGNUM, .30 REMINGTON AR, 300 AAC BLACKOUT, .30-06 Springfield, .308 WINCHESTER, 7.62 NATO, 7.62×39 Russian, .338 WINCHESTER MAGNUM, .338 LAPUA MAGNUM, .408 CHEYTAC, .416 BARRETT, .450 BUSHMASTER, .458 SOCOM, .50 BEOWULF, and .50 BMG. Shotgun cartridges or shells useable with embodiments of the present invention include, but are not limited to, the .410, 28 gauge, 20 gauge, 16 gauge, 12 gauge, and 10 gauge. 
     While embodiments of the present invention can be used with any type of weapon, the embodiments are particularly useful for automatic and semi-automatic small arms (also referred to as “auto-loading” weapons) where gas from a fired cartridge is used to actuate a bolt carrier and thereby automatically load the next cartridge. Similarly, embodiments of the present invention can include or be used with a magazine that stores a plurality of cartridges, such as with an M-16 or AK-47-type magazine. 
     Accordingly, a first embodiment of the present invention as shown in  FIGS. 1-3  provides a single or monolithic sleeve piston ( 10 ) that can extend around a firearm barrel and actuate a bolt carrier in response to a gas from a fired cartridge. The monolithic sleeve piston ( 10 ) can be coupled to one or more operating rods in embodiments of the present invention. As shown by way of example in  FIGS. 1-3 , a sleeve piston ( 10 ) can be coupled to a first operating rod ( 12 ) and a second operating rod ( 13 ), wherein the operating rods ( 12 ,  13 ) are located on opposite sides of the sleeve piston ( 10 ). The sleeve piston ( 10 ) also includes a piston face ( 11 ) that can receive gas from a fired cartridge. The inner and/or outer surfaces of sleeve piston ( 10 ) can also be used to receive gas from a fired cartridge in embodiments of the present invention, such as when the sleeve piston ( 10 ) is received over a gas block. A monolithic sleeve piston ( 10 ) can comprise a single piece, such as a single cast or milled piece of metal such as steel or titanium, or it can be comprised of one or more pieces that are permanently or detachably coupled to produce a sleeve piston ( 10 ) that can extend around the barrel of a firearm. 
     A second embodiment of the present invention as shown in  FIGS. 4-6  provides a pseudo-sleeve piston ( 20 ) comprising two or more sleeve parts ( 21 ,  22 ) wherein each sleeve part can be shaped around or along a portion of a firearm barrel. For example, as shown in  FIGS. 4-6 , a first sleeve part ( 21 ) and a second sleeve part ( 22 ) can be circular or semi-circular and therefore be shaped or curved around a firearm barrel. The sleeve piston ( 20 ) can be coupled to one or more operating rods in embodiments of the present invention. As shown by way of example in  FIGS. 4-6 , the first sleeve piston part ( 21 ) can be coupled to a first operating rod ( 25 ) and the second sleeve piston part ( 22 ) can be coupled to a second operating rod ( 26 ). Accordingly, each sleeve part ( 21 ,  22 ) can be coupled to an operating rod ( 25 ,  26 ) in embodiments of the present invention. Like the monolithic sleeve piston ( 10 ), the pseudo-sleeve piston ( 20 ) can be used to actuate a firearm bolt carrier in response to a gas from a fired cartridge. Each sleeve part ( 21 ,  22 ) such as sleeve part ( 21 ) can include a face ( 23 ) that receives a gas from a fired cartridge. In addition and/or in the alternative, the inner and/or outer surfaces of sleeve part ( 21 ,  22 ) can be used to receive gas from a fired cartridge. The sleeve piston embodiments can be used with any other embodiment of the present invention including the systems, firearms, and methods disclosed herein. 
     The sleeve piston of embodiments of the present invention, as shown by way of non-limiting example in  FIGS. 1-6 , can comprise any suitable size, shape, and/or construction. By way of example, the monolithic sleeve piston of various embodiments can comprise a circular or semi-circular, such as elliptical or oval, or polygonal shape, or any combination thereof. Similarly, the part of a pseudo-sleeve piston can comprise any suitable size, shape, and/or construction. For example, a pseudo-sleeve piston part can comprise a semi-circular, such as elliptical or oval, or polygonal shape, or any combination thereof. 
     Embodiments of the present invention also provide various sleeve piston means. As used herein, sleeve piston means includes, but is not limited to, those sleeve piston structures described with respect to  FIGS. 1-14 ,  16 - 17 , and  19 . Monolithic sleeve piston means includes to the sleeve piston structures described with respect to  FIGS. 1-3 ,  7 - 10 , and  19 . Pseudo-sleeve piston means includes those sleeve piston structures described with respect to  FIGS. 4-6  and  11 - 14 . 
     The sleeve piston of any embodiment of the present invention, such as those embodiments shown in  FIGS. 1-6 , can utilize one or more operating rods to transfer force to and thereby operate a bolt carrier. An operating rod can be permanently coupled to (such as when the sleeve piston and rod are a single manufacture), detachably coupled to, or independent from the sleeve piston in any embodiment of the present invention. By way of one example and as shown in  FIGS. 1-3 , the sleeve piston ( 10 ) and one or more operating rods ( 12 ,  13 ) can comprise a single piece of metal such as a single piece of cast or milled steel or titanium. In other embodiments the sleeve piston can be detachably coupled to one or more operating rods by means of a fastener such as a screw or pin, for example. In further embodiments the piston can be separate or independent from one or more operating rods so that the sleeve piston and the operating rod(s) can move independently from one another. In one example the sleeve piston and operating rod(s) can be independent but in direct or indirect physical contact when the bolt carrier is in battery. In further embodiments the sleeve piston can move a predetermined distance before it impacts or transfers force to one or more operating rods, thereby transferring its momentum to and operating a bolt carrier, such as the bolt carrier ( 70 ) shown in  FIG. 15 . The bolt carrier and operating rods(s) can be permanently coupled, detachably coupled, or independent in embodiments of the present invention. 
     As used herein, operating rod means includes, but is not limited to, the operating rod structures described with respect to  FIGS. 1-14 ,  16 - 17 , and  19 . 
     The operating rods of any embodiment can be coupled to the sleeve piston at any point, such as on opposite or substantially opposite points of the sleeve piston. For example, a first operating rod ( 12 ) and a second operating rod ( 13 ) are coupled to sleeve piston ( 10 ) at opposite points of the piston ( 10 ). Such an arrangement allows, for example, a first operating rod ( 12 ) to be located above a barrel and a second operating rod ( 13 ) to be located below the barrel. In the alternative, a first operating rod ( 12 ) can be located on the right side of a barrel and a second operating rod ( 13 ) can be located on the left side of the barrel in embodiments of the present invention, such as shown in  FIGS. 16-17 . Similarly, the sleeve parts ( 21 ,  22 ) can be located above and below, or on the right and left sides of, a barrel. 
     Further embodiments of the present invention can provide a barrel that includes a recess or groove longitudinally along the barrel. An operating rod ( 12 ,  13 ,  25 ,  26 ) can be at least partially located in the recess and thereby reduce the distance that the operating rod protrudes beyond the diameter of the barrel. 
     The sleeve piston embodiments described herein, such as the sleeve pistons shown in  FIGS. 1-6 , can provide several advantages over conventional piston-driven systems. Dual operating rods, including symmetrically and/or substantially symmetrically located operating rods, such as those shown in  FIGS. 1-14  and  16 - 17 , can be used to create symmetrical reciprocating mass about a barrel and therefore minimize torque or “muzzle flip,” thereby making a semi- or fully-automatic firearm much easier to control. 
     As understood by one skilled in the art, semi- and fully-automatic firearms can create tremendous and deleterious heat from rapid, yet often necessary, firing. For example, an M-16A2 can rupture its barrel after only 491 rounds, achieving a barrel temperature of around 1600 degrees F.  Fire to Destruction Test of  5.56  M 4A1  Carbine and M 16 A 2  Rifle Barrels, Final Report , Jeff Windham, Small Arms Branch, Engineering Support Directorate, Rock Island Arsenal, September 1996, page 2. This illustrates a non-limiting advantage to fully ventilating the barrel of an auto-loading rifle. 
     The sleeve piston embodiments of the present invention are thus beneficial because they can provide for a lower barrel temperature. First, as shown in  FIGS. 1-14  and  16 - 17 , for example, the first and second operating rods ( 12 ,  13 ,  25 ,  26 ) allow air to fully circulate around the barrel, thereby cooling it. In other words, the first and second operating rods ( 12 ,  13 ,  25 ,  26 ) do not trap hot air against the barrel. Second, the sleeve piston ( 10 ,  20 ) such as the one shown in  FIG. 7  can conduct heat away from the barrel, thereby cooling it. In a conventional piston-driven system such as the AK-47, the piston is offset and thus not in direct or close indirect contact with the barrel. In contrast, the sleeve piston ( 10 ,  20 ) embodiments of the present invention can be in close, if not direct, contact with the barrel as shown in  FIGS. 7-14  and  19  and so can transfer heat directly away from the barrel, thereby cooling it. In other words, the sleeve piston ( 10 ,  20 ) can act like a heat sink for the barrel. As shown in  FIG. 7 , for example, the inner surface of the piston ( 10 ) can be in direct contact with the barrel, facilitating the transfer of heat. The outer surface of the piston ( 10 ,  20 ) can be in contact with the gas block ( 50 ,  60 ,  91 ), also transferring heat away from the barrel. In embodiments where one or more operating rods ( 12 ,  13 ,  25 ,  26 ) are coupled to the sleeve piston ( 10 ,  20 ), such as shown in  FIGS. 7-14 , the one or more operating rods can also act to helpfully transfer heat away from the barrel and into the air due to the high surface area to volume ratio of the operating rods. Accordingly, the sleeve piston embodiments of the present invention, such as those shown in  FIGS. 1-14 ,  16 - 17 , and  19  can fully expose the barrel to air and can also transfer heat away from the barrel to further aid cooling. 
     Further embodiments of the present invention, such as those shown in  FIGS. 7-14  and  19  provide systems for actuating a bolt carrier of a firearm using the sleeve piston embodiments of the present invention. One example of a bolt carrier ( 70 ) useable with embodiments of the present invention is shown in  FIG. 15 . A person of ordinary skill in the art will recognize the bolt carrier ( 70 ) as a bolt carrier from an ARMALITE AR-18/180 modified for use with embodiments of the present invention. Specifically, the bolt carrier ( 70 ) has been modified to include a first strike surface ( 71 ) or lobe and a second strike surface ( 72 ) or lobe. The first strike surface ( 71 ) receives an operating force or push from a first operating rod, such as operating rod ( 12 ), and the second strike surface ( 72 ) receives an operating force or push from a second operating rod, such as operating rod ( 13 ). While the bolt carrier ( 70 ) depicted in  FIG. 15  is based on an ARMALITE AR-18/180 bolt carrier, any suitable bolt carrier can be used with embodiments of the present invention. For example, while the strike surfaces ( 71 ,  72 ) of  FIG. 15  are symmetrically located about the right and left sides of the bolt ( 73 ), the strike surfaces of other embodiments can be located above and below the bolt ( 73 ) in embodiments of the present invention. Similarly, the strike surfaces can be located asymmetrically about a bolt in yet further embodiments of the present invention. For example, both strike surfaces could be located above, or below, the bolt ( 73 ). Of course, for embodiments of the invention that utilize a sleeve piston with a single operating rod, the bolt carrier, such as bolt carrier ( 70 ), can include a single strike surface. By way of a further example, a person skilled in the art will understand that an M-16 bolt carrier could be modified for use with embodiments of the present invention, such as with sleeve piston ( 10 ), by adding strike surfaces like the strike surfaces ( 71 ,  72 ) shown in  FIG. 15  to the left and right sides of the bolt carrier face, for example. 
     As used herein, bolt carrier means includes, but is not limited to, the bolt carrier ( 70 ) structure described with respect to  FIGS. 15-17 . Bolt means also includes, but is not limited to, the bolt ( 73 ) structure described with respect to  FIGS. 15-17 . 
     Returning to the system shown in  FIG. 7 , one embodiment of the present invention provides a monolithic sleeve piston ( 10 ) that can reciprocate along a barrel ( 53 ) to actuate a bolt carrier, such as bolt carrier ( 70 ). A gas block ( 50 ) is coupled to the barrel ( 53 ), wherein the gas block ( 50 ), sleeve piston ( 10 ), and barrel ( 53 ) define a cylindrical gas chamber ( 51 ) that can receive a gas from a fired cartridge. Gas from a fired cartridge is transferred from the barrel ( 53 ) and into the gas chamber ( 51 ) through a gas port ( 52 ), wherein the gas subsequently acts against the face ( 11 ) of the sleeve piston ( 10 ) to thereby move the sleeve piston ( 10 ) rearward to operate a bolt carrier such as bolt carrier ( 70 ).  FIG. 8  provides an additional image showing an arrangement of the sleeve piston ( 10 ), operating rods ( 12 ,  13 ), barrel ( 53 ), and gas block ( 50 ) of  FIG. 7 . 
       FIGS. 9 and 10  show operation of the system of  FIG. 7  after the bullet ( 9 ) from a fired cartridge has passed the gas port ( 52 ).  FIG. 9  shows the moment in time just after the bullet ( 9 ) has passed the gas port ( 52 ). As shown, gas from the fired cartridge travels from the barrel ( 53 ), through the gas port ( 52 ), and into the gas chamber ( 51 ) where it exerts force on the face ( 11 ) of the sleeve piston ( 10 ). The gas in  FIG. 9  has not yet moved the sleeve piston ( 10 ) towards a bolt carrier. 
     The position of the bullet ( 9 ) in  FIG. 10  is for illustrative purposes only and is used to show the system of  FIG. 9  at a point later in time. As understood by a person skilled in the art, the bullet ( 9 ) may be much farther down the barrel ( 53 ), if not having exited the barrel ( 53 ), before the sleeve piston ( 10 ) has moved far enough to pass the gas vent ( 54 ) in a real rifle that implements the system shown in  FIG. 7 . The same illustrative principle is also used for  FIGS. 11-14 . 
     Returning to  FIG. 10 , it can be seen that a gas in the gas chamber ( 51 ) has pushed the sleeve piston ( 10 ) rearward (in the direction of the arrows) towards a bolt carrier, such as bolt carrier ( 70 ). The sleeve piston face ( 11 ) has passed an exhaust port ( 54 ), thereby venting gas from the gas chamber ( 51 ) and rapidly lowering the force exerted by the gas on the sleeve piston ( 10 ). The gas vent ( 54 ) can have any suitable size, shape, and location in embodiments of the present invention. 
       FIGS. 11-14  illustrate systems of additional embodiments of the present invention that include a pseudo- or multi-part sleeve piston ( 20 ). One embodiment as shown in  FIG. 11  provides a sleeve piston ( 20 ) that can reciprocate along a barrel ( 63 ) to actuate a bolt carrier, such as bolt carrier ( 70 ). A gas block ( 60 ) is coupled to the barrel ( 63 ), wherein the gas block ( 60 ), sleeve piston ( 20 ), and barrel ( 63 ) define a gas chamber ( 61 ) that can receive a gas from a fired cartridge. As shown in  FIG. 11 , a gas from a fired cartridge is transferred from the barrel ( 63 ) and into the gas chamber ( 61 ) through a gas port ( 62 ), wherein the gas subsequently acts against the face of each sleeve part ( 23 ,  24 ) to thereby move the sleeve piston ( 20 ) rearward to operate a bolt carrier ( 70 ).  FIG. 12  provides an additional image showing an arrangement of the sleeve piston ( 20 ), operating rods ( 25 ,  26 ), barrel ( 63 ), and gas block ( 60 ) of  FIG. 11 . 
       FIGS. 13 and 14  show operation of the system of  FIG. 11  after the bullet ( 9 ) from a fired cartridge has passed a gas port ( 62 ).  FIG. 13  shows the moment in time just after the bullet ( 9 ) has passed the gas port ( 62 ). As shown in  FIG. 13 , a gas from the fired cartridge travels from the barrel ( 63 ), through the gas port ( 62 ), and into the gas chamber ( 61 ) where it exerts force on the face ( 23 ) of the first sleeve part ( 21 ) and force on the face ( 24 ) of the second sleeve part ( 22 ). The gas in  FIG. 13  has not yet moved the sleeve piston ( 20 ) towards a bolt carrier. 
     As shown in  FIG. 14 , a gas in the gas chamber ( 61 ) has pushed the sleeve piston ( 20 ) rearward (in the direction of the arrows) towards a bolt carrier, such as a bolt carrier ( 70 ). The faces ( 23 ,  24 ) of the sleeve piston ( 20 ) have passed an exhaust port ( 64 ), thereby venting gas from the gas chamber ( 61 ) and rapidly lowering the force exerted by the gas on the first ( 21 ) and second ( 22 ) piston parts. The gas vent ( 64 ) can have any suitable size, shape, and location in embodiments of the present invention. 
     The front of the gas block ( 50 ,  60 ) in further embodiments can comprise a gas block cap that is used to close off the front of the gas block ( 50 ,  60 ). The gas block cap can be detachably coupled to gas block ( 50 ,  60 ) and can be attached using any suitable means, including by using pins, screws, ball detents, and/or threads, and any combination thereof. For example, the gas block cap can be coupled to gas block ( 50 ,  60 ) using threads on the gas block cap and gas block ( 50 ,  60 ). Accordingly, in various embodiments the gas block cap can be removed by unscrewing it from the front of the gas block ( 50 ,  60 ). After the gas block cap is removed from the gas block ( 50 ,  60 ), the sleeve piston ( 10 ,  20 ) and operating rods ( 12 ,  13 ,  25 ,  26 ) can be easily removed through the front of the gas block ( 50 ,  60 ) for inspection, cleaning, and/or replacement. 
       FIG. 19  shows another embodiment of the present invention that provides a monolithic sleeve piston ( 10 ) that can reciprocate along a barrel ( 93 ) to actuate a bolt carrier, such as bolt carrier ( 70 ). A gas block ( 91 ) is coupled to the barrel ( 93 ), wherein the gas block ( 91 ), sleeve piston ( 10 ), and barrel ( 93 ) define a cylindrical gas chamber ( 92 ) that can receive a gas from a fired cartridge. Gas from a fired cartridge is transferred from the barrel ( 93 ) and into the gas chamber ( 92 ) through a gas port ( 94 ), wherein the gas subsequently acts against the face ( 11 ) of the sleeve piston ( 10 ) to thereby move the sleeve piston ( 10 ) rearward to operate a bolt carrier such as bolt carrier ( 70 ). Expansion gases are vented from the gas chamber ( 92 ) by exhaust port ( 95 ). Vent ( 96 ) allows air, water, and/or debris behind the sleeve piston ( 10 ) to exit the gas block ( 91 ) and thereby help ensure reliable operation of the sleeve piston ( 10 ) in adverse conditions. 
     The front of the gas block ( 91 ) and gas chamber ( 92 ) can be closed with a gas block cap ( 97 ). Gas block cap ( 97 ) can be detachably coupled to gas block ( 91 ) and can be attached using any suitable means, including by using pins, screws, ball detents, and/or threads, and any combination thereof. For example, gas block cap ( 97 ) can be coupled to gas block ( 91 ) using threads on gas block cap ( 97 ) and gas block ( 91 ). Accordingly, in one embodiment the gas block cap ( 97 ) can be removed by unscrewing it from the gas block ( 91 ). After the gas block cap ( 97 ) is removed from the gas block ( 91 ), the sleeve piston ( 10 ) and operating rods ( 12 ,  13 ) can be easily removed through the front of the gas block ( 91 ) for inspection, cleaning, and/or replacement. 
     As used herein, gas block means includes, but is not limited to, the gas block structures ( 50 ,  60 ,  91 ) shown and described with regard to  FIGS. 7-14  and  19 . Monolithic gas block means includes, but is not limited to, the gas block structures ( 50 ,  91 ) described with regard to  FIGS. 7-10  and  19 . Pseudo-sleeve gas block means includes, but is not limited to, the gas block structure ( 60 ) described with regard to  FIGS. 11-14 . 
       FIG. 16  illustrates embodiments of the present invention in view of a firearm.  FIG. 16  shows illustrative systems including the sleeve piston ( 10 ) of  FIGS. 1-3 , the sleeve piston systems of  FIGS. 7-10 , and the bolt carrier ( 70 ) of  FIG. 15 . A person skilled in the art will recognize that the receiver ( 80 ,  81 ) carrying bolt carrier ( 70 ) resembles the receiver of an ARMALITE AR-18/180. A person skilled in the art understands however that the embodiments of the present invention are not so limited to the AR-18/180 rifle. For example, lower receiver ( 81 ) of any embodiment of the present invention can comprise a lower receiver that is compatible with an M-16 or AR-10. Similarly, upper receiver ( 80 ) can comprise an M-16- or AR-10-type upper receiver that is compatible with a conventional M-16 or AR-10 lower receiver, respectively. 
     As shown in  FIG. 16 , a spring ( 82 ) over an operating rod ( 12 ) can be used to return the sleeve piston ( 10 ) to battery. Thus in various embodiments where a sleeve piston ( 10 ,  20 ) is coupled to an operating rod ( 12 ,  13 ,  25 ,  26 ) and the piston and rods move independently from a bolt carrier ( 70 ), a mainspring can be used to return the bolt carrier ( 70 ) to battery and a spring ( 82 ) over the operating rod(s) ( 12 ,  13 ,  25 ,  26 ) can be used to return the sleeve piston ( 10 ,  20 ) to battery soon after it transfers its momentum to the bolt carrier ( 70 ). In other embodiments a firearm&#39;s primary recoil spring or mainspring can be used to return the piston to battery, for example, when the bolt carrier ( 70 ), rod(s) ( 12 ,  13 ,  25 ,  26 ) and piston ( 10 ,  20 ) reciprocate as a single unit (as in an AK-47). 
     A rifle ( 90 ) of one embodiment of the present invention is shown in  FIG. 17 , showing the system of  FIG. 16  incorporated into ARMALITE AR-18/180 rifle. As used herein, rifle means includes, but is not limited to, the structures described with respect to  FIG. 17 . As shown in  FIG. 17 , the rifle ( 90 ) of embodiments of the present invention can include, by way of non-limiting example, the sleeve piston systems described with respect to  FIG. 16  including one or more of gas block ( 50 ), sleeve piston ( 10 ), operating rods ( 12 ,  13 ), return spring ( 82 ), bolt carrier ( 70 ), bolt ( 73 ), and barrel ( 53 ). The rifle ( 90 ) can likewise include or utilize the sleeve pistons described with respect to  FIGS. 1-6  and the sleeve piston systems described with respect to  FIGS. 7-14  and  19 . Moreover, the methods of any embodiment of the present invention, including those described with respect to  FIG. 18 , can be used with any of the aforementioned rifles of the present invention. Of course, a person skilled in the art will recognize that the sleeve piston apparatuses, systems, and methods of the present invention are not limited to use with AR-18-type rifles but can be used with any suitable type of rifle, such as M-16-, AR-10-, and AK-47-type rifles. 
     Additional embodiments of the present invention provide methods for actuating or operating a bolt carrier of a firearm using a sleeve piston, wherein the firearm includes a barrel coupled to a receiver, and wherein the bolt carrier is carried by the receiver. One such method for operating the bolt carrier of a firearm is shown in  FIG. 18 . The firearm ( 90 ) can include a barrel ( 53 ,  63 ) coupled to a receiver, with the bolt carrier ( 70 ) carried by the receiver and carrying a bolt ( 73 ). The method can comprise first using ( 101 ) the firearm ( 90 ) to fire a projectile ( 9 ) from a cartridge down the barrel ( 53 ,  63 ,  93 ). Second, a gas from the fired cartridge is directed ( 102 ) against the sleeve piston ( 10 ,  20 ). The sleeve piston can comprise a monolithic sleeve piston ( 10 ) as shown in  FIGS. 1-3 ,  7 - 10 , and  19  for example. The sleeve piston can also comprise, in the alternative, a pseudo-sleeve piston ( 20 ) such as shown in  FIGS. 4-6  and  11 - 14 . One skilled in the art will appreciate that any suitable sleeve piston can be used with the methods of the present invention. 
     The sleeve piston of various methods can use one or more operating rods as shown in  FIGS. 1-14  and  19  to transfer an operating force to a bolt carrier, wherein the bolt carrier includes, but is not limited to, bolt carrier ( 70 ). For example as shown in  FIGS. 1-3 , the sleeve piston ( 10 ) and one or more operating rods ( 12 ,  13 ) can comprise a single piece of metal such as a single piece of cast or milled steel or titanium. In other embodiments the sleeve piston can be detachably coupled from one or more operating rods by means of a fastener such as a screw or pin, for example. In further embodiments the piston can be separate or independent from one or more operating rods so that the sleeve piston and the operating rod(s) can move independently from one another. In one method the sleeve piston and operating rod(s) can be independent but in direct or indirect physical contact when the bolt carrier ( 70 ) is in battery. In further embodiments the sleeve piston can move a predetermined distance before it impacts or transfers force to one or more operating rods, thereby transferring its momentum to and operating a bolt carrier, such as the bolt carrier shown in  FIG. 15 . The bolt carrier and operating rods(s) can be permanently coupled, detachably coupled, or independent in the methods or embodiments of the present invention. 
     Third, the sleeve piston ( 10 ,  20 ) reciprocates or is moved ( 103 ) rearward along the barrel ( 53 ,  63 ,  93 ) in response to the gas. The sleeve piston of any method can be movably received by a gas block ( 50 ,  60 ,  91 ) to define a gas or expansion chamber ( 51 ,  61 ,  92 ). The gas block can be permanently or detachably coupled to a barrel ( 53 ,  63 ,  93 ), or the gas block and barrel can comprise a single unit of manufacture. For example, in one method a sleeve piston ( 10 ) can comprise a circular shape and can reciprocate in a corresponding circular sleeve cylinder gas block to define a gas chamber, such as shown in  FIGS. 7-10  and  19 . In further embodiments, at least a portion of the sleeve piston ( 10 ) can reciprocate on or over an outer cylindrical portion of a gas block to define a gas chamber. The gas block can be detachably coupled to the barrel by a fastener such as by one or more pins or screws, or it can be machined from the barrel itself in embodiments of the invention. One or more gas ports, such as gas port ( 52 ,  94 ), can couple the gas chamber to the barrel in the methods of the present invention. Accordingly, the step of moving ( 103 ) can further comprise the sleeve piston reciprocating or moving in a gas block coupled to a barrel as shown, for example, in  FIGS. 7-14 . 
     Fourth, one or more operating rods ( 12 ,  13 ,  25 ,  26 ) coupled to the sleeve piston ( 10 ,  20 ) push, strike, or transfer ( 104 ) an actuating force to the bolt carrier ( 70 ), thereby moving the bolt carrier ( 70 ) rearward and unlocking the bolt ( 73 ). The sleeve piston of any method can be coupled to a bolt carrier, such as bolt carrier ( 70 ) that reciprocates in a straight light with respect to the barrel. For example, an AR-18/180 ( 70 ), M-16-, or AK-47-type bolt carrier can be used in any method of the present invention. The bolt carrier can include a rotating bolt, such as a seven-lug AR-18 or M-16-type bolt ( 73 ) shown in  FIG. 15 . Any suitable rotating bolt can be used. The one or more operating rods ( 12 ,  13 ,  25 ,  26 ) can contact or strike the bolt carrier ( 70 ) at one or more contact points or lobes ( 71 ,  72 ). For example, in some methods of the present invention a first operating rod ( 12 ) and a second operating rod ( 13 ), such as those shown in  FIGS. 1-6 , can contact the bolt carrier on opposite or substantially opposite points or sides of the bolt carrier ( 70 ) or bolt ( 73 ). 
     Thus, for example, the step of operating ( 104 ) the bolt carrier can comprise operating a bolt carrier ( 70 ) that carries a non-tiling rotating bolt ( 73 ) in embodiments of the present invention. In further embodiments, the step of operating ( 104 ) the bolt carrier can comprise directly pushing, striking, or contacting the bolt carrier with one or more operating rods ( 12 ,  13 ,  25 ,  26 ) such as shown in  FIG. 16 . In further embodiments the one or more operating rods ( 12 ,  13 ,  25 ,  26 ) can indirectly transfer force to the bolt carrier ( 70 ) such as by pushing or striking an intermediate object, such as one or more secondary operating rods situated between the operating rods ( 12 ,  13 ,  25 ,  26 ) and bolt carrier ( 70 ). One skilled in the art will appreciate that the methods can include or be used with any of the apparatus, system, method, and firearm embodiments of the present invention. 
     While the invention has been described in detail in connection with specific embodiments, it should be understood that the invention is not limited to the above-disclosed embodiments. Rather, a person skilled in the art will understand that the invention can be modified to incorporate any number of variations, alternations, substitutions, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Specific embodiments should be taken as exemplary and not limiting.