Patent Publication Number: US-8973483-B2

Title: Gas regulator system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/678,976 filed Aug. 2, 2012 which is hereby incorporated by reference in its entirety. 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/350,156 filed Jan. 13, 2012 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/350,156 claims the benefit of U.S. Provisional Patent Application No. 61/433,115 filed Jan. 14, 2011 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/350,156 claims the benefit of U.S. Provisional Patent Application No. 61/524,138 filed Aug. 16, 2011 which is hereby incorporated by reference in its entirety. 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/348,871 filed Jan. 12, 2012 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/348,871 claims the benefit of U.S. Provisional Patent Application No. 61/433,092 filed Jan. 14, 2011 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/348,871 claims the benefit of U.S. Provisional Patent Application No. 61/433,083 filed Jan. 14, 2011 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/348,871 claims the benefit of U.S. Provisional Patent Application No. 61/478,439 filed Apr. 22, 2011 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/348,871 claims the benefit of U.S. Provisional Patent Application No. 61/479,194, filed Apr. 26, 2011 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/348,871 claims the benefit of U.S. Provisional Patent Application No. 61/498,426, filed Jun. 17, 2011 which is hereby incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 13/348,871 claims the benefit of U.S. Provisional Patent Application No. 61/528,062 filed Aug. 26, 2011 which is hereby incorporated by reference in its entirety. 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/071,990 filed Mar. 25, 2011, which claims the benefit of U.S. Provisional Patent Application No. 61/317,396 filed Mar. 25, 2010, all of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to firearms. The present invention relates more particularly, for example, to methods and systems for increasing the durability and reliability of a firearm, such as to better support sustained fully automatic fire. 
     BACKGROUND 
     Gas operated firearms are well known. Gas operated firearms use some of the gas from a cartridge being fired to extract the spent case of the cartridge and to chamber a new cartridge. The gas travels from a port in the barrel to a gas cylinder where the gas pushes a piston within the gas cylinder to operate a mechanism for extracting the spent case and for chambering the new cartridge. In some firearms, such as the M16 and the M4, the gas cylinder is formed in the bolt carrier and the piston is part of the bolt. In such firearms, gas is provided from the barrel to the gas cylinder by a gas tube. 
     In other firearms, such as the HK416, a separate (not part of the bolt) piston is used. The piston is disposed in a gas cylinder that is not part of the bolt carrier. This separate piston applies force through a tappet or operating rod and a bolt carrier to operate the mechanism for extracting the spent case and for chambering the new cartridge. 
     Whether or not the piston is part of the bolt, it is desirable to prevent gas leakage between the piston and the cylinder. Contemporary gas operated firearms commonly use a plurality of piston rings which fit into a groove of the piston and provide a gas seal between the piston and the cylinder to mitigate gas leakage. For example, the M16, M4, and HK416 use three rings. Each of the rings is a split ring that has a gap formed therein to facilitate installation of the ring and to apply an outward spring force that tends to seal the loose fit between the piston and the cylinder. 
     Contemporary rings possess inherent deficiencies which detract from their overall effectiveness and desirability. For example, the gaps of the three rings occasionally line up in a manner that allows hot gasses to flow readily through the gaps and thereby undesirably bypass the rings. Contemporary gas tubes also possess inherent deficiencies which detract from their effectiveness and desirability. For example, contemporary gas tubes can overheat and lose strength, particularly during sustained fully automatic fire of the firearm. 
     The higher level of heat associated with sustained fully automatic fire can result in undesirable thermal expansion of the gas tube both radially and longitudinally. Such thermal expansion can be substantially beyond an amount accommodated by the available space in the firearm. Such thermal expansion can result in sliding/clearance fits becoming interference fits. That is, a sliding fit can undesirably become a non-sliding fit. When the gas tube heats up excessively, the weakened and expanded gas tube can bend and be damaged, thus causing the firearm to become inoperative. As such, it is desirable to provide methods and systems for mitigating overheating in gas operated firearms. 
     Forward and rearward bouncing of the bolt carrier can cause the cyclic rate of a firearm to increase substantially. This increase in the cyclic rate can reduce the reliability of the firearm and can increase wear on the firearm, as discussed herein. As such, it is desirable to provide methods and systems for mitigating both forward and rearward bouncing of the bolt carrier. 
     The gas port of a contemporary M16/M4 firearm is subject to erosion caused by bullet scrubbing and propellant bombardment. Such erosion results in enlargement of the gas port and consequently an undesirable increase in the cyclic rate of the firearm over time. This undesirable increase in the cyclic rate can eventually result in malfunction and damage to the firearm. As such, it is desirable to provide for the metering of gas in a manner that does not result in an increased cyclic rate over time. 
     BRIEF SUMMARY 
     In accordance with embodiments further described herein, methods and systems are provided for enhancing the reliability of a gas operated firearm, such as a fully automatic gas operated firearm. For example, the gas port of a firearm can be moved forward along the barrel so as to delay the time at which gas acts upon the bolt of the firearm after a cartridge is fired and so as to reduce the pressure of the gas. In this manner, the cyclic rate of the firearm can be reduced and the reliability of the firearm can be enhanced. 
     According to an embodiment, a device can comprise a front sight block for a firearm, a rear band and a front band for attaching the sight block to a barrel of the firearm, and a gas passage formed in either band for facilitating gas flow from the barrel to a gas tube of the firearm. The gas passage can be substantially more forward along the barrel where gas pressure is substantially lower than it would be if formed in the rear band. 
     According to an embodiment, a firearm can comprise a barrel having a gas port, a gas tube and a front sight block for a firearm. The front sight block can have a rear band and a front band for attaching the sight block to the barrel. A gas passage can be formed in the rear band for the long barrel of a rifle and in the front band for the short barrel of a carbine to more nearly match the same operating gas pressure in both firearms. 
     According to an embodiment, a method for making a firearm can comprise forming a gas passage in a front band of a front sight block and forming a gas port in a barrel. The front sight block can be attached to the barrel such that the gas passage is substantially aligned with respect to the gas port. 
     According to an embodiment, a method for operating a firearm can comprise flowing gas from a barrel of the firearm through a front band of a front sight block and to a gas tube. In this manner, the reliability of the firearm can be substantially enhanced. 
     According to an embodiment, a gas regulator block can be configured to mount to a barrel of a firearm. A gas regulator can be disposed substantially within the gas regulator block and can be configured to adjustably vary an amount of gas flow through the gas regulator block. A cover can be configured to cover a portion of the gas regulator block to inhibit inadvertent excessive adjustment of the amount of gas flow and can be configured to uncover the gas regulator screw so it can be removed from the gas regulator block. A gas passage can be formed in the gas regulator block and the gas passage can be configured to communicate gas from the barrel to the gas regulator. 
     According to an embodiment, a system can comprise a firearm having a barrel with a gas port formed therein. A gas regulator block can be mounted to the barrel. A gas regulator can be disposed substantially within the gas regulator block and can be configured to vary an amount of gas flow through the gas regulator block. A cover can be configured to cover a portion of the gas regulator block to inhibit excessive adjustment of the amount of gas flow and can be configured to uncover the portion of the gas regulator block to facilitate removal of the gas regulator screw. A gas passage can be formed in the gas regulator block. The gas passage can be configured to communicate gas from the gas passage to the gas regulator. 
     According to an embodiment, a method can comprise rotating a cover attached to a gas regulator block of a firearm to substantially expose an adjustment screw. The method can further comprise turning the adjustment screw to vary an amount of gas used to cycle the firearm. A spring can urge a plunger into troughs of the adjustment screw to index the adjustment screw as the adjustment screw is turned. 
     The scope of the disclosure is defined by the claims, which are incorporated into this section by reference. A more complete understanding of embodiments will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a bolt showing keyed piston rings exploded therefrom, according to an embodiment; 
         FIG. 2  is an enlarged side view of a piston of  FIG. 1  having one keyed piston ring installed thereon and one keyed piston ring partially installed thereon, according to an embodiment; 
         FIG. 3  is an enlarged perspective view of the piston of  FIG. 1  having two keyed piston rings installed thereon, according to an embodiment; 
         FIG. 4  is a perspective view of a piston showing keyed piston rings exploded therefrom, according to an embodiment; 
         FIG. 5  is an enlarged side view of the piston of  FIG. 4  having one keyed piston ring installed thereon and one keyed piston ring partially installed thereon, according to an embodiment; 
         FIG. 6  is an enlarged perspective view of the piston of  FIG. 4  having two keyed piston rings installed thereon, according to an embodiment; 
         FIG. 7  is a perspective view of a firearm having the bolt of  FIG. 1 , according to an embodiment; 
         FIG. 8  is a perspective view of a firearm having the piston of  FIG. 4 , according to an embodiment; 
         FIG. 9  is a heat dissipating gas tube for a firearm, according to an embodiment; 
         FIG. 10  is a cross-sectional view of a firearm having the heat dissipating gas tube and a gas metering plug, according to an embodiment; 
         FIG. 11  is an enlarged cross-sectional side view of the rear end of the gas tube and a bolt carrier key that receives the rear end of the gas tube, according to an embodiment; and 
         FIG. 12  is a flow chart showing a method for making a firearm having a heat dissipating gas tube, according to an embodiment. 
         FIG. 13  is a top view of a bolt carrier having an anti-bounce assembly, according to an embodiment. 
         FIG. 14  is a side view of the bolt carrier of  FIG. 13 , according to an embodiment. 
         FIG. 15  is an enlarged side view of the anti-bounce assembly of  FIG. 13  showing a double anti-bounce weight in a zero or non-impact position, according to an embodiment. 
         FIG. 16  is an enlarged side view of the anti-bounce assembly of  FIG. 13  showing the double anti-bounce weight in a rearward impact position, according to an embodiment. 
         FIG. 17  is an enlarged side view of the anti-bounce assembly of  FIG. 13  showing the double anti-bounce weight in a forward impact position, according to an embodiment. 
         FIG. 18  is an exploded view of the bolt carrier of  FIG. 13 , according to an embodiment. 
         FIG. 19  is a top exploded view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
         FIG. 20  is a perspective exploded view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
         FIG. 21  is a top assemble view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
         FIG. 22  is a perspective assembled view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
         FIG. 23  is a perspective view of a modified bolt carrier, according to an embodiment. 
         FIG. 24  is an end view of the modified bolt carrier of  FIG. 23 , according to an embodiment. 
         FIG. 25  is a side view of an anvil of  FIG. 23 , according to an embodiment. 
         FIG. 26  is an end view of the modified bolt carrier of  FIG. 23  showing an impact area and a bearing area, according to an embodiment. 
         FIG. 27  is an end view of the modified bolt carrier of  FIG. 23  showing a plunger, according to an embodiment. 
         FIG. 28  includes various views of an anti-bounce assembly, according to an embodiment. 
         FIG. 29  includes various views of a double anti-bounce weight, according to an embodiment. 
         FIG. 30  includes various views of a plunger, according to an embodiment. 
         FIG. 31  includes various views of an anvil, according to an embodiment. 
         FIG. 32  includes various views showing a bolt carrier modification, according to an embodiment. 
         FIG. 33  includes various views showing a bolt carrier modification, according to an embodiment. 
         FIG. 34  includes various views showing a carrier key, according to an embodiment. 
         FIG. 35  shows the front sight block and gas tube of a contemporary firearm, i.e., an M4 carbine. 
         FIG. 36  shows a metering plug installed in a front sight block having the gas port in the standard location and showing the use of a thick wall gas tube, according to an embodiment. 
         FIG. 37  shows a metering plug installed in a front sight block having the gas port moved to a forward location and showing the use of a thick wall gas tube, according to an embodiment. 
         FIG. 38  shows a metering plug installed in a front sight block having the gas port moved to a forward location (with an enlarged view of the installed metering plug) and showing the use of a thick wall gas tube, according to an embodiment. 
         FIG. 39  shows a metering plug installed in a front sight block having the gas port moved to a forward location (with an enlarged view of the uninstalled metering plug and gas tube) and showing the use of a thick wall gas tube, according to an embodiment. 
         FIG. 40  shows a firearm barrel having a gas regulator installed thereon, according to an embodiment. 
         FIG. 41  shows an enlarged view of the gas regulator of  FIG. 40 , according to an embodiment. 
         FIG. 42  shows a cross-sectional view of the gas regulator of  FIG. 40 , according to an embodiment. 
         FIG. 43  shows a cut away view of the gas regulator of  FIG. 40 , according to an embodiment. 
         FIG. 44  shows a partial cross-sectional view of the gas regulator of  FIG. 40 , according to an embodiment. 
         FIG. 45  shows a partial cross-sectional view of the gas regulator of  FIG. 40 , and shows use of a gas flow and sight adjustment tool, according to an embodiment. 
         FIG. 46  shows the gas regulator of  FIG. 40  with the cover rotated, according to an embodiment. 
         FIG. 47  shows a partial cross-sectional view of the gas regulator of  FIG. 40 , according to an embodiment. 
         FIG. 48  shows a partial cross-sectional view of the gas regulator of  FIG. 40 , according to an embodiment. 
         FIG. 49  includes various views of the gas regulator mounted on the barrel, according to an embodiment. 
         FIG. 50  includes various views of the gas regulator, according to an embodiment. 
         FIG. 51  includes various views of the cover, according to an embodiment. 
         FIG. 52  includes various views of the adjustment screw, according to an embodiment. 
     
    
    
     Embodiments of the present invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. 
     DETAILED DESCRIPTION 
     As examples, methods and systems for inhibiting undesirable gas leakage and/or heat build up in a gas operated firearm are disclosed. For example, a pair of rings can be configured to interlock with respect to one another such that the rings rotate within a groove of a piston of a gas system of a firearm. Since the rings rotate in unison, they do not align in a manner that readily facilitates undesirably increased gas flow past the piston. Such rings can generally be used with both M16/M4 and HK416 types of firearms. 
     As a further example, a gas tube that better tolerates the heat associated with sustained fully automatic fire of a firearm is disclosed. The gas tube is less prone to overheating and better accommodates thermal expansion. Thus, the firearm cycles and fires more uniformly and is more reliable. Such a gas tube can generally be used with M16/M4 types of firearms and generally cannot be used with HK416 types of firearms since HK416 types of firearms use a substantially different gas system. 
     As a further example, methods and systems are provided for inhibiting undesirable forward and rearward bouncing of a bolt carrier of a gas operated firearm, such as a fully automatic gas operated firearm. An anti-bounce assembly can mitigate undesirable speeding up of the cyclic rate of a firearm due to gas port erosion and can thus reduce wear and increase the reliability of the firearm. 
     According to an embodiment, the beginning of the gas passage and the barrel gas port can be positioned in the forward ring of a two ring gas regulator block. Forward positioning of the barrel gas port allows a central positioning of the gas regulator screw, surrounding it, and the gas passageway between the gas port and screw with an increased amount of material that is the gas regulator block and the increased amount of material acts as a heat sink, absorbing heat that might otherwise damage the device. 
     According to an embodiment, an adjusting screw can comprise a stem and threads. At least one cutting groove can be formed at an inward end of the threads where the threads join the stem such that the cutting grooves are configured to remove, cut, and/or break up any carbon deposits that may have accumulated in a cavity between an end of the threads and the stem hole in the gas regulator block or in tube configured to extend from the gas regulator block to a bolt carrier assembly of the firearm, such cutting occurring when the screw is adjusted for removal. 
     Examples of embodiments of keyed gas piston rings and pistons/bolts are discussed in detail below. Examples that are suitable for use with the M16/M4 rifle are discussed with reference to  FIGS. 1-3  and  7 . Examples that are suitable for use with the HK416 rifle are discussed with reference to  FIGS. 4-6  and  8 . Examples of embodiments of more heat tolerant and/or heat dissipating gas tubes are also discussed in detail below. Examples of such enhanced gas tubes are discussed with reference to  FIGS. 9-12 . 
     The gas piston of the M16 or M4 is an integrated part of the bolt and a gas cylinder is formed in the bolt carrier. The gas cylinder, i.e., the bolt carrier, moves with respect to the gas piston.  FIGS. 1-3  show a system for inhibiting undesirable gas flow around such a piston and are discussed in detail below. 
       FIG. 1  is a perspective view of a bolt  100  of a gas operated firearm  700  (see  FIG. 7 ), according to an embodiment. The bolt  100  can be a bolt of an M16 rifle, for example. The bolt  100  can have a piston  101  formed thereon. A groove  102  can be formed circumferentially around the piston  101 . A pair of rings  105  are shown exploded from the bolt  100 . The rings  105  can comprise a first ring  105   a  and a second ring  105   b . The rings  105  can be configured to be received at least partially within the groove  102  of the piston  101  of the gas operated firearm  700 . 
     A key  108  can be formed upon each of the rings  105 . The key  108  can extend generally perpendicularly with respect to a plane of the rings  105 . The key  108  can have a generally rectangular cross-section when taken in either of two generally orthogonal planes. 
     A gap  107  can be formed in each of the rings  105 . The gap  107  of each one of the rings  105  can be configured to receive at least a portion of the key  108  of another one of the rings  105 . The gap  107  can have a generally rectangular cross-section when taken in either of two generally orthogonal planes. Thus, a pair of the rings  105  can be configured to interlock with one another such that the two rings  105  can rotate, but can only rotate substantially in unison with respect to one another. 
     In an embodiment, the key  108  and the gap  107  of each ring  105  can be formed such that a pair of the rings  105  are nestable with the key  108  of each of the rings  105  being disposed within the gap  107  of each other of the rings  105  while the rings  105  are substantially flush with respect to one another. The nesting of the rings  105  interlocks the rings  105  such that the rings  105  rotate in unison. 
     In an embodiment, the gaps  107  of the two rings  105  can be diametrically opposed with respect to one another when the rings  105  are interlocked. Since the two rings  105  rotate substantially in unison, the gaps  107  do not align in a fashion that facilitates increased gas flow past the rings  105 . 
     In an embodiment, the rings  105  can be formed of stainless steel. For example, the rings  105  can be formed of 17-4 stainless steel. Various other materials, including refractory materials such as ceramics, are contemplated. 
     In an embodiment, the groove  102  can be substantially rectangular in cross-section. In such an embodiment, the rings  105  can also be substantially rectangular in cross-section and thus can be generally complementary in size and shape with respect to the groove  102 . 
       FIG. 2  is an enlarged side view of the piston  101  having one ring  105   a  fully installed thereon and having one ring  105   b  partially installed thereon, according to an embodiment. The rings  105  can be temporarily bent or spring deformed in order to slide over the piston  101  and into the groove  102 . The key  108  of the second ring  105   b  is positioned to be received at least partially within the gap  107  of the first ring  105   a.    
       FIG. 3  is an enlarged perspective view of the piston  101  having two rings  105  installed thereon, according to an embodiment. The two rings  105  are seated within the groove  102 . The key  108  of the second ring  105   b  is disposed at least partially within the gap  107  of the first ring  105   a  and the key  108  of the first ring  105   a  is disposed at least partially within the gap  107  of the second ring  105   b.    
     A piston  400  of an HK416 is disposed in a gas cylinder  801  of the firearm  800 .  FIGS. 4-6  show a system for inhibiting undesirable gas flow around the piston  400  and are discussed in detail below. 
       FIG. 4  is a perspective view of the piston  400  of a gas operated firearm  800  (see  FIG. 8 ), according to an embodiment. The piston  400  can be a piston of an HK416 rifle, for example. A groove  402  can be formed circumferentially around the piston  400 . A pair of rings  405  are shown exploded from the piston  400 . The rings  405  can comprise a first ring  405   a  and a second ring  405   b . The rings  405  can be configured to be received at least partially within the groove  402 . 
     A key  408  can be formed upon each of the rings  405 . The key  408  can extend generally perpendicularly with respect to a plane of the rings  405 . The key  408  can have a generally rectangular cross-section when taken in either of two generally orthogonal planes. 
     A gap  407  can be formed in each of the rings  405 . The gap  407  of each one of the rings  405  can be configured to receive at least a portion of the key  408  of another one of the rings  405 . The gap  407  can have a generally rectangular cross-section when taken in either of two generally orthogonal planes. Thus, a pair of the rings  405  can be configured to interlock with one another such that the two rings  405  can rotate, but can only rotate substantially in unison with respect to one another. 
     In an embodiment, the key  408  and the gap  407  of each ring  405  can be formed such that a pair of the rings  405  are nestable with the key  408  of each of the rings  405  being disposed at least partially within the gap  407  of each other of the rings  405  while the rings  405  are substantially flush with respect to one another. The nesting of the rings  405  interlocks the rings  405  such that the rings  405  rotate in unison. 
     In an embodiment, the gaps  407  of the two rings  405  can be diametrically opposed with respect to one another when the rings  405  are interlocked. Since the two rings  405  rotate substantially in unison, the gaps  407  do not align in a fashion that facilitates increased gas flow past the rings  405 . 
     In an embodiment, the rings  405  can be formed of stainless steel. For example, the rings  405  can be formed of 17-4 stainless steel. Various other materials, including refractory materials such as ceramics, are contemplated. 
     In an embodiment, the groove  402  can be substantially rectangular in cross-section. In such an embodiment, the rings  405  can also be substantially rectangular in cross-section and thus can be generally complementary in size and shape with respect to the groove  402 . 
       FIG. 5  is an enlarged side view of the piston  400  having one ring  405   a  fully installed thereon and having one ring  405   b  partially installed thereon, according to an embodiment. The rings  405  can be temporarily bent or spring deformed in order to slide over the piston  400  and into the groove  402 . The key  408  of the second ring  405   b  is positioned to be received at least partially within the gap  407  of the first ring  405   a.    
       FIG. 6  is an enlarged perspective view of the piston  400  having two rings  405  installed thereon, according to an embodiment. The two rings  405  are seated within the groove  402 . The key  408  of the second ring  405   b  is disposed at least partially within the gap  407  of the first ring  405   a.    
     According to various embodiments, a device can comprise a first ring  105   a ,  405   a  configured to be at least partially received within a groove  102 ,  402  of a piston  101 ,  400  of a gas operated firearm  700 ,  800 . A second ring  105   b ,  405   b  can be configured to be at least partially received within the groove  102 ,  402 . The first ring  105   a ,  405   a  and second ring  105   b ,  405   b  can be configured to interlock with one another such that the first ring  105   a ,  405   a  and second ring  105   b ,  405   b  rotate substantially in unison within the groove  102 ,  402 . Various means for effecting such interlocking are contemplated. The use of a key  108 ,  408  and a gap  107 ,  407  as discussed herein are by way of example only, and not by way of limitation. 
     Any desired number of rings  105 ,  405  and any desired number of grooves  102 ,  402  in the piston  101 ,  400  may be used. For example, two grooves  102 ,  402 , each having two rings  105 ,  405  or three rings  105 ,  405  apiece may be used. Thus, various embodiments may comprise 2, 3, 4, 5, 6, or more rings  105 ,  405 . 
     In various embodiments, the gaps  107 ,  407  can be partial gaps that do not extend entirely though the rings  105 ,  405 . For example, the gaps  107 ,  407  can be sufficiently sized to receive at least a portion of the keys  108 ,  408  while not forming a separation in the rings  105 ,  405 . Thus, the gaps  107 ,  407  may be depressions, indentations, or cutouts, for example. Any desired number and configuration of the gaps  107 ,  407  and the keys  108 ,  408  can be used. The gaps  107 ,  407  and the keys  108 ,  408  can be generally complementary with respect to one another. The gaps  107 ,  407  and the keys  108 ,  408  can be non-complementary with respect to one another. 
     The piston rings  105 ,  405  need not be received within a groove  102 ,  402  of the piston  101 ,  400 . Rather, the piston rings  105 ,  405  can be placed upon the piston  101 ,  400  and can be held in position by any means or structure desired. The piston rings  105 ,  405  can cooperate with the piston  101 ,  400  to mitigate gas leakage past the piston  101 ,  400 . 
       FIG. 7  is a perspective view of a firearm  700  having the piston  101  (see  FIG. 1 ) formed on a bolt  100 , according to an embodiment. The firearm  700  can be an M16 or an M4, for example. The firearm  700  can have one or more pairs of rings  105  disposed about the piston  101  thereof to mitigate gas leakage past the piston  101 , as discussed herein. 
       FIG. 8  is a perspective view of a firearm  800  having the piston  400  (see  FIG. 4 ), according to an embodiment. The firearm  800  can be an HK416, for example. The firearm  800  can have one or more pairs of rings  405  disposed about the piston  400  thereof to mitigate gas leakage past the piston  400 , as discussed herein. 
     In operation, a shooter fires the firearm  700 ,  800  and hot, high pressure gas is provided by the cartridge. For an M16 or M4 type of rifle, the gas travels through a front sight  750  to the gas tube  705 , then through the gas tube  705  and a bolt carrier key  752  to the bolt carrier  702 , where the gas moves the bolt carrier  702 , and consequently the bolt  100 , so as to effect extraction of the spent cartridge and chambering of a new cartridge. The bolt  100  is disposed within a cylinder  701  formed in the bolt carrier  702 . For an HK416 type of rifle, the gas moves the piston  400  within the gas cylinder  801  so as to move a tappet or operating rod  802  to effect extraction of a spent cartridge and chambering of a new cartridge. 
     In either instance, the use of rings  105 ,  405  having gaps  107 ,  407  and keys  108 ,  408  that facilitate nesting or interlocking of the rings  105 ,  405  substantially mitigates undesirable gas flow past the piston  101 ,  400 . The nested or interlocked rings  105 ,  405  provide increased resistance to such gas flow by preventing the gaps  107 ,  407  from aligning with respect to one another. For example, gas can be substantially forced to follow a longer and more contorted path under the rings  105 ,  405  from which the gas reemerges to flow past the piston  101 ,  400 . This longer and more contorted path around four corners substantially inhibits such gas flow and consequently inhibits gas leakage past the piston  101 ,  400 . 
     Firearms  700  that have the piston  101  formed on the bolt  100  thereof can be referred to herein as M16/M4&#39;s, or M16/M4 types of firearms, or members of an M16/M4 family of firearms. Firearms  800  that do not have the piston  101  formed on the bolt  100  thereof can be referred to herein as HK416&#39;s, HK416 types of firearms, or members of an HK416 family of firearms. 
     Thus, according to one or more embodiments, two rings can be nested such that undesirable gas leakage past the piston is substantially inhibited. In this manner, damage to the rings can be substantially mitigated and fouling of components of the firearm, such as within the receiver thereof, can be substantially mitigated. By inhibiting gas leakage past the piston, reliability of the firearm is substantially enhanced and operation of the firearm is made more uniform. 
     Some gas operated firearms use a contemporary gas tube to deliver high pressure, very hot, gas to the piston  101  formed upon the bolt  100 , as discussed herein. The M16 and the M4 are examples of firearms  700  that deliver gas to the piston  101  formed upon the bolt  100  via a contemporary gas tube. When the firearm  700  is shot repeatedly over an extended length of time, such as during extended fully automatic fire using a plurality of high capacity magazines, the contemporary gas tube can heat up. In such instances, the temperature of the contemporary gas tube can be excessive and thus undesirable damage to the contemporary gas tube can result. When the gas tube heats up, the length and/or diameter of the gas tube can increase substantially due to thermal expansion. Such thermal expansion can interrupt the firing cycle of the firearm and thus result in the firearm becoming inoperative. As such, it is desirable to provide methods and systems for mitigating heat build up and for accommodating thermal expansion of gas tubes in gas operated firearms. 
     A heat dissipating gas tube  705  can have enhanced heat dissipation such that during extended fully automatic fire the gas tube  705  can remain at a sufficiently low temperature as to not incur substantial damage. An example of such a gas tube  705  is discussed below with reference to  FIGS. 9-12 , according to one or more embodiments. 
     According to one or more embodiments, a gas tube  705  provides enhanced heat dissipation and/or enhanced heat accommodation, as discussed with reference to  FIGS. 9-12 . The enhanced heat dissipation tends to inhibit overheating of the gas tube  705 . The enhanced heat accommodation tends to allow the gas tube  705  to continue to function properly when heated, particularly when heated by sustained fully automatic fire. 
       FIG. 9  is the gas tube  705  for an M16 and/or M4 type of firearm  700 , according to an embodiment. The gas tube  705  can have a heat dissipater formed thereon. For example, the gas tube  705  can have threads  707  formed upon a substantial portion of the length of the gas tube  705 . 
     Other examples of heat dissipaters can include fins, fingers, and any other structures that tend to increase the surface area of the gas tube  705  and thus enhance radiation of heat from the gas tube  705 . A plurality of spaced apart annular fins can substantially encircle the gas tube  705 , for example. A plurality of longitudinal fins can extend along a length of the gas tube  705 , for example. A spiral fin can extend around a length of the gas tube  705 , for example. 
     The outer diameter and/or the inner diameter of the gas tube  705  can be increased to enhance the ability of the gas tube  705  to operate under extended fully automatic fire. For example, in one embodiment, the outer diameter of the gas tube  705  or a portion of the gas tube  705  can be increased from the standard 0.180 inch to approximately 0.218 inch. 
     According to an embodiment, the threads  707  can be ¼-32 UNEF (Unified National Extra Fine) threads, for example. Various other types of the threads  707  are contemplated. More than one type of the threads  707  can be used. Any desired combination of the threads  707  or types of the threads  707  can be used. In one embodiment, the threads  707  can extend along a portion of the length of the gas tube  705 . For example, the threads  707  can extend along a portion of the gas tube  705  that is away from ends,  721  and  722 , of the gas tube  705 . Thus, the ends  721  and  722  of the gas tube  705  can have no threads  707  formed thereon. In one embodiment, the threads  707  can extend along the entire gas tube  705 . 
     The threads  707  need not be conventional threads. The threads  707  need not be any type of standard threads, e.g., threads made according to an accepted standard. The threads  707  can be formed with a die. The threads  707  can be formed by machining. The threads  707  can be formed by any desired method. 
     The threads  707  can be integral with the gas tube  705 . The threads  707  can be formed separately from the gas tube  705  and/or can be attached to the tube  705 . The threads  707  can be formed of either the same material as the gas tube  705  or can be formed of a different material with respect to the gas tube  705 . 
     In one embodiment, the threads  707  can be solely for heat dissipation. In one embodiment, the threads  707  can have another use other than heat dissipation. For example, the threads  707  can be used to mount the gas tube  705  to the firearm  700 . Thus, at least one end of the gas tube  705  can screw into a threaded opening on the firearm  700 . 
     The gas tube  705  can be configured to attach to a contemporary firearm  700 . For example, the gas tube  705  can have a first bend  711  and a second bend  712  formed therein to facilitate mounting of the gas tube  705  to a contemporary firearm  700 . The first bend  711  and a second bend  712  can align the forward end and the rearward end of the gas tube  705  with their respective connections to the firearm  700 . A bead  725  can be formed on the reward end of the tube  705  to facilitate a desired fit into the bolt carrier key  752  ( FIGS. 10 and 11 ) of the firearm  700 . 
     In one embodiment, the gas tube  705  can be formed of stainless steel. For example, the gas tube  705  can be formed of 347 stainless steel. In one embodiment, the gas tube  705  can be formed of a refractory material, such as a ceramic material. 
     The gas tube  705 , and more particularly the threads  707 , can have any desired finish. For example, various textures, coatings, and treatments that enhance heat dissipation are contemplated. 
       FIG. 10  is a cross-sectional side view of a firearm  700  having the gas tube  705 , according to an embodiment. The gas tube  705  and/or the rings  105  (see  FIGS. 1-3 ) can be provided as a kit for upgrading contemporary firearms such as the M16 and M4. Thus, the gas tube  705  and the rings  105  can be provided and installed together. Such upgrading can be performed in the field, at an armory, or at a maintenance depot. The gas tube  705  and/or the rings  105  can be changed together. Either the gas tube  705  or the rings  105  can be changed alone (without changing the other). Thus, the gas tube  705  and the rings  105  can be changed or used independently with respect to one another. 
     In operation, a shooter fires the firearm  700 ,  800  and hot, high pressure gas is provided by the cartridge. For an M16 or M4 type of rifle, the gas travels through a front sight  750  to the gas tube  705 , then through the gas tube  705  and the bolt carrier key  752  to the bolt carrier  702 , where the gas moves the bolt carrier  702 , and consequently the bolt  100 , so as to effect extraction of the spent cartridge and chambering of a new cartridge. The bolt  100  is disposed within a cylinder  701  formed in the bolt carrier  702 . During sustained fully automatic fire, the gas tube  705  is exposed to a substantial quantity of hot gases from the fired cartridges. According to an embodiment, the threads  707  provide increase surface area for radiating this heat so that the temperature of the gas tube  705  can be maintained within an acceptable range. 
     As the gas tube  705  heats ups, it expands both in length and diameter. According to an embodiment, the length, Dimension M, of the gas tube is sufficiently short so as to accommodate thermal expansion of the gas tube  705  in length without causing the firearm  700  to malfunction. According to an embodiment, the diameter, Dimension N, of the gas tube  705  is sufficiently small so as to accommodate thermal expansion of the gas tube  705  in diameter, particularly at the bolt carrier key  752  interface thereof, without causing the firearm  700  to malfunction. 
     Contemporary M16/M4 firearms have a gas tube  705  with a plug at the front end of the gas tube  705 . However, the plug of contemporary M16/M4 firearms does not substantially restrict gas flow. Contemporary M16/M4 firearms rely upon the gas port  1003  formed in the barrel to perform a gas metering function. The gas port  1003  is subject to erosion and thus suffers from substantial disadvantages with regard to this metering function. 
     More particularly, the M16 and M4 use the gas port  1003  diameter as the means to control the amount of gas flow. However, the forward corner of the gas port  1003  intersection with barrel bore is eroded from its original sharp corner into an enlarging triangle by the scrubbing of each passing bullet and the bombardment of propellant grains. This erosion of the gas port  1003  causes the gas flow therethrough to increase over time. As the gas flow increases, the gun cycle speeds up, undesirably resulting in feed jams, extraction failures, and/or carrier bounce. Misfires begin and grow worse over time until the gun cripples itself from excessively worn and/or broken parts. 
     To mitigate the undesirable effects of gas port erosion, a gas metering plug  1001  can be installed in the front end of the gas tube  705 . The gas metering plug  1001  can have a gas metering hole  1002  that the gas from the barrel must flow through before entering the gas tube  705 . According to an embodiment, the gas metering hole  1002  is out of reach of bullet scrubbing and the impact of propellant grains. The gas metering plug  1001  can be made of a heat resistant material, so that it remains substantially unchanged by any amount of firing. According to an embodiment, the gas metering hole  1002  is always smaller than the hole of the gas port  1003  (such that the gas metering hole  1002  always performs a gas metering function). 
     Thus, although the gas port  1003  continues to erode so that the gas flow that reaches the metering hole  1002  continues to increase in pressure, the gas metering hole  1002  meters the gas and thus mitigates the undesirable effects of gas port erosion so as to the extend the useful life of the gun. 
       FIG. 11  is an enlarged cross-sectional side view of a forward end of the bolt carrier key  752  of  FIG. 10 . The rearward end or bead  725  of the gas tube  705  is received within the bolt carrier key  752 . When a contemporary gas tube expands in length, such as due to the heat of sustained fully automatic fire, it may bottom out or interfere within the bolt carrier key  752 , such that the gas tube bends undesirably due to such expansion. Such bottoming out and/or bending can inhibit uniform cycling or otherwise prevent desired operation of the firearm  700 . 
     According to an embodiment, the gas tube  705  can be shorter in length, Dimension M of  FIG. 9 , such that additional or desirable clearance, Dimension T, is provided between the bead  725  and any portions of the bolt carrier key  752  that the bead  725  can bottom out or interfere with during such expansion. Thus, the likelihood of such bottoming out or interference is substantially mitigated. 
     According to an embodiment, the bead  725  can have a reduced diameter, Dimension N of  FIG. 9 , such that expansion of the diameter thereof is less likely to cause the bead  725  to interfere, bind and/or not move freely within the bolt carrier key  752 . Thus, undesirable binding of the gas tube  705  within the bolt carrier key  752  can be substantially mitigated. Such binding can undesirably increase the likelihood of the gas tube  705  bending and/or the firearm  700  malfunctioning. 
     According to an embodiment, the gas tube  705  can be shorter in length, Dimension M and the bead  725  can have a reduced diameter, Dimension N. Thus, undesirable interferences can be mitigated and uniformity of cycling can be enhanced and a more reliable firearm can be provided. 
       FIG. 12  is a flow chart showing a method for making a firearm  700  having the gas tube  705 , according to an embodiment. The method can comprise cutting a piece of ¼ OD×0.065 wall, stainless steel tubing, for example, to a desired length as shown in block  1101 . For example, the tubing can be cut to a length of approximately 9.668 inches. The tubing can be cut with a tubing cutter or a saw, for example. 
     The method can further comprise forming threads  707  upon the cut tubing, as indicated in block  1102 . For example, ¼-32 threads can be formed upon a section of tubing having a diameter of approximately 0.250 inch. The threads  707  can be formed with a lathe or with a die, for example. 
     The method can further comprise forming a first bend  711  in the tubing, as indicated in block  1103 . A second bend  712  can be formed in the tubing, as indicated in block  1104  to define the gas tube  705 . The first bend  711  and the second bend  712  can be formed consecutively or simultaneously. The first bend  711  and the second bend  712  can be formed using a fixture, jig, or tubing bend, for example. 
     The gas tube  705  can be installed in a firearm  700  as indicated in block  1105 . For example, the gas tube  705  can be installed in an M16 or an M4 type of firearm  700 . The bead  725  can be formed on the reward end of the tube  705  to facilitate a desired fit into a gas block interface of the firearm  700 . The bead  725  can be formed at any desired point in the fabrication process. For example, the bead  725  can be formed either before or after the threads  707  are formed. 
     Referring again to  FIG. 9 , the gas tube  705  can comprise a gas tube retention hole  751  that is used to pin (attach) the tube to the front sight  750 . According to an embodiment, the length, Dimension M, of the gas tube  705  from the center of the gas tube retention hole  751  to the rear end of the gas tube  705  and/or the rear end diameter, dimension N, of the bead  725  can be approximately the same as for a contemporary gas tube for an M16 and/or M4. For example, Dimension M can be approximately 9.600 inches for an M4 and can be approximately 14.98 inches for an M16. For example, Dimension N can be approximately 0.180 inch. Thus, in one or more embodiments the gas tube  705  can readily replace the contemporary gas tube of an M16 and/or M4. 
     According to an embodiment, the length, Dimension M, and/or the rear end diameter, Dimension N, of the bead  725  can be less than for a contemporary gas tube for an M16 and/or M4. For example, Dimension M can be less than 9.570 inches for an M4 and can be less than 14.95 inches for an M16. For example, Dimension N can be less than 0.1792 inch diameter. Thus, the gas tube  705  can be approximately 0.100 inch shorter and can have an outer diameter of approximately 0.001 inch less at the rear end, i.e., the bead  725 , as compared to a standard gas tube for the same firearm. One or more embodiments can fit within the bolt carrier key  752  of an M16 and/or M4 and can readily replace contemporary gas tubes. The shorter length, Dimension M, and the smaller outer diameter, Dimension N, can better accommodate thermal expansion, such as can be caused by using larger capacity magazines. Thus, the gas tube  705  can have further enhanced heat resistance. 
     According to an embodiment, the outer diameter, Dimension Q, of a portion of the gas tube  705  at the rear end thereof can be approximately 0.171 inch. The diameter, Dimension P, of the gas tube  705  can be 0.186 inch. 
     The dimensions of the gas tube  705 , as well as the configuration thereof, including any bends therein, can be whatever is necessary to fit a particular firearm. More or less than two bends can be used. Thus, the gas tube  705  can have any desired shape and configuration. 
     One or more embodiments can provide a replacement for contemporary gas tubes. Such embodiments are less prone to overheating and less likely to malfunction due to heat induced weakness and/or heat induced thermal expansion, particularly during sustained fully automatic fire of the firearm  700 . Thus, the firearm  700  can cycle and fire more uniformly and can be substantially more reliable. 
     One or more embodiments can provide a replacement for contemporary gas tubes that can withstand the heat of firing at least as well as other components of the firearm. Thus, a failure or problem with the gas tube will be substantially less likely to be the cause of a malfunction of the firearm. 
     One or more embodiments can be used in various different gas operated rifles, carbines, pistols, and the like. Although embodiments are discussed herein with respect to the M16/M4 and HK416, such discussion is by way of illustration only and not by way of limitation. Various embodiments can be used with various gas operated firearms, including rifles, carbines, and pistols. 
     As those skilled in the art will appreciate, the M16 service rifle and the M4 carbine have a variety of reliability shortcomings. According to various embodiments, methods and systems are provided for inhibiting undesirable forward and rearward bouncing of a bolt carrier of a gas operated firearm, such as an M16 and/or an M4. These methods and systems can be used in combination with other methods and systems described herein to mitigate at least some of these shortcomings. For example, a drop in replacement kit can be provided to address at least some of these shortcomings. 
     An often neglected problem in gas operated firearms is gas port erosion. Gas port erosion causes the gas port to become larger, which allows more gas to be used and thus gradually speeds up the gun cycle. Speeding up the gun cycle can cause feed jams, failures to extract, and carrier bounce misfires. It can also increase wear on the firearm and reduce accuracy during use of the firearm. 
     The M4 carbine has more trouble with gas port erosion than the M16 rifle, even though both of these firearms use the same bolt carrier group. The M4&#39;s gas port location is closer to the chamber, where gas port erosion is more aggressive. Because of gas port erosion, the M4&#39;s unlocking cam can begin to unlock too early in the fires cycle and thus can cause the firearm&#39;s bolt to break at the lugs or cam pin hole. This typically doe not occur in the M16 rifle and typically does not occur in new M4s. It generally only occurs in M4s that have fired enough to substantially erode the gas port. In addition to reliability problems, the resulting high rate of fire makes the gun less controllable on full auto, wastes ammunition, and intensifies heat problems. 
     Anticipating that 60-shot and perhaps even 100-shot magazines may soon replace the current standard 30-shot M16/M4 magazines, the consequent heat problems associated with such increased capacity (and the resulting extended rapid firing of the firearm) also need to be addressed. The M4 gas tubes can soften and bend (and thus become inoperable) in as few as four 100-shot bursts. The M16 gas piston rings can burn out in as few as two 100-shot bursts. To mitigate such heat problems, the piston rings and thick wall threaded gas tube may be used, as discussed herein. 
       FIG. 13  is a top view of a bolt carrier having a longer dwell and an anti-bounce assembly, according to an embodiment. To prevent broken bolts, a double cut cam can have a 0.062 longer dwell  1301  (also shown in  FIGS. 18 ,  23 ,  28 ,  32 ,  33 ) than the standard cam, before the unlocking cam surface  3301  (see  FIG. 33 ) begins to rotate the bolt to its unlocked position. This longer dwell at least partially compensates for the time differences between the M16 unlocking start and the early start of the M4 due to its rearward gas port location. The force on the locking lugs causing them to bind is thus reduced to the same resistance as in the M16 rifle, so that the cause of broken bolts is substantially eliminated. 
     A single cut cam of the same new length with 0.062 longer dwell would have the same timing advantage, but the double cut has two additional advantages. The helix portion of the cam has wider clearance for dust and dirt. Although the unlocking earn surface  3301  has 0.062 longer time dwell, the cam pin and bolt head location on the locking side have the same starting location as the original cam so that the bolt head overtravels beyond the bolt holdopen device by the same amount giving the holdopen enough time to rise into position. 
     To mitigate the effect of gas port erosion and higher rate of fire (excessive cycle speed) three compatible but separate features can be used. First, the M16 and M4 use the gas port hole diameter as the means to control the amount of gas flow, but the forward corner of that gas port intersection with barrel bore can become eroded from its original sharp corner into an enlarging triangle caused by the scrubbing of each passing bullet and the bombardment of propellant grains. As gas flow increases, the gun cycle speeds up, feed jams, extraction failure, misfires begin and grow steadily worse until the gun cripples itself with worn or broken parts. To reduce this undesirable effect, a plug can be installed in the end of the gas tube and the plug can have a metering hole that the gas must flow through. Thus, the metering of gas flow is out of reach of bullet scrubbing and impact of propellant grains and is made of heat resistant material, so that the meter hole is unchanged by any amount of firing. Although the gas port hole continues to erode so that the gas flow that reaches the metering hole continues to increase in pressure, the metering hole (which can be configured such that it is always smaller than the gas port hole), reduces the effect of gas port erosion (not entirely, but significantly), to extend the useful life of the gun. 
     Second, it is not surprising that gas port erosion speeds up the firearm cycle, because the bolt group is thrown more vigorously to the rear. However, it is important to also appreciate that the forward cycle of the bolt group also undesirably speeds up. Faster forward movement is caused by bolt carrier bounce as the buffer and carrier impact the rear wall. The buffer doesn&#39;t bounce, but carrier does. If rear carrier bounce can be eliminated, then approximately half the rate of fire gain can be eliminated. 
     For example, assume that the cyclic rate of fire of a new M4 is 800 shots per minute and that the firearm has fired enough rounds to erode the gas port sufficiently to speed up the cyclic rate to 1000 shots per minute. This represents an increase of 200 shots per minute in the cyclic rate. If that increase were cut in half, the gain would only be 100 shots per minute. Thus, the firearm would have a cyclic rate of 900 shots per minute instead of 1000 shots per minute and the useful life of the firearm would be substantially extended. 
     When the bolt group begins to move forward slowly, it starts to push the top cartridge in the magazine forward, so that this cartridge enters the feed ramp at a slow speed and is smoothly cammed upward into the chamber opening. By way of contrast, if the bolt group bounces forward at high speed, then the bullet point hits the feed ramp (which is 7° steeper in the M4 than in the M16) at high speed. The bullet tends to bounce higher as the cyclic rate increase. When the cyclic rate increases sufficiently, the bullet will miss the chamber opening and jams the gun. Although this commonly occurs with contemporary 30-shot magazines, high capacity magazine provided by SureFire, LLC of Fountain Valley, Calif. are designed to feed reliably at a very wide range of cyclic rates. 
     Referring to  FIGS. 13-18 ,  23 , and  28 , a combination rate reducer and anti-bounce assembly, referred to herein as anti-bounce assembly  1305 , can be mounted in the rear tubular section  1350  common to a M16 and M4 bolt carrier  1300 , according to an embodiment. The only modification needed to be made to the bolt carrier  1300  is a vertical cut or slot  1352  faulted through the left side wall of the bolt carrier  1300  as shown in  FIG. 26 . 
     The anti-bounce assembly  1305  can comprise of a steel cylinder or weight  1400  having two cavities  1501  and  1502  formed therein. Within each cavity  1501 ,  1502 , a first spring  1511  and a second spring  1512  can be disposed. The first spring  1511  can be disposed in cavity  1501  upon a first plunger  1521  and the second spring  1512  can be disposed in cavity  1502  upon a second plunger  1522 . The first plunger  1521  and the second plunger  1522  can be substantially hollow. The weight  1400  can be free to slide within the bolt carrier  1300  and can be biased centrally by the first spring  1511  and the second spring  1512 , as discussed herein. 
     As shown in  FIG. 18 , a central cavity  1801  can be formed between the two cavities  1501  and  1502 . The central cavity  1801  can define a continuous passage between the two cavities  1501  and  1502 . 
     The two plungers  1521  and  1522  can extend through corresponding openings  1821  and  1822  (see  FIG. 18 ) into the central cavity  1801 . By inserting the anti-bound assembly  1305  into the tubular section  1350  of the bolt carrier  1300 , then placing a flat anvil  1351  through a slot  1352  in the bolt carrier  1300  and on into the central cavity  1801 , and then inserting a retaining pin  1861  through the hollow plungers  1521 ,  1522  and a hole  1862  in the anvil  1351 , the anti-bounce assembly  1305  can be secured within the bolt carrier  1300 . 
     The weight  1400  can have the two cavities  1501  and  1502 , as well as the central cavity  1801  formed therein. The weight  1400  can slide fore and aft within the tubular portion  1350  of the bolt carrier  1300 . The springs  1511  and  1512  can tend to center the weight  1400 . The dimensions of the central cavity  1801  can allow the weight  1400  to move fore and aft approximately 0.10 inches, for example, before the weight  1400  impacts the anvil  1351 . Such motion is resisted in either direction by the force of each spring  1511 ,  1512  and by the fact that each plunger  1521 ,  1522  has a travel limiting stop  1900  (see  FIG. 19 ) formed thereon. Thus, when inertia drives the weight  1400  forward to strike the anvil  1351 , then only the rearward spring  1512  is compressed (as shown in  FIG. 17 ), while the forward spring  1511  and plunger  1521  move away from the anvil  1351  and the opposite occurs when the weight  1400  move rearward (as shown in  FIG. 16 ). In that way, the springs  1511  and  1512  are preloaded and biased to hold the weight  1400  in mid position, e.g., approximately centered (as shown in  FIG. 15 ) within its limits of travel. 
     When the bolt carrier  1300  impacts going forward and tries to bounce rearward the weight  1400  impacts forward again (as shown in  FIG. 17 ) and vice-versa (as shown in  FIG. 16 ). Thus, the weight  1400  partially defines an anti-bounce device in both directions, not just in the forward direction. Since the anti-bounce assembly  1305  mitigates rearward bounce, it is also a rate reducer (it tends to reduce the cyclic rate of a firearm). According to one or more embodiments, the anti-bounce assembly  1305  can be a semi-permanent installation, meaning that it can be removed (by driving the retaining pin into the forward plunger) or it can remain in place since the firing pin, cam pin, and bolt standard disassembly can be done with the device installed. 
       FIG. 34  includes various views showing a carrier key  3400 , according to an embodiment. The use of a 0.500 inch shorter carrier key  3400 , buffer, and main spring stack height increases the bolt carrier  1300  allowable travel about 13% and reduces the rate of fire to about 80% of what it otherwise is. Except for the design of the key  3400 , the only change to the carrier  1300  can be that two number 8 screw holes are replaced with a single 10-32 screw hole. 
     Although this alone does not necessarily reduce parts wear, it can increase full auto controllability and hit probability, conserve ammunition and reduce heat buildup. Thus, operation and reliability can be enhanced. 
     The use of such a carrier key  3400  can comply and work normally without the shortened buffer. It can therefore be offered to create the option to use a shortened buffer and spring stack for a reduced rate of fire. 
       FIG. 19  is a top exploded view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
       FIG. 20  is a perspective exploded view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
       FIG. 21  is a top assemble view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
       FIG. 22  is a perspective assembled view of the plungers, springs, and double anti-bounce weight of  FIG. 18 , according to an embodiment. 
       FIG. 24  is an end view of the modified bolt carrier of  FIG. 23 , according to an embodiment. 
       FIG. 25  is a side view of an anvil of  FIG. 23 , according to an embodiment. 
       FIG. 26  is an end view of the modified bolt carrier of  FIG. 23  showing an impact area and a bearing area, according to an embodiment. 
       FIG. 27  is an end view of the modified bolt carrier of  FIG. 23  showing a plunger, according to an embodiment. 
       FIG. 29  includes various views of a double anti-bounce, according to an embodiment. 
       FIG. 30  includes various views of a plunger, according to an embodiment. 
       FIG. 31  includes various views of an anvil, according to an embodiment. 
       FIG. 32  includes various views showing a bolt carrier modification, according to an embodiment. 
       FIG. 33  includes various views showing a bolt carrier modification, according to an embodiment. 
       FIG. 34  includes various views showing a carrier key as discussed herein, according to an embodiment. 
     Referring now to  FIGS. 35-39 , a rearwardly positioned gas port  3506  of a contemporary M16/M4 type of firearm can be moved forward, away from the receiver, so as to increase the time between firing a cartridge and cycling the bolt of the firearm and so as to reduce the pressure used to cycle the firearm. The cyclic rate of the firearm can be reduced and stress on components of the firearm can be reduced. In this manner the reliability of the firearm can be substantially enhanced, as discussed herein.  FIGS. 35 and 36  show the rearwardly positioned gas port  3506  as it is positioned in a contemporary M4 firearm.  FIG. 36  additionally shows the use of a metering block  3601 , according to an embodiment.  FIGS. 37-39  show the gas port  3703  moved forward as well as the use of the metering block  3601 , according to an embodiment. 
     With particular reference to  FIG. 35 , the front sight block (also know as a gas block or forging)  3501  and gas tube  3502  of a contemporary firearm, i.e., an M4 carbine, are shown. Firearms of the M16/M4 family are constructed such that the rearwardly positioned gas port  3506  of the barrel  3507  is located proximate the rear band  3504  of the sight block  3501 . Gas from the barrel  3507  passes through the rearwardly positioned gas port  3506  and through a gas passage  3503  in the rear band  3504  to reach the gas tube  3502 . 
     With particular reference to  FIG. 36 , a metering block  3601  (better shown in  FIGS. 38 and 39  and which can be the same as or similar to metering plug  1001 ) can be installed in the front sight block  3501 , according to an embodiment. The metering block  3601  can be installed in a firearm that has the gas port  3506  in the standard location, i.e., proximate the rear band  3504 . A thick wall gas tube  3510  can additional be used, according to an embodiment. 
     With reference to  FIGS. 37-39 , the gas port  3703  can be located further forward as compared to that of a contemporary firearm, according to an embodiment. The thick wall gas tube  3510  can be used. The metering block  3601  can be disposed within the front sight block  3501 , such as within that portion of the thick wall gas tube  3510  that is received within the front sight block  3501 . 
     The gas port  3703  can be re-located to this more forward position without moving or changing the shape of the front sight block  3501  or the rear  3504  and front  3505  bands, which surround the barrel  3507  to attach the front sight block  3501  to the barrel  3507 . The gas passage  3702  is drilled in the front band  3505  instead of in the rear band  3504 . Clearance  3810  can be provided in the lower portion of the front band  3505  either prior to such drilling or by the drilling process itself so as to facilitate such drilling. 
     The rear band  3504  and the front band  3505  can be formed integrally with the front sight block  3501  (as a single forging or casting, for example). Alternatively, the rear band  3504  and the front band  3505  can be formed separately with respect to the front sight block  3501 . 
     The gas port  3506  ( FIG. 35 ) of a contemporary firearm was originally located in the rear band  3504  when the front sight block  3501  was designed for the longer barrel of the M16 rifle. Then, the same front sight block  3501  and the rearwardly positioned gas port  3506  configuration was used for the 5½ inch shorter carbine barrel. In the carbine, the front sight block  3501  was moved rearward 5½ inches (with respect to the rifle) to maintain the standard distance from the bayonet lug to the muzzle. The rearwardly positioned gas port  3506  was also moved rearward 5½ inches. 
     The distance from bullet start (firing) to the gas port determines the available pressure and the distance from gas port to the muzzle determines the time that pressure is available, thus the ratio between the two distances determines the impulse (force multiplied by time) of the gas system for the gun. The ratio for an 18½ inch bullet travel length of the rifle barrel is 63/37 (63% from the bullet start to the gas port and 37% from the gas port to the muzzle). The ratio for the 13 inch bullet travel length of the carbine barrel is 47/53. Since the ratio used for the rifle barrel proved to be reliable over decades of service, this reliability suggests that the distance from bullet start to the gas port used on the carbine barrel is two inches shorter than necessary to maintain the same ratio as the rifle. It thus indicates that the gas port is much closer to the firing chamber (bullet start position) in contemporary M16/M4 firearms than it needs to be. 
     Placing the gas port  3506  closer to the chamber causes the gas port  3506  ( FIG. 35 ) to be subjected to higher pressure and temperature than necessary. This is because the closer the gas port  3506  is to the chamber, the higher the temperature and pressure to which the gas port  3506  is exposed. Higher temperatures and pressures undesirably cause more aggressive gas port erosion. Additionally, as the carbine&#39;s gas system starts unlocking the bolt while there is higher pressure in the chamber (compared to the rifle), the bolt&#39;s cam pin hole and locking lugs are undesirably subjected to more stress, which can cause them wear prematurely, bind, and ultimately fail. 
     Without changing the external dimensions of the front sight block  3501  (these dimensions need to remain the same to accommodate the bayonet, tripod, barrel launched grenade and separate grenade launcher) a full two inch correction isn&#39;t feasible. However, it is feasible to reposition the gas port 1.23 inches further forward as discussed herein, thus gaining substantial benefit. Thus, by moving the barrel&#39;s gas port and the gas block&#39;s passageway hole from the rear band 1.23 inches forward into the front band  3505 , problems associated with contemporary firearms can be substantially mitigated. 
     A bore  3712  can be formed in the front sight block  3501  for receiving the gas tube  3510 . The bore  3712  can extend completely through the front sight block  3501 . 
     As best shown in  FIGS. 38 and 39 , the metering block  3601  can comprise an inlet  3804  ( FIG. 39 ) and a bore  3801 . The inlet  3804  and/or the bore  3801  are sized and configured to provide the desire gas metering function. That is, the inlet  3804 , the bore  3801 , or both are configured to allow a desired amount of gas to flow from the gas port  3703  to the gas tube  3510 . The inlet  3804  and/or the bore  3801  can define a fixed, calibrated orifice for determining the amount of gas flow through the metering block  3601 . Thus, the amount of gas used to cycle the firearm can be better controlled, e.g., can be fine tuned. 
     An opening  3803  ( FIG. 39 ) can be formed in the gas tube  3791  to facilitate gas flow from the gas passage  3702  to the metering block  3601 . A hole  3802  can be provided through the metering block  3601  and/or the gas tube  3510  to facilitate attachment, e.g., pinning, of the gas tube  3510  and/or the metering block  3601  to the front sight block  3501 . 
     As discussed herein, gas operated firearms utilize an operating cycle that is powered by high temperature and high pressure gas produced by the combustion of propellant from a fired cartridge. A small portion of this gas is tapped through a hole or gas port in the barrel and is diverted through a passage or tube to push on a piston and thereby cause internal parts, e.g., a bolt carrier assembly, of the firearm move rearward according to a multi-stepped operating cycle. The gas actuation phase of the operating cycle is short compared to the overall length of the operating cycle. Thus, adequate rearward movement of the internal parts of the firearm is somewhat dependent on inertia. A spring that is compressed by the parts as they move rearward returns the parts to their original forward position. 
     In general, to provide reliable operation, the gas flow in a gas operated firearm should be regulated to provide an operating cycle of the firearm that is within a certain or optimal range, e.g., a range of operating cycle speeds. If the operating cycle is too slow (such as when there is insufficient gas flow), then a rearward part of the operating cycle may fail to be completed and the firearm may not be ready to fire again when needed. 
     If the operating cycle is too fast (such as when there is excessive gas flow), then even more types of malfunctions can occur as compared to when the operating cycle is too slow. High speed cycling can cause malfunctions, excessive wear, or can make the firearm inoperative. For example, the firearm can jam at an inopportune time, such as during battlefield use. 
     When properly designed and new, a gas operated firearm&#39;s gas flow is typically properly regulated for reliable function. Thus, a new gas operated firearm generally cycles within a speed range that is appropriate for reliable operation. Generally, no adjustment to the gas flow is needed for a properly designed, new gas operated firearm. 
     However, the high temperature and high pressure operating gas from fired cartridges is erosive by nature. Grains of still burning propellant add to the erosion. As the gas flows through the internal passages inside of the firearm to provide power for the operating cycle, the gas wears down metal surfaces, rounding sharp corners and/or eroding depressions into the metal. The closer surfaces are to the source of heat and pressure, e.g., the chamber, the greater this erosive effect. 
     Also, rapid successive firing heats the barrel, thereby weakening the steel and making it even more susceptible to gas erosion. Recently, reliable, high capacity magazines (such as SureFire  60  and  100  round magazines) have become widely available, thus allowing unprecedented amounts of ammunition to be fired though such firearms in a short time. Such rapid firing tends to compound the detrimental effects of gas erosion. 
     Eroded gas passages tend to allow the gas to flow more readily therethrough. This increases the volume of gas passing through the system, thereby undesirably speeding up the operating cycle. As the erosion continues to increase, so does the operating cycle speed of the gas operated firearm. 
     When sped up, moving parts of the gas operated firearm may no longer function as intended. A component of the firearm may bounce off of angled surfaces that the component should cause to move, or may bounce off of surfaces that the component should stop against, thus causing timing related malfunctions. 
     It is known in the art that when the speed of a moving mass is doubled, its impact force increases by 400%. As these moving components strike harder and harder against their stopping surfaces, then battering, breakage, and recoil increases. Also, the centerline of the barrel is thrown more violently upwards during firing so as to ruin aiming of the firearm and thus causes ammunition to be wasted. 
     Thus, as a gas operated firearm undergoes more use; the likelihood of needing an adjustment to the gas flow becomes more likely. If such an adjustment is not made, then the firearm is likely to malfunction eventually. 
     Referring now to  FIGS. 40-52 , a gas regulator system for a firearm  5000  ( FIG. 43 ) is shown, according to an embodiment. The gas regulator system is suitable for use with gas operated firearms, such as the M16 rifle and M4 carbine. The gas regulator system can be adapted for use with other gas operated firearms. 
     With particular reference to  FIGS. 40-43 , the gas regulator system can comprise a gas regulator block  5101  that can be mounted to a barrel  5102  of the firearm  5000 . A gas regulator  5103  can comprise an adjustment screw  5106  that at least partially defines a needle valve  5107 . The adjustment screw  5106  can have a hexagonal head  5141 . A gas passage  5104  formed in the gas regulator block  5101  can receive combustion gas from a fired cartridge via gas port  5123  of the barrel  5102 . A plug  5114  can redirect or deflect the gas from a generally upward (and partially rearward) direction to a generally rearward direction and into a gas tube  5113 . The tube  5113  can have has a wall thickness of between 0.045 inch and 0.063 inch. A slanted surface  5116  can be formed on the plug  5114  to enhance the deflection of the gas from the gas port  5104  into the tube  5113 . A cross pin  5117  can attach the gas regulator block  5101 , the plug  5114 , and the tube  5113  together. 
     The adjustment screw  5106  can comprise a threaded portion  5109  having detents or troughs  5108  (better shown in  FIG. 52 ) formed therein. A plunger  5111  can be biased downwardly by a spring  5112  to engage the troughs  5108 . The spring  5112  and the plunger  5111  can be slidably disposed out side of the gas regulator block  5101 , such as within a tower  5140  that extends next to the gas regulator block  5101 . 
     According to an embodiment, the adjusting screw  5106  can comprise a stem  5151 . The stem  5151  can extend beyond the threaded portion  5109 . At least one cutting groove  5152  can be formed at an inward end of the threaded portion  5109  where the threaded portion  5109  joins the stem  5151 . The cutting grooves  5152  can be configured to remove carbon deposits that have accumulated in a cavity or a tube, e.g., the tube  5113 , which is configured to extend from the gas regulator block to a bolt carrier assembly of the firearm. The cavity can be formed between an end of the threaded portion  5109  and a stem hole in the gas regulator block  5101 . The cutting can occur when the adjusting screw  5106  is adjusted for removal. 
     A cover  5118  can cover the adjustment screw  5106 . The cover  5118  can be rotatably attached to the gas regulator block  5101  via a post  5119 . The cover  5118  can be held onto the post  5119  via a snap ring  5121 . The cover  5118  can be held in the closed position, wherein the cover  5118  covers the adjustment screw  5106 , via a hook  5122  ( FIGS. 48 and 51 ) that engages a portion of the gas regulator block  5101  and via the cross pin  5117 . The cross pin  5117  can be received within a hole  5130  formed in the cover  5118  and can be pushed into the gas regulator block  5101  to allow the hook  5122  to disengage the gas regulator block  5101  and to allow the cover  5118  to rotate and thus expose the adjustment screw  5106 . 
     According to an embodiment, the size, shape, and location of the gas regulator block  5101  can be substantially maintained with respect to a contemporary gas regulator block. In this manner, commonly available parts and accessories such as bipods, bayonets, and grenade launchers can be used with the disclosed gas regulator block  5101 . Surfaces on the gas regulator block  5101  may or may not be used as the front sight mounting system. For example, the gas regulator block  5101  can comprise a front sight  5201 . The front sight  5201  can be adjustable for bullet drop compensation. 
     According to an embodiment, a gas system that resists erosion, manages heat buildup, as well as provides more accurate and safer operation, is provided. Adjustable regulation of the gas system as it erodes is also provided, thereby allowing the operator to desirably maintain control over the operating speed of the weapon. 
     According to an embodiment, more effective heat management is provided by the gas regulator block  5101 , which is mounted on the barrel  5102  of the gas operated firearm  5000 . The gas port  5123  leading from the barrel  5102  into the gas regulator block  5101  can be moved as far forward in the gas regulator block  5101  as practical. Operating gas closer to the front of the barrel  5102  (and thus further from the chamber where combustion of the propellant mostly occurs), is lower and more consistent in pressure and temperature. The gas which flows through a more forward located gas passage  5104  will cause less erosion and will tend to provide a more consistent operating cycle. For example, a more consistent operating cycle time can be provided. 
     Besides being moved forward, the gas passage  5104  in the gas regulator block  5101  can be drilled at a rearward angle to help smooth the gas flow as it turns sharply into the gas tube  5113 . The tube  5113  can be a thin wall metal tube mounted at least partially within the gas regulator block  5101 , as discussed herein. When the gas reaches the tube  5113 , it can be diverted rearward, by the plug  5114 . The plug  5114  can be permanently mounted in the tube  5113 , for example. One or more surfaces  5116  formed on the plug  5114  can be shaped to enhance gas flow rearward, from the gas passage  5104  into the tube  5113 . The cross pin  5117  can extend through the gas regulator block  5101 , through the tube  5113 , and through the plug  5114 , so as to hold the gas regulator block  5101 , the tube  5113 , and the plug  5114  together. 
     According to an embodiment, operating gas is routed from the barrel  5102  and through the gas regulator block  5101 . The tube  5113  can extend behind the gas regulator block  5101 , to conduct the gas rearward, to the bolt carrier assembly where the gas unlocks and moves the bolt and bolt carrier. 
     By moving the gas passage  5104  forward, the area of the gas regulator block  5101  surrounding the thin wall gas tube  5113  is lengthened. This area is also wider and taller. The resulting greater mass provides a larger heat sink for the tube  5113 . The larger heat sink better cools the hot gases from fired cartridges. If desired, heat radiating fins could be formed in this area on the outside of the gas regulator block  5101  to further draw heat away from the tube  5113 . Keeping the tube  5113  from over-heating during rapid firing is important. Heat has been known to warp gas tubes to the point of failure. Thus, the gas regulator system can both regulate the amount of gas and can cool the gas so as to provide more reliable operation of the firearm, maintain a desired cyclic rate of the firearm, and prevent damage to the firearm. 
     Proximate the center of the gas regulator block  5101  and intersecting the tube  5113  can be the gas regulator adjustment screw  5106 . The gas regulator adjustment screw  5106  partially defines and functions as the needle valve  5107 . By screwing the adjustment screw  5106  in and out, the tip of the adjustment screw  5106  affects the flow of operating gas flowing through the tube  5113 . Screwing the adjustment screw  5106  to the full forward position tends to block all gas flow. Screwing the adjustment screw  5106  out to its rear stop can provide more gas flow than would ever be needed. The adjustment screw  5106  can be made of heat resistant material and/or can be coated with heat resistant material. The adjustment screw  5106  can be a hexagonal driving head screw, although other configurations can be used. 
     Rotational movement of the gas adjustment screw  5106  can be controlled or limited by a spring tensioned detent. For example, indexing troughs  5108  can be formed in the threaded portion  5109  of the screw  5106  and the plunger  5111  can apply force, via the spring  5112 , to these troughs  5108  to facilitate accurate adjustment of the screw  5106  and to inhibit unintended rotation of the screw  5106 . Accurate adjustment of the screw  5106  can be provided by counting the clicks caused by the plunger  5111  as the plunger  5111  sequentially engages the troughs  5108  when the screw  5106  is turned. Counting the clicks from full engagement (a fully screwed in position) of the screw  5106  can provide an indication of how far out the screw  5106  has been turned and how much gas can be expected to flow, for example. 
     This stepped, incremental adjustment of the gas regulator  5103  can allow the user to reduce the operating cycle speed of the firearm  5000  back down to a correct rate as erosion of the gas port  5123  speeds up the operating cycle. The firearm  5000  can also be tuned via the screw  5106  to function correctly with ammunition loaded to different power levels, e.g., with different powder loads and/or bullet weights. 
     Adjustment can also be made when the weapon is fired with a sound suppression device attached to the barrel  5102  to account for the difference in gas pressure within the barrel  5102  caused by the sound suppression device. The use of a sound suppression device is known to speed up the operating cycle of a firearm due to the increase of pressure with the barrel  5102  caused thereby. 
     When the firearm  5000  operates at the lowest speed, e.g., the longest operating cycle, that still provides correct functioning of the firearm  5000 , then recoil force is at its lowest. Shot to shot firing is optimized, as the barrel does not tend to rise above the line of sight as much during recoil, thereby making rapid fire more accurate. This serves to conserve ammunition, reduce heat, and reduce wear on the whole weapon system (which can include auxiliary devices such as laser sights, flashlights, grenade launchers, and the like). 
     The spring  5112  provided for detent tension of the plunger  5111  in the troughs  5108  of the screw  5106  can be mounted at the far side of a long plunger  5111 , as remotely as practical from the gas regulator adjustment screw  5106 . The plunger  5111  and spring  5112  can be mounted within the projecting tower  5140 , such as along side of the gas regulator block  5101 . Such mounting can inhibit the intense heat generated by rapid fire shooting from transferring into the spring  5112 , which could cause the spring  5112  to lose some or all of its spring tension. 
     To correctly adjust the gas regulator  5103 , the adjustment screw  5106  of the needle valve  5107  should be screwed all the way inward, then a magazine loaded with one round of the desired ammunition can be installed in the firearm  5000  and the gun fired semi auto. Then the screw  5106  can be unscrewed one click after each one of several successive shots are fired (each time with a single round in the magazine) until the weapon&#39;s last round device catches the bolt. The screw  5106  can be unscrewed two more clicks (to assure adequate gas flow), where it can remain with the gun cycling correctly until gas port erosion, a change in ammunition, or some other factor causes the gas regulator to require readjustment. 
     Outboard of the screw  5106  can be a cover  5118 . The cover  5118  can allows the screw  5106  to be accessible for adjustment, but can also limit how far the screw  5106  can be backed out of the gas regulator block  5101 , so that the screw  5106  can always maintain adequate thread engagement during firing to keep it safely engaged with the gas regulator block  5101 . 
     The gas regulator cover  5118  can be held securely in place on the gas regulator block  5101 . At the rear the cover  5118  can be held on the post  5119  by the snap ring  5121 . At the front the cover  5118  can be held by an interlocking hook  5122  and cross pin  5117 . The hook  5122  can be disengaged by rotating the cover  5118 . The cover  5118  can rotate about the centerline of the post  5119  and the snap ring  5121 . The cover  5118  cannot be readily rotated out of the way. 
     The same cross pin  5117  that holds the gas tube  5113  into the gas regulator block  5101  must be partially driven inward to allow the cover  5118  to be rotated up and thereby expose the adjusting screw  5106 . Thus, the operator can adjust the gas flow (to vary the operating cycle speed), but can not easily remove the cover  5118  from the gas regulator block  5101 . Removing the cover  5118  allows the gas regulator screw  5106  to be removed from the gas regulator block  5101 , if need be. 
     According to an embodiment, the gas regulator block  5101  can include features that act as a front sight, similar to that of the contemporary M16 rifle and M4 carbine. The sight protection ears  5502  on the gas regulator block  5101  have been raised. Features have also been made so that the staff of the front sight  5201  and an adjustment plunger  5503  can move more deeply downwards. By installing a taller staff of the front sight  5201 , a higher line of sight can be attained. This was done to provide an improvement in the M16 Rifles and M4 Carbines with Picatinney flat top rails over the receiver with a detachable receiver mounted carrying handle. The standard detachable handle has inadequate clearance under it for a hand to pass through it. With a higher front sight and rear sight adjusted higher, a detachable carry handle with correct handle height for hand clearance can be installed. 
     With particular reference to  FIG. 45 , a wrench or tool  5200  can be provided. The tool  5200  can be used to both adjust gas flow and adjust bullet drop for the front sight  5201 . 
     Embodiments described above illustrate, but do not limit, the invention. It should also be understood that numerous modifications and variations are possible in accordance with the principles of the present invention. Accordingly, the scope of the invention is defined only by the following claims.