Patent Publication Number: US-9404707-B2

Title: Air gun with gas spring assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 14/299,321, filed on Jun. 9, 2014. 
    
    
     TECHNICAL FIELD 
     The disclosure generally relates to an air gun, and more specifically to a gas spring assembly for an air gun. 
     BACKGROUND 
     An air gun is a rifle, pistol, etc., which utilizes a compressed gas to fire a projectile. Air guns may be powered by, for example, a coil spring assembly or a gas spring assembly. 
     Air guns typically include a compression tube that defines a compression chamber, and is attached to a trigger assembly. A barrel is attached to the compression tube and is in fluid communication with the compression chamber. When powered by a coil spring assembly, the coil spring assembly is housed within the compression chamber of the rifle. The coil spring assembly includes a coil spring coupled to a piston. Cocking the gun moves the piston, which compresses the coil spring until a latch on the rear of the piston engages a sear on the trigger assembly. Actuating the trigger assembly releases the sear of the trigger assembly and allows the coil spring to decompress, pushing the piston forward, and thereby compressing the gas, i.e., air, in the compression chamber directly behind the projectile. Once the air pressure rises to a level sufficient to overcome any static friction between the projectile and the barrel, the projectile moves forward within the barrel, propelled by an expanding column of gas. 
     The coil spring assembly permits use of a center, i.e., an in-line latch, wherein the piston includes a rod that extends along a central, longitudinal axis of the piston. The rod includes the latch which is generally in-line and concentric with a longitudinal axis of the piston. Accordingly, the sear engages the latch substantially in-line with the longitudinal axis of the piston, instead of off-line, radially spaced from the longitudinal axis of the piston, adjacent an outer radial wall of the piston. Such an in-line latching system reduces torque in the spring assembly, which increases the efficiency of the spring assembly and the power of the air gun. 
     When the air gun is powered by a gas spring assembly, the gas spring assembly is housed within the compression chamber of the rifle. The gas spring assembly includes a piston that defines a sealed interior pressure chamber disposed within the piston. The interior pressure chamber contains a gas, such as air or nitrogen. The piston is slideably disposed over a rod. Cocking the gun moves the piston over the rod, such that the rod displaces the gas within the interior pressure chamber, thereby compressing the gas within the interior pressure chamber, until the latch on the rear of the piston engages the sear on the trigger assembly. Actuating the trigger assembly releases the sear of the trigger assembly and allows the gas spring assembly to decompress, pushing the piston forward, and thereby compressing the gas, i.e., air, in the compression chamber directly behind the projectile. Because the rod is disposed concentric with the piston about the longitudinal axis of the piston, it is difficult to configure an air gun including both an in-line latching system and a gas spring assembly. 
     SUMMARY 
     A gas spring assembly for an air gun is provided. The gas spring assembly includes a piston that defines an interior pressure chamber, and includes an annular wall extending along a longitudinal axis between a rearward end and a forward end. The piston includes an end wall disposed adjacent the forward end of the annular wall, and a latch bushing attached to and disposed adjacent the rearward end of the annular wall. The latch bushing defines a central bore that extends along the longitudinal axis. A guide rod is slideably supported within the central bore of the latch bushing. The piston is axially moveable along the longitudinal axis relative to the guide rod, between a compressed position and an un-compressed position. The guide rod includes a first end for engaging a trigger assembly in abutting engagement. The latch bushing includes a ledge that is operable to engage a sear of the trigger assembly in latching engagement when the piston is disposed in the compressed position and the sear is disposed in a cocked position. 
     The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the teachings when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross sectional view of an air gun, from a first side, showing a gas spring assembly having a piston disposed in an un-compressed position, with a latch bushing of the gas spring assembly de-latched from a sear of a trigger assembly. 
         FIG. 2  is a schematic cross sectional view of the air gun, from the first side, showing the piston in a compressed position, with a latch bushing of the gas spring assembly latched to the sear of the trigger assembly. 
         FIG. 3  is a schematic, enlarged, fragmentary cross sectional view of the air gun, from above, showing a guide rod of the gas spring assembly abutting the trigger assembly. 
         FIG. 4  is a schematic cross sectional view of the latch bushing of the gas spring assembly. 
         FIG. 5  is a schematic plan view of the latch bushing. 
         FIG. 6  is a schematic, enlarged, fragmentary cross sectional view of the air gun, from above, showing a charging valve system of the gas spring assembly. 
         FIG. 7  is a schematic exploded cross sectional view of the piston of the gas spring assembly showing the charging valve system. 
         FIG. 8  is a fragmentary, schematic cross section view of an alternative embodiment of the air gun, from the first side. 
         FIG. 9  is a fragmentary, schematic cross section view of another alternative embodiment of the air gun, from the first side. 
     
    
    
     DETAILED DESCRIPTION 
     Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” “top,” “bottom,” etc., are used descriptively for the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims. Furthermore, the teachings may be described herein in terms of functional and/or logical block components and/or various processing steps. It should be realized that such block components may be comprised of any number of hardware, software, and/or firmware components configured to perform the specified functions. 
     Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an air gun is generally shown at  20 . The air gun  20  includes a stock (not shown), a trigger housing  22  supporting a trigger assembly  24 , a compression tube  25  supporting a gas spring assembly  26 , and a breech block  27  supporting a barrel  28 . The compression tube  25  is attached to the trigger housing  22 . The breech block  27  is disposed adjacent the compression tube  25 . Preferably, the barrel is press fit into or otherwise attached to the breech block  27 . The air gun  20  utilizes a burst of compressed air to fire a projectile  30 . The air gun  20  shown in  FIGS. 1 and 2  may be described as a break barrel style air gun  20 . However, it should be appreciated that the teachings of the disclosure may be incorporated into other styles of air guns, such as but not limited to a fixed barrel style air guns. 
     Referring to  FIGS. 1 and 2 , the compression tube  25  defines a compression chamber  32 , with the gas spring assembly  26  disposed within the compression chamber  32 . The compression chamber  32  is in fluid communication with the barrel  28 . The breech block  27  and the barrel  28  are pivotable relative to the compression tube  25  about a shaft  34 , between a firing position and a cocking position as is well known. A lever  36  interconnects the breech block  27  and the gas spring assembly  26 . Movement of the breech block  27  and barrel  28  from the firing position into the cocking position moves the lever  36 , which in turn moves the gas spring assembly  26  from an un-compressed position, shown in  FIG. 1 , into a compressed position, shown in  FIG. 2 , thereby compressing the gas within the gas spring assembly  26 . Movement of the breech block  27  and the barrel  28  from the firing position into the cocking position also moves the trigger assembly  24  from a de-cocked position, shown in  FIG. 1 , into a cocked position, shown in  FIG. 2 , and latches the trigger assembly  24  to the gas spring assembly  26 . Once the barrel  28  is moved back into the firing position, the air gun  20  is ready to fire. 
     When the trigger assembly  24  is disposed in the cocked position, with the gas spring assembly  26  disposed in the compressed position, actuation of the trigger assembly  24  releases the gas spring assembly  26 , which allows the gas spring assembly  26  to decompress. Decompression of the gas spring assembly  26  compresses the air contained within the compression chamber  32 , which fires the projectile  30 . 
     The trigger assembly  24  is housed within and supported by the trigger housing  22 . As noted above, the trigger assembly  24  is moveable between the cocked position and the de-cocked position. The cocked position is generally associated with a ready to fire position, and the de-cocked position is generally associated with a post firing, i.e., not-ready to fire position. The trigger assembly  24  may include any trigger assembly  24  commonly known and utilized to fire a weapon. Typically, the trigger assembly  24  includes a housing  38  that supports a trigger  40  and a sear  42 . The trigger  40  is engaged to operate the sear  42  through a mechanical connection. However, it should be appreciated that the trigger assembly  24  may be configured in some other manner. When engaged, the sear  42  mechanically latches the gas spring assembly  26  in the compressed position. 
     Referring to  FIGS. 1 and 2 , the gas spring assembly  26  includes a piston  44  and a guide rod  46 . The piston  44  includes an annular wall  48 , a latch bushing  50 , and an end wall  52 . The guide rod  46  and the piston  44 , including the latch bushing  50 , the annular wall  48 , and the end wall  52 , are co-axially and concentrically disposed relative to each other about a longitudinal axis  54 . The end wall  52  may include a seal  53  for radially sealing between an outer radial surface of the end wall  52  and an inner radial surface of the compression tube  25 . The seal  53  is operable to seal the compression chamber  32  between the end wall  52  and the compression tube  25 , while stationary and while the piston  44  is moving relative to the guide rod  46 . The seal  53  may include, but is not limited to, a rubber O-ring or other similar device. 
     The latch bushing  50  may be, but is not required to be, fixedly attached to the annular wall  48  of the piston  44 . The piston  44  and the latch bushing  50  are slideably disposed over and moveable along the longitudinal axis  54  relative to the guide rod  46 . The guide rod  46  is disposed in abutting engagement with the trigger assembly  24 , and remains positionally fixed along the longitudinal axis  54  relative to the trigger assembly  24 , with the piston  44  and the latch bushing  50  moving relative to the guide rod  46 . As noted above, the piston  44  is moveable between the compressed position and the un-compressed position. 
     The piston  44  defines an interior pressure chamber  56 . The interior pressure chamber  56  is bounded by and defined by the annular wall  48 , the end wall  52 , and the latch bushing  50 . The gas spring assembly  26  includes a pressurized gas, such as air or nitrogen, which is disposed within the interior pressure chamber  56  of the piston  44 . The gas spring assembly  26  is configured for compressing the pressurized gas within the interior pressure chamber  56  of the piston  44 , in response to movement of the piston  44  from the un-compressed position into the compressed position. 
     As the piston  44  moves axially along the longitudinal axis  54  relative to the guide rod  46 , from the un-compressed position into the compressed position, the piston  44  moves over the guide rod  46  thereby positioning a larger portion of the guide rod  46  within the interior pressure chamber  56 . Increasing the volume of the guide rod  46  disposed within the interior pressure chamber  56  decreases the volume within the interior pressure chamber  56  available for the gas disposed within the interior pressure chamber  56 , thereby compressing the gas and increasing a fluid pressure of the gas within the interior pressure chamber  56 . Compression of the gas within the interior pressure chamber  56  loads the gas spring assembly  26  in preparation for firing the projectile  30  when actuated by the trigger assembly  24 . 
     As noted above, the piston  44  includes the annular wall  48 , the end wall  52 , and the latch bushing  50 . The annular wall  48  extends a length along the longitudinal axis  54 , between a rearward end  58  and a forward end  60 . The rearward end  58  is disposed nearer a butt end of the stock than is the forward end  60 , and the forward end  60  is disposed nearer a muzzle of the barrel  28  than is the rearward end  58 . The annular wall  48  is disposed annularly about the longitudinal axis  54 , and defines a radial outer boundary of the interior pressure chamber  56 . The end wall  52  is disposed adjacent the forward end  60  of the annular wall  48 , and defines a forward axial boundary of the interior pressure chamber  56 . The latch bushing  50  is disposed adjacent the rearward end  58  of the annular wall  48 , opposite of the end wall  52  along the longitudinal axis  54 , and defines a rearward axial boundary of the interior pressure chamber  56 . 
     The latch bushing  50  defines a central bore  62 , which extends axially along and is concentric with the longitudinal axis  54 . The latch bushing  50  is fixedly attached to the annular wall  48  of the piston  44 . The latch bushing  50  may be attached to the annular wall  48  in any suitable manner, such as through a threaded connection. Alternatively, the latch bushing  50  may be held in place between a pair of snap rings or other similar devices that are secured to the annular wall  48  of the piston  44  and prevent axial movement of the latch bushing  50  along the longitudinal axis  54  relative to the annular wall  48 . 
     The guide rod  46  is slideably supported within the central bore  62  of the latch bushing  50 . The piston  44 , including the annular wall  48 , the latch bushing  50  and the end wall  52 , is axially moveable along the longitudinal axis  54  relative to the guide rod  46 , between the un-compressed position shown in  FIG. 1 , and a compressed position shown in  FIG. 2 . 
     The guide rod  46  includes a first end  64  and a second end  66 . The first end  64  is disposed rearward of the second end  66 , and engages the housing  38  of the trigger assembly  24  in abutting engagement. The second end  66  of the guide rod  46  is disposed within the interior pressure chamber  56  of the piston  44 . The guide rod  46  includes a shank portion  68  and a head portion  70 . The shank portion  68  includes the first end  64 , and extends axially along the longitudinal axis  54 . The head portion  70  is disposed at the forward end  60  of the guide rod  46 , within the interior pressure chamber  56 . The shank portion  68  defines a first diameter  72 , and the head portion  70  defines a second diameter  74 . The second diameter  74  of the head portion  70  is larger than the first diameter  72  of the shank portion  68 . The pressurized gas disposed within the interior pressure chamber  56  biases against the head portion  70  of the guide rod  46 , i.e., the second end  66  of the guide rod  46 , to bias the second end  66  of the guide rod  46  toward the rearward end  58  of the piston  44 . The head portion  70 , disposed at the second end  66  of the guide, contacts an interior surface of the latch bushing  50  and prevents the pressurized gas within the interior pressure chamber  56  from completely displacing the guide rod  46  from the central bore  62  of the latch bushing  50 . 
     The first diameter  72  of shank portion  68  of the guide rod  46  is substantially equal to a bore diameter of the central bore  62  of the latch bushing  50 . However, it should be appreciated that the bore diameter of the central bore  62  of the latch bushing  50  will be slightly larger than the first diameter  72  of the shank portion  68  to provide sufficient clearance to allow relative movement of the latch bushing  50  over the guide rod  46 . However, the clearance between the central bore  62  of the latch bushing  50  and the shank portion  68  of the guide rod  46  should be minimized so that the latch bushing  50  may radially support the guide rod  46 . 
     The latch bushing  50  includes a bushing length  76  measured along the longitudinal axis  54 . The latch bushing  50  radially supports the guide rod  46  along the entire bushing length  76  of the latch bushing  50 . Radially supporting the guide rod  46  along the entire bushing length  76  of the latch bushing  50  reduces relative flexure or bending between the piston  44  and the guide rod  46 , which increases the efficiency of the gas spring assembly  26 . 
     As noted above, and with reference to  FIGS. 1 through 3 , the trigger assembly  24  includes a housing  38  supporting a sear  42 . Preferably, and as shown, the sear  42  includes a planar portion  78 , which presents a catch  80  for engaging a ledge  82  on the latch bushing  50  in latching engagement. The planar portion  78 , including the catch  80 , generally moves in a vertical direction, along a plane of the planar portion  78 , as the trigger assembly  24  is moved from the de-cocked position into the cocked position. 
     Referring to  FIG. 3 , the first end  64  of the guide rod  46  includes a first arm portion  84  and a second arm portion  86 , each extending along the longitudinal axis  54  to a respective distal end, and cooperating to define a slot  88  therebetween. The first end  64  of the guide rod  46  is disposed in abutting engagement with the housing  38  of the trigger assembly  24 . More specifically, the distal ends of the first arm portion  84  and the second arm portion  86  engage the housing  38  of the trigger assembly  24  in abutting engagement. When the sear  42  is disposed in the cocked position, the planar portion  78  of the sear  42 , including the catch  80 , is at least partially disposed within the slot  88 , between the first arm portion  84  and the second arm portion  86 . Accordingly, the slot  88  provides the space or clearance necessary for the planar portion  78  of the sear  42 , including the catch  80  to move into the cocked position. If not for the presence of the slot  88 , the planar portion  78  of the sear  42  would be blocked from moving into the cocked position by the first end  64  of the guide rod  46 . 
     Referring to  FIGS. 4 and 5 , the latch bushing  50  includes a contact end  90  that is axially spaced, along the longitudinal axis  54 , from the rearward end  58  of the annular wall  48  of the piston  44 . Referring to  FIG. 2 , the contact end  90  of the latch bushing  50  contacts the sear  42  at an axial location along the longitudinal axis  54  that is disposed rearward of the catch  80  of the sear  42 . The latch bushing  50  defines the ledge  82  for engaging the catch  80  of the sear  42  in latching engagement. Preferably, and as shown in  FIGS. 4 and 5 , the latch bushing  50  defines a window  92  extending through an outer wall  94  of the latch bushing  50 , into the central bore  62  of the latch bushing  50 . The window  92  includes an edge  96 , which is defined by a thickness  98  of the outer wall  94 . The edge  96  of the window  92  defines the ledge  82  for engaging the catch  80  of the sear  42  in latching engagement. Preferably, the ledge  82  is disposed nearer the longitudinal axis  54  than the annular wall  48  of the piston  44 , so as to form an in-line latching system. 
     As shown in  FIG. 1 , the contact end  90  of the latch bushing  50  is de-coupled from the sear  42  of the trigger assembly  24  when the trigger assembly  24  is in the de-cocked position and the piston  44  is in the un-compressed position. As shown in  FIG. 2 , the contact end  90  of the latch bushing  50  is releasably coupled to the sear  42  of the trigger assembly  24  when the trigger assembly  24  is in the cocked position, and the piston  44  is in the compressed position. Axial movement of the piston  44  along the longitudinal axis  54 , from the un-compressed position into the compressed position, brings the contact end  90  of the latch bushing  50  into pressing engagement with the sear  42 , and moves the sear  42  from the de-cocked position into the cocked position. As the sear  42  moves from the de-cocked position into the cocked position, the catch  80  of the sear  42  engages the ledge  82  in latched engagement to secure the piston  44  within the compression chamber  32  relative to the trigger housing  22 . 
     Referring to  FIGS. 1 and 2 , movement of the piston  44  from the un-compressed position, shown in  FIG. 1 , into the compressed position, shown in  FIG. 2 , brings the contact end  90  of the latch bushing  50  into latching engagement with the sear  42  of the trigger assembly  24 . Actuation of the trigger assembly  24  from the cocked position to the de-cocked position de-couples the latch bushing  50  from the sear  42  of the trigger assembly  24 . De-coupling the sear  42  of the trigger assembly  24  from the latch bushing  50  permits the compressed air within the interior pressure chamber  56  to decompress or expand the gas spring assembly  26 , which moves the piston  44  along the longitudinal axis  54 , thereby compressing the air within the compression chamber  32 , which in turn propels the projectile  30  out of the barrel  28 . 
     Referring to  FIGS. 1 and 2 , the gas spring assembly  26  includes a static seal  100 , which is disposed between the piston  44  and latch bushing  50 . The static seal  100  is operable to seal the interior pressure chamber  56 , between the piston  44  and the latch bushing  50 . The static seal  100  is coupled to an exterior surface of the latch bushing  50 , and engages an interior surface of the piston  44 . The static seal  100  may include any device capable of sealing between the piston  44  and latch bushing  50 , such as but not limited to a rubber O-ring/gasket or similar device. Furthermore, the static seal  100  may include multiple devices positioned axially adjacent each other along the longitudinal axis  54 . 
     The gas spring assembly  26  further includes a dynamic seal  102 . The dynamic seal  102  is disposed between an interior surface of the central bore  62  of the latch bushing  50  and the guide rod  46 . The dynamic seal  102  is operable to seal the interior pressure chamber  56  between the latch bushing  50  and the guide rod  46 . The dynamic seal  102  must seal between the latch bushing  50  and the guide rod  46 , while stationary and while the latch bushing  50  is moving relative to the guide rod  46 . The dynamic seal  102  may include, but is not limited to, a rubber  0 -ring or other similar device. 
     As noted above, the latch bushing  50  includes a bushing length  76  that is measured along the longitudinal axis  54 . The bushing length  76  of the latch bushing  50  may be used to control the displacement of the guide rod  46  within the interior pressure chamber  56  of the gas spring assembly  26 . As such, a spring force generated by the gas spring assembly  26 , when disposed in the compressed position, may be dependent upon the bushing length  76  of the latch bushing  50 . While the latch bushing  50  is shown as a single manufacture, including both the dynamic seal  102  and the static seal  100 , it should be appreciated that the latch bushing  50  may be manufactured from two separate components, a first component that is fixedly attached to the annular wall  48  of the piston  44  and includes the static seal  100 , and a second component that includes a tubular portion that defines the central bore  62  and includes the dynamic seal  102 . In so doing, the spring force of the gas spring assembly  26  may be easily changed by replacing the second component with a tubular portion of a different bushing length  76 . Furthermore, it should be appreciated that the latch bushing  50  may be configured differently than shown and described herein. 
     As shown in  FIGS. 1-2, 4-5, and 8 , the air gun  20  may also include a damping/support bushing  103 . The damping/support bushing  103  is disposed annularly about the tubular portion of the latch bushing  50 , adjacent the rearward end  58  of the annular wall  48  of the piston  44 . The damping/support bushing  50  is disposed in radial contact with an inner surface of the compression tube  25 , about the longitudinal axis  54 . The damping/support bushing  103  is manufactured from a material capable of both damping vibration in the gas spring assembly  26 , as well as radially support the latch bushing  50  and the guide rod  46  relative to the longitudinal axis  54 . The material of the damping/support bushing  103  should also include a low coefficient of friction to minimize frictional forces between the damping/support bushing  103  and the compression tube  25 . The damping/support bushing supports the latch bushing  50  to promote smooth, in-line movement during engagement of the latch bushing  50  with the trigger assembly  24 , and during the firing cycle. Consistent, in-line movement of the latch bushing  50  and the guide rod  46  provides a linear firing cycle along the longitudinal axis  54 , which increases output performance of the air gun  20 , and reduces shot velocity variations. Additionally, the damping/support bushing  103  dampens harmonic noise created by the gas spring assembly  26  when the piston  44  slams forward during the firing cycle. 
     Referring to  FIGS. 6 and 7 , the piston  44  includes a charging valve system  104 . When a fluid pressure in the compression chamber  32  is greater than a fluid pressure in the interior pressure chamber  56  of the gas spring assembly  26 , the charging valve system  104  is automatically operated to open fluid communication between the interior pressure chamber  56  and the compression chamber  32 . The charging valve system  104  opens fluid communication to allow fluid, e.g., air or nitrogen, to flow into of the interior pressure chamber  56  of the gas spring assembly  26 , thereby increasing the fluid pressure within the interior pressure chamber  56 . When the fluid pressure in the compression chamber  32  is equal to or less than the fluid pressure in the interior pressure chamber  56 , the charging valve system  104  automatically operates to close fluid communication between the interior pressure chamber  56  of the gas spring assembly  26  and the compression chamber  32 , to prevent fluid from escaping the interior pressure chamber  56  of the gas spring assembly  26  and maintain the fluid pressure within the interior pressure chamber  56 . The charging valve system  104  may be manually operated to open fluid communication between the interior pressure chamber  56  of the gas spring assembly  26  and the compression chamber  32 , to allow fluid to escape from within the interior pressure chamber  56  to decrease the fluid pressure within the interior pressure chamber  56 . 
     As shown in the Figures, the charging valve system  104  is disposed in the end wall  52  of the piston  44 . The charging valve system  104  includes a piston port  106 , which extends through the end wall  52  of the piston  44 , into an interior pocket  108  defined by the end wall  52  and disposed within the interior pressure chamber  56 . A ball  110  is disposed within the interior pocket  108  of the end wall  52 . The ball  110  is seated adjacent an interior rim  112  of the piston port  106 . The ball  110  is operable to block fluid communication through the piston port  106 . 
     A retaining mechanism  114  is positioned within the interior pressure chamber  56  and operable to secure the ball  110  within the interior pocket  108 . The retaining mechanism  114  may include, for example, an annular plate  116  having a circumference sized to snuggly fit within an undercut  118  formed into the interior surface of the end wall  52 . The annular plate  116  may be manufactured from a plastic, so that it may be temporarily and elastically deformed during insertion into the undercut  118 . The annular plate  116  includes at least one aperture  120  extending therethrough to allow fluid communication through the annular plate  116 , between the interior pressure chamber  56  and the pocket of the end wall  52 . The annular plate  116  is positioned adjacent the ball  110  a distance sufficient to allow the ball  110  to move axially along the longitudinal axis  54  to open fluid communication to the piston port  106 , while preventing the ball  110  from becoming dislodged from the pocket of the end wall  52 . 
     The charging valve system  104  may include a port seal  122 . The port seal  122  is disposed between the end wall  52  and the ball  110 , around the interior rim  112  of the piston port  106 . The port seal  122  is operable to seal between the ball  110  and the end wall  52 . The port seal  122  guides the ball  110  into seated engagement with the piston port  106  to block the piston port  106 . The port seal  122  may include any suitable seal, such as but not limited to a rubber o-ring or other similar device. The port seal  122  includes an outer circumference that is substantially equal to a circumference of the interior pocket  108  in the end wall  52 , such that the port seal  122  remains secured in place by friction contact with the interior pocket  108 . 
     When the fluid pressure within the compression chamber  32  is greater than the fluid pressure within the interior pressure chamber  56  of the piston  44 , thereby creating a pressure differential, the ball  110  is automatically unseated from the interior rim  112  of the piston port  106  and moved axially along the longitudinal axis  54  away from the piston port  106 . Unseating the ball  110  allows or opens fluid communication between the compression chamber  32  and the interior pressure chamber  56 . When the fluid pressure within the interior pressure chamber  56  of the piston  44  is equal to or greater than the fluid pressure within the compression chamber  32 , the pressure differential therebetween automatically seats the ball  110  against the port seal  122  and the interior rim  112  of the piston port  106 , to seal the interior pressure chamber  56  and prevent fluid communication between the interior pressure chamber  56  and the compression chamber  32 . When the fluid pressure within the interior pressure chamber  56  of the piston  44  is equal to or greater than the fluid pressure within the compression chamber  32 , the ball  110  may be manually moved away from the piston port  106  and the port seal  122  to open fluid communication through the piston port  106  and allow fluid to escape from the interior pressure chamber  56 . The ball  110  may be manually moved, for example, by inserting a small diameter tool, such as a pin or wire, through the piston port  106  and pressing the ball  110  away from the piston port  106  and against the annular plate  116  of the retaining mechanism  114 . 
     Referring to  FIG. 6 , the compression tube  25  may define a pressure port  124  disposed in fluid communication with the compression chamber  32 . As shown, the pressure port  124  is disposed in fluid communication with a firing port  126 . The firing port  126  connects the compression chamber  32  and a bore  128  of the barrel  28  in fluid communication. The pressure port  124  is in fluid communication with the compression chamber  32  through the firing port  126 . The pressure port  124  is operable to introduce a pressurized gas into the compression chamber  32 . 
     A pressurized gas valve fitting  130  may be disposed in the pressure port  124 . The pressurized gas valve fitting  130  is operable or moveable between a sealed position and a release position. When disposed in the sealed position, the pressurized gas valve fitting  130  seals the pressure port  124 . When disposed in the release position, the pressurized gas valve fitting  130  allows fluid communication through the pressure port  124 . The pressurized gas valve fitting  130  may include, but is not limited to, a Schrader valve, a Presta valve, or some other valve device. 
     In order to allow the introduction of pressurized gas into the compression chamber  32 , and prevent the pressurized gas from escaping the pressure chamber  32 , the pressurized gas valve fitting  130  may include a ball  132  seated against a rim  133  of the pressure port  124 . A seal  134 , such as an o-ring or other similar device seals between the wall of the pressure port  124  and a shank portion  136  of the pressurized gas valve fitting  130 . The seal  134  is disposed between the ball  132  and the shank portion  136  of the pressurized gas valve fitting  130 . Pressurized gas that is introduced into the compression chamber  32  via the pressurized gas valve fitting urges the ball  132  away from the seal  134 , i.e., into the release position, thereby allowing the pressurized gas to flow around the ball and through the rim  133  of the of the pressure port  124 . Pressurized gas from within the compression chamber  32  urges the ball  132  into sealing engagement with the seal  134 , i.e., the sealed position, thereby preventing the escape of the pressurized gas from the compression chamber  32 . 
     When the pressurized gas valve fitting  130  is disposed in the release position, pressurized gas, from a pressure source such as but not limited to a compressed gas cylinder or a pump, may be introduced into the compression chamber  32  through the pressurized gas valve fitting  130 . Introducing the pressurized gas into the compression chamber  32  increases the fluid pressure within the compression chamber  32 . If the fluid pressure within the compression chamber  32  is increased to a level greater than the fluid pressure within the interior pressure chamber  56  of the gas spring assembly  26 , the charging valve system  104  will automatically open and allow the pressurized gas within the compression chamber  32  to flow into the interior pressure chamber  56 , thereby increasing the fluid pressure within the interior pressure chamber  56  of the gas spring assembly  26 , while the gas spring assembly  26  is disposed within the compression chamber  32  of the trigger housing  22 . When the pressurized gas source is removed and the pressure within the compression chamber  32  falls below that fluid pressure within the interior pressure chamber  56  of the gas spring assembly  26 , the charging valve system  104  closes, thereby retaining the gas within the interior pressure chamber  56  and maintaining the fluid pressure of the gas spring assembly  26 . It should be appreciated that in the exemplary embodiment shown, the firing port  126  must be blocked and/or plugged in order to introduce the pressurized gas into the compression chamber  32  via the pressure port  124 . 
     Referring to  FIG. 8 , an alternative embodiment of the air gun is generally shown at  200 . Throughout  FIG. 8 , features and components that are common to the embodiment of the air gun  20  shown in  FIGS. 1 through 7  are identified with the same reference numerals used in  FIGS. 1 through 7 . As shown in  FIG. 8 , the gas spring assembly  26  is disposed within an interior chamber  202  of an outer piston  204 . The air gun  200  generally operates in the same manner as the air gun  20  described above. The difference between the first embodiment of the air gun  20  and the alternative embodiment of the air gun  200  is that the lever  36  is coupled to the outer piston  204 , such that movement of the barrel  28  between the firing position and the cocking position directly moves the outer piston  204 . Movement of the outer piston  204  thereby moves the piston  44  of the gas spring assembly  26  from the un-compressed position into the compressed position, the compressed position being shown in  FIG. 8 , thereby compressing the gas within the gas spring assembly  26 . As is described above in relation to the first embodiment of the air gun  20 , movement of the gas spring assembly  26  into the compressed position also moves the trigger assembly  24  from the de-cocked position into the cocked position, and latches the trigger assembly  24  to the gas spring assembly  26 . 
     The alternative embodiment of the air gun  200  may be manufactured by converting an existing coil spring assembly, to use a mass produced gas spring assembly  26 , such that the piston  44  of the gas spring assembly  26  does not need to be exactly sized to the specific internal dimensions of the compression tube  25 . Rather, the gas spring assembly  26  is merely positioned inside the already existing piston, i.e., the piston  204  of the previous coil spring assembly. As such, it should be appreciated that the outer piston  204  may have been the piston of a pre-existing coil spring assembly. Upon firing the rifle, the piston  44  of the gas spring assembly  26  moves along the longitudinal axis, and pushes the outer piston  204  forward, thereby compressing the gas within the compression chamber  32 , and firing the projectile  30  as described above. 
     Referring to  FIG. 9 , an alternative embodiment of the air gun is generally shown at  300 . Throughout  FIG. 9 , features and components that are common to the embodiment of the air gun  20  shown in  FIGS. 1 through 7  are identified with the same reference numerals used in  FIGS. 1 through 7 . The embodiment of the air gun  300  shown in  FIG. 9  differs from the air gun  20  shown in  FIGS. 1 through 7  in the construction of the gas spring assembly  326 . Briefly, the gas spring assembly  326  includes a shank portion  368  of a guide rod  346  separate from a head portion  370 , and includes an inner support tube  438  disposed within the interior pressure chamber  56  of the piston  44  for supporting the head portion  370 . 
     Referring to  FIG. 9 , the gas spring assembly  326  includes the piston  44 , including the annular wall  48  and the end wall  52  that at least partially define the interior pressure chamber  56 , and the latch bushing  50  attached to the annular wall  48  adjacent the rearward end of the annular wall  48  to further define the interior pressure chamber  56 , as set forth and described above with reference to  FIGS. 1 through 7 . 
     The inner support tube  438  is disposed within the interior pressure chamber  56  of the piston  44 . The inner support tube  438  is axially and radially supported by the latch bushing  50  and the end wall  52  respectively, to limit axial and radial movement of the inner support tube  438  relative to the longitudinal axis  54  and/or the piston  44 . The inner support tube  438  may be radially supported by the latch bushing  50  and/or the end wall  52  via an undercut or other similar annular support structure within which the inner support tube  438  is supported. The inner support tube  438  defines an inner bore  440  that extends along the longitudinal axis  54 , between the latch bushing  50  and the end wall  52 . The inner bore  440  of the inner support tube  438  is concentric with the central bore  62  of the latch bushing  50 . A forward end  442  of the inner support tube  438  is disposed against the end wall  52  of the piston  44 . However, even though the forward end  442  of the inner support tube  438  abuts the end wall  52  of the piston  44 , the abutting engagement does not form a seal, and therefore, the forward end  44  is not sealed against the end wall  52  of the piston  44 . Because the forward end  44  is not sealed against the end wall  52  of the piston  44 , pressurized gas may flow between a portion  444  of the interior pressure chamber  56  defined by the inner bore  440  of the inner support tube  438 , and a portion  446  of the interior pressure chamber  56  defined between the inner support tube  438  and an interior surface of the annular wall  48 . 
     The inner support tube  438  may optionally include a bleed port  448  that extends radially through the inner support tube  438 , so that gas may flow between the portion  444  of the interior pressure chamber  56  defined by the inner bore  440  of the inner support tube  438 , and the portion  446  of the interior pressure chamber  56  defined between the inner support tube  438  and the interior surface of the annular wall  48 . 
     The head portion  370  is disposed within the inner bore  440  of the inner support tube  438 . The head portion  370  is moveable within the inner bore  440  relative to the inner support tube  438  and the piston  44 . The head portion  370  is axially moveable along the longitudinal axis  54 . The gas spring assembly  326  may include a dynamic head seal  450  that is disposed between the head portion  370  and the inner support tube  438 . The dynamic head seal  450  is operable to seal between an interior radial surface of the inner support tube  438  and an exterior radial surface of the head portion  370 . 
     The guide rod  346  is slideably supported within the central bore  62  of the latch bushing  50 . The guide rod  346 , the latch bushing  50 , the piston  44 , the head portion  370 , and the inner support tube  438  are all co-axially disposed relative to each other along the longitudinal axis  54 . As described above related to the embodiment of the air gun  20  shown in  FIGS. 1 through 7 , the piston  44  is axially moveable along the longitudinal axis  54  relative to the guide rod  346  between the compressed position and the un-compressed position. 
     Similar to the guide rod  46  shown in  FIGS. 1 through 7 , the guide rod  346  includes the first end  64  (not shown in  FIG. 9 ) for engaging the trigger assembly  24  in abutting engagement. Additionally, the guide rod  346  includes a second end  366 . However, whereas the guide rod  46  shown in the embodiment of the air gun  20  shown in  FIGS. 1 through 7  included the head portion  70 , the second end  366  of the guide rod  346  shown in  FIG. 9  does not include the head portion  70  integrally formed therewith. Rather, the second end  366  of the guide rod  346  shown in  FIG. 9  engages the separate and independent head portion  370  within the inner bore  440  of the inner support tube  438 . Accordingly, the guide rod  346  and the head portion  370  are separate and distinct components of the air spring assembly, and are not attached together, which is the primary difference between the embodiment of the air gun  20  shown in  FIGS. 1 through 7 , and the embodiment of the air gun  300  shown in  FIG. 9 . The head portion  370  may define a recess  454 , and the guide rod  346  may include a projection  456  sized to fit within the recess  454 . The projection  456  is seated within the recess  454 . 
     The guide rod  346  includes a shank portion  368  defining a first diameter  72 . The shank portion  368  is disposed adjacent the second end  366  of the guide rod  346 . The first diameter  72  is substantially equal to the diameter of the central bore  62  of the latch bushing  50 , so that the guide rod  346  may be inserted and/or withdrawn through the central bore  62  of the latch bushing  50 . The head portion  370  defines the second diameter  74 . The second diameter  74  of the head portion  370  is larger than the first diameter  72  of the shank portion  368 , and is larger than the diameter of the central bore  62 , such that the head portion  370  may not pass through the central bore  62 . 
     The second end  366  of the guide rod  346  engages the head portion  370  to bias against the head portion  370  as the piston  44  is moved from the un-compressed position into the compressed position. With the guide rod  346  biasing against the head portion  370  as the piston  44  is moved, the piston  44  and the inner support tube  438  move relative to the head portion  370  axially along the longitudinal axis  54 , such that the head portion  370  moves within the inner bore  440  of the inner support tube  438 . As described above relative to the embodiment of the air gun  20  shown in  FIGS. 1 through 7 , as the head portion  370  is moved further into the interior pressure chamber  56 , the gas within the interior pressure chamber  56  is compressed by the displacement caused by the guide rod  346  within the interior pressure chamber  56 . As the head portion  370  is moved relative to the inner support tube  438 , and the gas within the inner bore  440  of the inner support tube  438  is compressed, the gas bleeds or flows around the forward end  442  of the inner support tube  438 , between the forward end  442  of the inner support tube  438  and the end wall  52 , and/or flows through the bleed port  448 , into the portion  446  of the interior pressure chamber  56  disposed between the annular wall  48  and the inner support tube  438 . 
     The force generated by the gas spring assembly  326  is dependent upon the volume of the pressurized gas contained within the interior pressure chamber  56  of the piston  44 . Accordingly, by changing an axial length of the head portion  370 , or a wall thickness of the inner support tube  438 , for example, the volume of gas within the interior pressure chamber  56  may be reduced or increased, thereby decreasing or increasing the force generated by the gas spring assembly  326  respectively. 
     The speed of the piston  44  during firing may also be controlled, by changing the cross sectional area of the bleed port  448 , or a space between the forward end  442  of the inner support tube  438  and the end wall  52 . When the air gun  20  is fired, the piston  44  moves forward, away from the forward end  442  of the inner support tube  438 . In order to allow the piston  44  to move forward, gas, e.g., air, must be able to flow into the portion  444  of the interior pressure chamber  56  defined by the inner bore  440  of the inner support tube  438 , in order to prevent the formation of a vacuum that would prevent the piston  44  from moving. The size or area of the bleed portion  448 , and/or the distance or space between the forward end  442  of the inner support tube  438  and the end wall  52  controls how fast the gas may flow into the portion  444  of the interior pressure chamber  56 . An increase in the area increases the rate at which the gas may flow into the portion  444  of the interior pressure chamber  56 , which allows the piston  44  to move faster. A decrease in the flow area decreases the rate at which the gas may flow into the portion  444  of the interior pressure chamber  56 , which slows the speed of the piston  44 . The speed of the piston  44  affects the speed of the projectile  30  when fired. For a given caliber and weight of the projectile  30 , an increase in the speed of the piston  44  when fired increases the fired velocity of the projectile  30 . In contrast, for a given caliber and weight of the projectile, a decrease in the speed of the piston  44  when fired decreases the fired velocity of the projectile  30 . Accordingly, the gas spring assembly  326  provides yet another advantageous method of tailoring or tuning the operation of the air gun  20  to achieve optimum performance. 
     Additionally, because the guide rod  346  is not attached to the head portion  370 , the guide rod  346  may be shipped separately from the pressurized piston  44 , and then simply inserted through the central bore  62  of the latch bushing  50 , and into abutting engagement with the head portion  370  to assemble the gas spring assembly  326 , prior to installation into the air gun  300 . 
     The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed teachings have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims.