Abstract:
A man-powered system for pneumatically launching a pellet cluster includes a cartridge for holding the pellet cluster. A hollow propulsion shaft receives the cartridge for substantially free travel back and forth in the shaft to establish a variable-volume compression chamber in the shaft, between the cartridge and a closed end of the shaft. When a driving force acts to launch the combination of cartridge and shaft, the cartridge moves to compress gas in the compression chamber for a subsequent expansion that will propel the cartridge forward through the shaft. After launch, the compressed gas acts to separate the pellet cluster from the cartridge and to provide a pneumatic assist that increases the velocity of pellets after separation.

Description:
[0001]    This application is a continuation-in-part of application Ser. No. 13/789,514, filed Mar. 7, 2013, which is currently pending. The contents of application Ser. No. 13/789,514 are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains generally to man-powered devices for launching pellet clusters. More particularly, the present invention pertains to man-powered launchers that provide a pneumatic assist to pellets as they are being launched. The present invention is particularly, but not exclusively, useful as a man-powered device that provides, in combination, a cartridge for holding a pellet cluster and a propulsion tube for interacting with the cartridge to create compressed gas during a launch, to thereby provide a pneumatic assist for increasing the velocity for the pellets after they become separated from the cartridge. 
       BACKGROUND OF THE INVENTION 
       [0003]    An important factor for evaluating the performance of a man-powered launcher is the velocity at which a projectile is released from the launcher. Regardless whether the projectile is an arrow, a bolt, or a shot cluster, and regardless whether the projectile is launched by either a vertical bow or a crossbow, the resultant projectile velocity is an important measure of the launcher&#39;s performance. In the event, the resultant projectile velocity will be a function of the amount of energy (i.e. the capacity to perform work) that can be stored in the launcher prior to projectile launch, and thereafter used to propel the projectile onto its flight path. For the specific case of a man-powered weapon, a contributing factor for performance is the physical ability of the user. 
         [0004]    In general, energy can be classified as being either thermal energy, potential energy or kinetic energy. Of primary interest here are potential and kinetic energy. By definition, potential energy is the energy which is possessed by a body by virtue of its position or condition relative to other bodies. For example, an object weighing one pound, when positioned ten feet above a surface prior to being dropped onto the surface, will expend ten foot-pounds of energy when it impacts against the surface. In this example, by virtue of its position relative to the surface, the one pound object had a potential energy of ten foot-pounds. As another example of potential energy, a compressed gas has a potential energy for performing work as it is allowed to expand. On the other hand, unlike potential energy, kinetic energy is the energy (work capacity) that a body possesses by virtue of being in motion. Mathematically expressed, kinetic energy is a function of the velocity of the object. Specifically, a particle having a mass “m”, that is moving with a linear velocity “v”, has a kinetic energy that is mathematically expressed as “½ mv 2 ”. As is well known, potential energy and kinetic energy are interchangeable. 
         [0005]    In light of the above, it is an object of the present invention to provide a device and method for converting the potential energy of a launching device into the potential energy of a compressed gas inside the projectile during a launch of the projectile; and then transferring this potential energy to a payload for use as kinetic energy that will increase velocity of the payload after the initial launch. Another object of the present invention is to provide a device and method for launching a projectile to achieve an in-flight velocity that otherwise exceeds the capability of the launching device. Yet another object of the present invention is to provide a device and method for launching a pellet cluster from a man-powered launcher. Still another object of the present invention is to provide a device and method for launching projectiles with a pneumatically assisted operational velocity that is easy to use, is simple to implement and is comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with the present invention, a device and method are provided for launching a projectile from a man-powered device which will achieve an in-flight velocity that otherwise exceeds the capability of the launching device by itself. More specifically, in an energy transfer sequence, the potential energy that is initially established in the projectile launcher is converted into kinetic energy for the projectile as the projectile is launched onto its flight path. Next, the kinetic energy that is imparted to the projectile is then, at least in part, converted into potential energy by compressing gas in a chamber, inside the projectile. In turn, this potential energy is transferred to a payload, as the compressed gas is allowed to expand, for use as kinetic energy that will increase payload velocity after the initial launch. Note that this multistep energy conversion process occurs in a dynamic fashion, such that various steps of the process may overlap in time. 
         [0007]    Structurally, a device for the present invention includes a first component that is tubular shaped and is formed with a lumen which defines an axis. Further, the first component has an open end and a closed end. Also included in the device of the present invention is a second component that is engaged with the first component to create an assembly. Specifically, this assembly establishes a gas-filled compression chamber in the lumen of the first component that is located between the second component and the closed end of the first component. Within this combination, the assembly allows for a substantially free axial movement of the second component back and forth in the compression chamber of the assembly. Further, depending on the embodiment of the present invention, a payload is selectively mounted on a component of the assembly. For the present invention, the payload may be either a conventional arrow (e.g. a broadhead) as used with a vertical bow (launcher), a bolt as used with a crossbow (launcher), or a shot cluster that may be adapted for use by either type launcher. 
         [0008]    As envisioned for the present invention, a man-powered launcher will be used to generate an axially-directed driving force on one component of the assembly (projectile) in order to propel the projectile from the launcher and onto its flight path. A consequence of this driving force is to cause a relative movement between the first component and the second component. Recall, the second component is free to move within the lumen of the first component (i.e. it is free to move within the gas chamber of the assembly). In the event, this movement further compresses gas in the compression chamber to thereby increase potential energy in the compressed gas. 
         [0009]    Once gas in the compression chamber has been compressed as much as possible, which occurs at or about the time when the driving force becomes zero, the gas then begins to expand. During this expansion, potential energy in the gas is converted to kinetic energy by equal and opposite forces to both the first and second components. This causes a resultant increase in the velocity of one component, and a resultant dissipation in the velocity of the other component; a combination of events that separates the payload from the assembly. 
         [0010]    With the above in mind, the present invention envisions two different types of operational embodiments. In one, the payload is mounted on the second component, and the driving force is generated on the first component. In the other embodiment, the payload is mounted on the first component and the driving force is generated on the second component. In either embodiment, the mass of the proximal (i.e. aft) component (m p ) can be less than the mass of the distal (i.e. forward) component (m d ). For both embodiments, the driving force for launch is exerted against the proximal component. 
         [0011]    For an operation of the present invention, a launcher is selected and is configured (i.e. armed) for launch. Stated differently, the launcher is configured to store potential energy. A projectile is then positioned on the launcher for launch. Upon firing the launcher, the potential energy that is stored in the launcher is converted to kinetic energy by way of the driving force that acts to propel the projectile from the launcher. Specifically, this driving force acts on the projectile and is directed to accelerate the projectile along an axial path that is defined by the projectile. 
         [0012]    During the initial acceleration of the projectile by the driving force, a first kinetic energy is generated for the first component of the assembly, and a second kinetic energy is generated for the second component of the assembly. All of this happens for separate but interrelated reasons. Specifically, the different components of the assembly will preferably be of different mass, and they can have different velocities at launch (recall: kinetic energy equals ½ mv 2 ). In more detail, the different velocities occur because, while the driving force acts directly on the first component to accelerate it along the flight path, the second component experiences no such direct force. Instead, the second component tends to remain at rest and is accelerated only by forces exerted on it by the gas which is compressed in the compression chamber. 
         [0013]    Simultaneously, as kinetic energy is imparted to the first and second components of the assembly, a potential energy is stored within the gas in the gas-filled chamber of the assembly. Specifically, this increase in potential energy occurs because the second component moves toward the first component during the initial acceleration, and the gas is compressed between components as the gas chamber is diminished in size. At the end of the first component&#39;s initial acceleration, the gas has been compressed as much as possible and it has its highest potential energy. 
         [0014]    After the initial acceleration of the projectile (i.e. when the driving force becomes zero), the potential energy of the gas is converted into kinetic energy and an expansion of the gas acts on both the first component and the second component. The result here is an additional acceleration of the second component and its payload for separation of the payload from the projectile (assembly), and by a deceleration of the remainder of the projectile. 
         [0015]    In an adaptation of the present invention, a projectile assembly is provided for pneumatically launching a pellet cluster from a man-powered launcher. In combination, as indicated above, the projectile assembly includes a cartridge for holding the pellet cluster and a hollow propulsion shaft for receiving the cartridge in its lumen. In this combination, the cartridge and the propulsion shaft interact with each other to generate additional pneumatic potential energy that will launch the pellet cluster at an increased velocity from the cartridge. Pellets in the pellet cluster are preferably made of a material such as tungsten or steel. 
         [0016]    In detail, the elongated tubular-shaped cartridge (sabot) of the projectile assembly has an open distal end and a closed proximal end. Further, the cartridge includes a retention groove which is formed at its proximal end, and it has an O-ring assembly that is positioned in the retention groove to establish a substantially airtight seal between the proximal end of the cartridge and an inner sidewall of the propulsion shaft. 
         [0017]    Structurally, the O-ring assembly includes an outer ring that is positioned in the retention groove for direct contact with an inner surface of the propulsion shaft. Preferably, the outer ring is made of polytetrafluoroethylene (PTFE), and it is formed with a diagonal split that allows for expansion and contraction of the outer ring. The O-ring assembly also has an inner ring that is made of rubber and is positioned in the retention groove to produce a force against the outer ring that urges the outer ring into contact against the inner surface of the propulsion shaft. Further, the retention groove is formed with at least one vent hole to equalize pressure between the retention groove and the compression chamber during a launch of the pellet cluster. 
         [0018]    Also included with the cartridge of the present invention is a retainer that is positioned in the lumen of the cartridge at its distal end. Specifically, the purpose of the retainer is to maintain the pellet cluster in the lumen of the cartridge prior to launch. Preferably, the retainer is a plurality of light weight tubes. 
         [0019]    Additionally, the cartridge includes a friction collar that is positioned in a snug engagement against the outer surface of the cartridge. The purpose of this friction collar is to generate friction forces against the cartridge that will retard movement of the cartridge during the separation of the pellet cluster from the cartridge. In particular, the friction collar is preferably made of aluminum and it will exert a radial pressure against the cartridge of approximately 500 psi. Further, a slide ring assembly is positioned on the outer surface of the cartridge, distal to the friction collar. The purpose here is to mitigate impact forces against the friction collar at the launch of the pellet cluster. 
         [0020]    For its structural cooperation with the cartridge of the present invention, the elongated, cylindrical-shaped propulsion shaft is dimensioned to receive the cartridge for substantially free travel back and forth in the lumen of the shaft. As previously disclosed, the propulsion shaft has a closed proximal end. Thus, the propulsion shaft interacts with the cartridge to establish a compression chamber in the lumen of the shaft between the closed proximal end of the cartridge and the closed proximal end of the propulsion shaft. As also previously disclosed, the volume of this compression chamber will change in response to movements of the cartridge back and forth in the shaft. 
         [0021]    The propulsion shaft further includes a pressure valve that is positioned at the proximal end of the propulsion shaft. As envisioned for the present invention, the pressure valve will be mounted in a nock, and the nock will be affixed to the proximal end of the propulsion shaft for operational interaction with the launcher of the projectile assembly. Specifically, the purpose of the pressure valve is to allow the compression chamber to be pressurized to a predetermined gauge pressure (e.g. 80 psig) prior to imparting the driving force against the shaft, to thereby provide an initial level of resistance to the compression of gas in the compression chamber. 
         [0022]    As an added feature for the projectile assembly, a ferrule is attached to the distal end of the propulsion shaft. In particular, the ferrule has a threaded extension projecting in a distal direction from the distal end of the shaft. A plug can then be joined in a threaded engagement with the ferrule to create an abutment around the open distal end of the propulsion shaft. This abutment then establishes a distal limit for movement of the cartridge in the lumen of the shaft. Also, because the plug is in a threaded engagement with the propulsion shaft, it can be easily removed for the replacement of a spent cartridge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which 
           [0024]      FIG. 1A  is an elevation view of a projectile in accordance with the present invention, shown mounted on a vertical cross bow for launch; 
           [0025]      FIG. 1B  is a view of the projectile as shown in  FIG. 1A  with the projectile at the release point where it is launched from the launcher; 
           [0026]      FIG. 1C  is a view of the projectile as shown in  FIGS. 1A and 1B  with the payload in flight toward a target after the payload has separated from the remainder of the projectile; 
           [0027]      FIG. 2  is a side view of a first preferred embodiment of a projectile in accordance with the present invention; 
           [0028]      FIG. 3  is a side view of an alternate second preferred embodiment of a projectile in accordance with the present invention; 
           [0029]      FIG. 4A  is a cross section view of a first preferred embodiment of the projectile of the present invention as seen along the line  4 - 4  in  FIG. 2 , prior to a launch of the projectile; 
           [0030]      FIG. 4B  is a cross section view of the first preferred embodiment of the projectile as seen in  FIG. 4A , at its release point, as it is being launched from the launcher; 
           [0031]      FIG. 4C  is a cross section view of the first preferred embodiment of the projectile as seen in  FIGS. 4A and 4B , after a payload has been separated from the remainder of the projectile; 
           [0032]      FIG. 5A  is a cross section view of a second preferred embodiment of the projectile of the present invention as seen along the line  5 - 5  in  FIG. 3 , prior to a launch of the projectile; 
           [0033]      FIG. 5B  is a cross section view of the second preferred embodiment of the projectile as seen in  FIG. 5A  at its release point, as it is being launched from the launcher; 
           [0034]      FIG. 5C  is a cross section view of the second preferred embodiment of the projectile as seen in  FIGS. 5A and 5B  after a payload has been separated from the remainder of the projectile; 
           [0035]      FIG. 6A  is a perspective view of a projectile assembly in accordance with the present invention with a cartridge (shown in phantom) positioned inside a propulsion shaft and ready for launch (see  FIG. 1A ); 
           [0036]      FIG. 6B  is a view of the projectile assembly shown in  FIG. 1A  with the cartridge positioned inside the propulsion shaft after the assembly has been accelerated by a driving force (see  FIG. 1B ); 
           [0037]      FIG. 7  is a side elevation view of a cartridge in accordance with the present invention; and 
           [0038]      FIG. 8  is a cross section view of the projectile assembly as seen along the line  8 - 8  in  FIG. 6A . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    Referring initially to  FIG. 1A , a device in accordance with the present invention is shown and is generally designated  10 . As shown, the device  10  includes a projectile  12  and a man-powered launcher  14 . In the particular case of the device  10  that is shown in  FIG. 1A , the launcher  14  is a vertical bow of a type well known in the art. The launcher  14 , however, could as well be a crossbow (not shown) or an air gun (not shown), both of which are of types well known in the pertinent art. 
         [0040]    As illustrated sequentially in  FIGS. 1A ,  1 B and  1 C, a purpose of the present invention is to use the launcher  14  to propel the projectile  12  along a flight path (dashed line)  16  toward a target  18 . In sequence,  FIG. 1A  shows the launcher  14  in a configuration for firing the projectile  12 .  FIG. 1B  then shows the projectile  12  as it is being released from the launcher  14 . And,  FIG. 1C  shows the projectile  12 , and its payload  20  after it has been separated from the projectile  12  in flight, after launch. In particular,  FIG. 1C  shows that shortly after launch, the payload  20  continues along the flight path  16  toward the target  18 , while the projectile  12 , itself, falls to the ground along a separation path (dotted line)  22 . 
         [0041]    From an energy perspective,  FIG. 1A  shows a projectile  12  that is ready to be shot from a launcher (vertical bow)  14 . In detail, the launcher  14  is configured to have a useable potential energy that can be converted into the kinetic energy of motion for the projectile  12 .  FIG. 1B  on the other hand, shows the projectile  12  at its release point from the launcher  14 , after the potential energy in the launcher ( FIG. 1A ) has been transferred to the projectile  12  as an internal mixture of potential energy and kinetic energy. In  FIG. 1C , the payload  20  is shown after its separation from the projectile  12 . 
         [0042]    In terms of energy transfer, the separation of payload  20  from projectile  12  is caused when a portion of the kinetic energy in the projectile  12  (at launch,  FIG. 1B ) is pneumatically converted into potential energy of compression inside the projectile  12 , and then reconverted into kinetic energy for the payload  20 . With this reconverted kinetic energy, the velocity “v” of the payload  20  is increased sufficiently to separate the payload  20  from the projectile  12 . Importantly, the payload  20  will substantially maintain the increased velocity “v”. 
         [0043]      FIGS. 2 and 3 , respectively, show two different embodiments for the present invention. In detail,  FIG. 2  (with cross reference to  FIGS. 4A-C ) shows a projectile  12  which includes a proximal component  24  that defines an axis  26 . For this embodiment of the present invention, a distal component  28  is positioned inside the proximal component  24  (see  FIG. 4A ). In another embodiment of the present invention, which is shown in  FIG. 3 , the distal component  28 ′ is positioned on the outside of the proximal component  24 ′. Both embodiments, respectively, include a nock  30  ( 30 ′) that is attached to the proximal component  24  ( 24 ′). Further, the embodiment for the device  12 ′ that is shown in  FIG. 3  also includes a plurality of fletches  32  that are attached to the distal component  28 ′, and a plurality of fletches  34  that are attached to the proximal component  24 ′. 
         [0044]    With reference to  FIG. 4A , it will be appreciated that the proximal component  24  is an elongated tube which is formed with a lumen  36  that extends along the length of the proximal component  24 . The lumen  36  has an open end  37 , and it has an arresting ring  38  which is located proximate the open end  37 . At the other end of the proximal component  24 , the nock  30  is affixed to the proximal component  24  to establish a closed end for the lumen  36 .  FIG. 4A  also shows that the distal component  28  of the projectile  12  is a cartridge  40  which holds a payload  20 . For the embodiment of the projectile  12  shown in  FIGS. 4A-C , the payload  20  is a shot cluster. Further, the cartridge  40  is shown to include a stabilizing ring  42  and a sealing ring  44  that together maintain an axial alignment for the cartridge  40  as it moves back and forth along the axis  26  inside the lumen  36  of the proximal component  24 . 
         [0045]    Still referring to  FIG. 4A , with the distal component  28  (i.e. cartridge  40 ) positioned inside the lumen  36  of the proximal component  24 , it will be appreciated that a compression chamber  46  is established between the cartridge  40  and the nock  30  of the projectile  12 . Importantly, the sealing ring  44  establishes a substantially air-tight seal for the compression chamber  46 . On the other hand, as evidenced by cross reference with  FIGS. 4B and 4C , the cartridge  40  must be allowed to freely move back and forth inside the lumen  36  of the proximal component  24 . Stated differently, it is essential to the operation of the present invention that the compression chamber  46  be dimensionally variable. 
         [0046]      FIGS. 5A-C  show another embodiment of the present invention wherein a compression chamber  48  is established in the lumen  36 ′ of the distal component  28 ′ of the projectile  12 ′. Specifically, for this embodiment, a sealing ring  50  is provided on the proximal component  24 ′ that interacts inside the lumen  36 ′ with the distal component  28 ′. With this interaction, a compression chamber  48  is established between the components  24 ′ and  28 ′. As with the compression chamber  46  for the embodiment of the projectile  12  (see  FIGS. 4A-C ), it is essential to the operation of the projectile  12 ′ of the present invention that the proximal component  24 ′ move freely relative to the distal component  28 ′, and that the compression chamber  48  thereby also be dimensionally variable. 
         [0047]    In an operation of the present invention, a driving force  52  (represented by the arrows  52  in  FIGS. 4A and 5A ) is applied to the projectile  12  ( 12 ′) by way of the nock  30  ( 30 ′). This occurs during a transformation of the launcher  14  between the consecutive configurations shown in  FIG. 1A  and  FIG. 1B . As shown in  FIGS. 4A-C , the effect of this driving force  52  on the projectile  12  is at least three-fold. For one (see  FIGS. 1A and 1B ), the projectile  12  will be accelerated to a launch velocity “v” for release from the launcher  14 . Simultaneously, in a second effect (see  FIGS. 4A and 4B ), the relatively unrestrained distal component  28  (i.e. cartridge  40 ) is caused to move forward more slowly (i.e. toward nock  30 ), against the resistance of gas in the compression chamber  46 . Thirdly, gas in the compression chamber  46  is compressed by the relative movement of the distal component  28  (cartridge  40 ) as the dimensions of the chamber  46  become smaller (see  FIG. 4B ). 
         [0048]    After the projectile  12  has been launched from the launcher  14  (see  FIG. 1B ), the driving force  52  no longer acts to accelerate the projectile  12 . Also, the potential energy that was generated by compressing gas in the compression chamber  46  reaches its maximum. As gas in the compression chamber  46  is then allowed to expand, its potential energy is converted into a kinetic energy that is manifested by an increased velocity for the cartridge  40 , and its payload  20 . This increased velocity then causes the payload  20  to separate from the cartridge  40  and to continue along the flight path  16  (see  FIG. 1C ). At the same time, as gas in the compression chamber  46  expands, the conversion of potential energy into kinetic energy is also manifested as a decrease in the velocity of the proximal component  24 . As intended for the present invention, this decrease in velocity of the proximal component  24  will result in the proximal component  24  being launched at a substantially lower velocity than the payload. A special case involves component  24  falling (generally vertically) to the ground along the separation path  22  (see  FIG. 1C ). 
         [0049]    A similar operational scenario occurs for the embodiment of projectile  12 ′ as shown in  FIGS. 5A-C . More specifically, as evidenced by a comparison of  FIG. 5A  with  FIG. 5B , the driving force  52  acts on the nock  30 ′ to accelerate the projectile  12 ′. This also compresses gas in the compression chamber  48  in the distal component  28 ′. In this case, however, the payload  20 ′ is mounted directly on the distal component  28 ′ and, thus, both the payload  20 ′ and distal component  28 ′ are separated from the proximal component  24 ′. In the event, expanding gas in the compression chamber  48  acts to increase the velocity of the distal component  28 ′ (payload  20 ′) and to diminish the velocity of the proximal component  24 ′. 
         [0050]    Referring now to  FIG. 6A , a projectile assembly in accordance with the present invention is shown and is generally designated  54 . In overview,  FIG. 6A  shows that the projectile assembly  54  includes a propulsion shaft  56  for receiving a cartridge  40  (shown in phantom) inside the shaft  56 . In their structural cooperation with each other, the cartridge  40  and the propulsion shaft  56  together create the compression chamber  46  as generally disclosed above.  FIGS. 6A and 6B  both show that the projectile assembly  54  also includes a plug  58 , and they indicate that the plug  58  is threaded into engagement with a ferrule  60  which is affixed to the distal end  62  of the propulsion shaft  56 . Note:  FIG. 6A  is comparable to  FIG. 1A , and  FIG. 6B  is comparable to  FIG. 1B . 
         [0051]      FIG. 7  shows that the external features of the cartridge  40  include a sabot  64  having a retention groove  66  that is affixed to its proximal end  68 . Importantly, the retention groove  66  closes the proximal end  68  of the sabot  64 . Further, it also includes a vent  70  that will establish fluid communication between the compression chamber  46  and the retention groove  66  when they are assembled with each other. It is also shown in  FIG. 7  that the cartridge  40  includes a friction ring  72  which is positioned on the sabot  64 . Preferably, the friction ring  72  is made of aluminum, and it is positioned on the sabot  64  to establish a “snug” fit that will typically create a radial pressure engagement between the sabot  64  and the friction ring  72  that is approximately five hundred psi. A slide ring assembly  74  is also provided for the cartridge  40 . In particular, the slide ring assembly  74  is located distal to the friction ring  72 , and it is provided to facilitate the interaction of the friction ring  72  with the propulsion shaft  56  during a launch of the payload  20  from the cartridge  40 . The internal features of the cartridge  40 , and the interaction of the cartridge  40  with the propulsion shaft  56  will be best appreciated with reference to  FIG. 8 . 
         [0052]      FIG. 8  indicates that the particular payload  20  of interest for this adaptation of the present invention is a cluster of pellets  76 . Preferably, the pellets  76  are made of either tungsten or steel, and they are dimensioned to be positioned and held inside the sabot  64 . In particular, a retainer  78  is used to hold the pellets  76  inside the sabot  64  until the pellets  76  are to be separated from the cartridge  40 , during a launch. In the embodiment shown in  FIG. 8 , the retainer  78  is a plurality of rings. 
         [0053]    It is also shown in  FIG. 8  that the cartridge  40  includes an O-ring assembly which includes both an outer ring  80  and an inner ring  82 . For purposes of the present invention, the outer ring  80  is preferably made of polytetrafluoroethylene (PTFE); more commonly known as Teflon®, a brand name of the DuPont Company. Further, the outer ring  80  is formed with a diagonal split (not shown) that allows for very slight variations in contraction and expansion of the outer ring  80  during an operation of the projectile assembly  54 . Also, as an integral part of the O-ring assembly, the inner ring  82  is preferably made of an elastomeric material (e.g. rubber) and it is positioned in the retention groove  66  with the outer ring  80 , substantially as shown. Specifically, in this combination, the inner ring  82  is positioned to urge against the outer ring  80 , to thereby force the outer ring  80  into direct contact with the inside of the propulsion shaft  56 . As envisioned for the present invention, this contact between the outer ring  80  and the propulsion shaft  56  will create a substantially airtight seal for the compression chamber  46  at the proximal end  68  of cartridge  40 . 
         [0054]    It is also important to note that the vent  70  in the retention groove  66  is provided to equalize gas pressure in the compression chamber  46  with gas pressure against the O-ring assembly (i.e. outer ring  80  and inner ring  82 ). Specifically, this is done to prevent the rapid build-up of pressure in the gas compression chamber  46  during a launch from having an adverse effect on the O-ring assembly. 
         [0055]    Still referring to  FIG. 8 , certain additional features of the present invention are also noteworthy. For one, at the distal end  62  of the propulsion shaft  56  it will be seen that the interaction of the plug  58  with the ferrule  60  creates an abutment  84 . The purpose here is to establish a structure for arresting the cartridge  40  during a separation of the pellets  76  from the cartridge  40 . Specifically, this happens when the sliding ring assembly  74  and friction ring  72  come into contact with the abutment  84  during a forward (distal) movement of the cartridge  40  through the propulsion shaft  56 . It is further noted that the plug  58  can be easily disengaged (i.e. unthreaded) from the ferrule  60  to remove and replace cartridges  40  in the propulsion shaft  56 . 
         [0056]    As another feature of the present invention, at the proximal end  86  of the propulsion shaft  56 , a pressure valve  88  (e.g. a Schrader valve) is provided. Preferably, the pressure valve  88  is mounted in the nock  30  as shown. The purpose here is to allow a pre-pressurization of the gas compression chamber  46  (e.g. 80 psig) prior to a launch of the projectile assembly  54 . This will provide an initial resistance to gas compression at launch that will maximize the performance characteristics of the projectile assembly  54 . 
         [0057]    While the particular Two-Phase Projectile with a Proximal Compression Chamber as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.