Patent Publication Number: US-2007107711-A1

Title: Low velocity projectile marker

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      There are no related applications on which priority is based. However, projectiles useful with the low velocity marker of the present invention are disclosed in the inventors&#39; co-pending application Ser. No. 11/126,889, filed May 11, 2005 and entitled “Reusable Marker Projectile”.  
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
      The inventions described and claimed in this application were not made under federally sponsored research and development.  
     BACKGROUND OF THE INVENTION  
      This invention relates to a projectile marker to pneumatically propel marker projectiles shot from a barrel. More specifically, this invention relates to a projectile marker with a low pressure propellant source to fire low velocity marker projectiles.  
      The sport of paintball is one of the fastest growing sports among teenagers and young adults. It is a combat type game in which players suitably attired in padded clothing and face shields shoot paint filled balls at each other through compressed air guns. On impact, the paintball typically breaks open to leave a splotch of water soluble, colored liquid. Suppliers of paintball equipment have substantially standardized the size of conventional paintballs to be approximately 0.688 to 0.690 inches or about 17.5 mm in diameter. The skin or capsule wall of a paintball is characteristically in the range of 0.2 to 0.4 mm in thickness so that the liquid volume contained within the paintball is a little more than 2.5 cubic centimeters. The weight of a typical paintball is slightly more than 3 grams. In short, it is a dense round ball and potentially dangerous.  
      The guns developed for shooting conventional paintballs include a barrel having a bore corresponding in size to the diameter of standard paintballs as previously mentioned. Such guns normally operate with compressed air or carbon dioxide (CO 2 ) gas stored in a removable, high pressure canister. The pressure canister, which may be a rechargeable type or it may be disposable, is a metal container capable of withstanding high gas pressures up to at least 4500 pounds per square inch (psi) or 316 kilograms per square centimeter (kg/cm 2 ). Typical operating pressures range from about 450 to 900 psi (32 to 63 kg/cm 2 ). The conventional paintball gun, therefore, is designed to propel a paintball weighing more than 3 grams at a velocity of approximately 300 feet per second or slightly more than 90 meters per second. The momentum of the paintball is sufficient on impact to cause bruising even under protective clothing. Although a strong desire to engage in this sport exists for pre-teenage youth, pain aversion among youngsters limits participation.  
      Due to the high pressures and velocities involved, it is well known that the sport of paintball and the associated use of paintball equipment pose very serious safety concerns. The industry is largely self regulated at the present. Responsible retailers limit sales of the guns to those over 18 years of age, and paintball venues, either outside or indoor arenas, characteristically limit paintball participation to those over 12 years of age and require signed parental consent to play. In addition to these initial safeguards, the combat games at public paintball facilities are carefully supervised with a variety of rules all designed to make the sport safer. Yet, injuries seem to be inevitable. Accordingly, the dangers associated with paintball have significantly limited participation by pre-teenage youth either through exercise of parental control or through age restrictions imposed by paintball field operators.  
      Another limiting factor associated with the sport of paintball is expense. During a staged combat on a paintball field, a player can shoot several hundred paintballs most of which break on contact with whatever they hit. Even those which remain unbroken cannot be reused due to distortion or dirt, either of which interfere with operation of the paintball gun if one attempts to reload a spent, but unbroken paintball.  
      Although it is impossible to eliminate all risks associated with any shooting recreation, nonetheless, a need exists in the sports industry to provide low pressure, low velocity projectile marker equipment for youth sports designed to reduce some of the risks of combat field sports and to lessen the impact experienced by a hit, while at the same time retaining the marking feature which has made the paintball sport so popular. The primary objective of this invention is to meet this need.  
     SUMMARY OF THE INVENTION  
      More specifically, an object of the invention is to provide a low pressure, low velocity projectile marker for youth shooting sports as an effective alternative to the sport of paintball.  
      Another object of the invention is to provide a projectile marker for youth shooting sports with a diminished impact as compared with traditional paintball. By combining a velocity of less than 150 feet per second (45 meters per second) with a greater impact surface area, impact from the projectile fired from the marker of this invention is safer and can be tolerated by youngsters wearing appropriate protective clothing.  
      An additional object of the invention is to provide a projectile marker capable of repeated reuse of a lightweight foam projectiles for youth shooting sports which, after shooting, may be recovered and recharged with a marking agent for repeated shots. This feature renders the equipment more economical for the youth market as compared with the expense associated with the traditional paintball sport.  
      Another object of the invention is to provide a projectile marker of the character described which includes an on-board air compressor. This eliminates the need for a separate pressure canister that must be removed from the marker and refilled from specialized, high pressure compressing equipment such as required for traditional paintball.  
      A further object of the invention is to provide an on-board air compressor of the character described which includes a hand activated pump with superior mechanical leverage to permit a youngster to compress a sufficient quantity of air into a storage reservoir so that the marker may be fired several times before re-pumping is necessary to recharge the supply reservoir.  
      Yet another object of the invention is to provide a pressure system for a projectile marker which prevents the user from exceeding a maximum pressure of approximately 150 psi (11 kg/cm 2 ).  
      Another object of the invention is to provide a removable barrel/magazine assembly to store a plurality of projectiles for seriatim firing from a marker. This permits combat players to carry a number of preloaded barrevmagazine assemblies onto a playing field to facilitate repeated firings and exchange of fresh barrel/magazine assemblies fully loaded with a supply of projectiles.  
      Another object of the invention is to provide a projectile marker of the character described which permits only seriatim firing of projectiles, rather than several projectiles being fired at once as is common with traditional paintball equipment.  
      An additional object of the invention is to provide a projectile marker of the character described with a sighting system through the marker that includes a line-of-sight substantially parallel with and above the cylindrical bore of the marker barrel.  
      A further object of the invention is to provide a projectile marker equipped with a removable barrel/magazine unit that visually indicates the number of projectiles remaining to be fired.  
      Another object of the invention is to provide a pressurized projectile marker having a number of safety features designed to reduce the risk of injury associated with pressure contained firing devices. Such features include a large cross sectional pressure conduit to disperse a pressure charge whenever the barrel/magazine assembly is not inserted into the marker; a twist lock to maintain the barrel/magazine assembly to the marker when correctly installed; and safety vent ports to harmlessly release a compressed air pulse in the event the barrel/magazine assembly is not correctly installed.  
      Yet another object of the invention is to provide a projectile marker of the character described having a trigger operated fire control valve to precisely release a controlled, momentary pulse of compressed air in order to discharge a projectile through the barrel of the marker.  
      In summary, a low pressure, low velocity projectile marker for youth shooting sports as an acceptable alternative to the traditional sport of paintball. The marker includes an onboard, hand activated pressure system to charge an air reservoir up to a maximum pressure of 150 psi (11 kg/cm 2 ) as limited by a pressure relief valve. A removable barrel/magazine assembly stores and visibly displays a plurality of projectiles. The barrel/magazine assembly is inserted and sealably locked into a pressure deliver conduit of the marker. A trigger mechanism operates a fire control valve to precisely release a controlled, momentary pulse of compressed air in order to discharge a single projectile through the barrel of the marker.  
      Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the detailed description of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the following description of the drawings, in which like reference numerals are employed to indicate like parts in the various views:  
       FIG. 1  is a side elevational view of a low velocity projectile marker constructed in accordance with a preferred embodiment of the invention, with the hand lever unlatched from the frame and moved partially forward to show a portion of the air pump;  
       FIG. 2  is a front elevational view of the marker;  
       FIG. 3  is a rear elevational view of the marker;  
       FIG. 4  is a side sectional view taken along line  4 - 4  of  FIG. 2  in the direction of the arrows;  
       FIG. 5  is an enlarged fragmentary view of an intake stroke of the air pump;  
       FIG. 6  is an enlarged fragmentary view of a compression stroke of the air pump;  
       FIG. 7  is an enlarged fragmentary view similar to  FIG. 6  but showing the pressure relief valve reacting to an excessive pressure condition within the air pump;  
       FIG. 8  is an enlarged fragmentary view of the internal air chamber interconnecting the air pump with the pressure reservoir;  
       FIG. 9  is an exploded, partially sectional view illustrating insertion of the barrel/magazine assembly into the pressure delivery conduit secured to the body frame of the marker;  
       FIG. 10  is an enlarge fragmentary view of the forward portion of the barrel/magazine assembly;  
       FIG. 11  is a fragmentary view of the barrel/magazine assembly inserted into the pressure delivery conduit but not yet locked in place;  
       FIG. 12  is a fragmentary view similar to that of  FIG. 11  but showing the barrel/magazine assembly twist locked onto the pressure delivery conduit;  
       FIG. 13  is a sectional view taken along line  13 - 13  of  FIG. 11  in the direction of the arrows;  
       FIG. 14  is a sectional view taken along line  14 - 14  of  FIG. 12  in the direction of the arrows;  
       FIG. 15  is an enlarged fragmentary composite view illustrating the trigger being partially squeezed and the fire control valve still closed, with the broken lines to indicate discontinuance in length of the fire control rod;  
       FIG. 16  is an enlarged fragmentary composite view similar to  FIG. 15  but illustrating the trigger being completely squeezed and the fire control valve momentarily opened; and  
       FIG. 17  is an enlarged fragmentary sectional view illustrating gas flow from the fire control valve to the firing chamber for propelling a projectile into the barrel of the marker. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      Referring to the drawings in greater detail, attention is first directed to  FIG. 1  illustrating a preferred embodiment of the invention. Generally, the projectile marker  20  includes a body frame  22  which carries the functional parts of the marker  20  including an air reservoir  24 , an air pressure system  26 , a barrel/magazine assembly  28 , and a trigger mechanism  30 , each of which will be described in detail.  
      The body frame  22  comprises two substantially similar shells  22   a  &amp;  22   b  ( FIGS. 2 &amp; 3 ) formed preferably from a durable, molded plastic. These similar shells  22   a  &amp;  22   b , therefore, provide a hollow housing when joined by screws (not shown), glue, sonic welding or similar connecting means along a central parting line  32  as shown in  FIGS. 2 &amp; 3 .  
      Securely fixed to the body frame  22  and slightly offset with respect to the central parting line  32  is an air reservoir  24 . The reservoir  24  is a sealed pressure tank  34  that may be of any convenient shape and size. The reservoir  24  illustrated in the drawings is contoured, shaped and sized to mimic the appearance of a hopper for a conventional paintball gun that holds a supply of paintballs for feeding to the paintball gun. As mentioned, however, the function of the reservoir  24  in the present invention is completely different from the paintball hopper of a conventional paintball gun. As shown in section in  FIG. 4 , the reservoir  24  includes a projection boss  36  on the forward end of the pressure tank in order to be received and held in place by a superstructure projection  38  of the body frame  22  extending above the barrel/magazine assembly  28 . In the lower region of the sealed tank portion of the reservoir is integrally formed a tubular fitting  40  ( FIG. 8 ) which provides access to the interior of the reservoir  24  which is otherwise sealed. The tubular fitting  40  is received by a socket projection  42  from the body frame  22  as shown in  FIG. 3 .  
      With reference to  FIGS. 2 &amp; 3 , it should be noted that the superstructure projection  38  has an open front sight therethrough. In the illustrated embodiment of the invention, the open front sight is an inverted triangle shaped tunnel  44  through the superstructure to aid in sighting the marker  20 . The rear sight on the marker  20  is formed as a V-shaped notch  46 . Thus constructed, the line-of sight, when the user aligns the tunnel  44  of the front sight in the V-notch  46  of the rear sight, is both parallel with and directly over the actual bore of the barrel/magazine assembly  28 .  
      Interiorly of the body frame  22  is housed the air pressure system  26 . The system  26  includes an air pump comprising a cylinder  50  fitted with a movable piston  52  on the end of an integral, longitudinally grooved piston rod  54  to slide back and forth within the cylinder  50 . One end of the cylinder  50  is closed and fitted with a check valve  56 , the details of which are best illustrated in  FIGS. 5 &amp; 6 . Generally, when the piston  52  slides back within the cylinder  50  during an intake stroke, ambient air fills the cylinder  50 . During the compression stroke, the piston  52  slides forward toward the closed end of the cylinder  50  and air under pressure flows through the check valve  56 .  
      The check valve  56  comprises in combination the closed end wall  58  of the cylinder  50 , a plurality of openings  60  through the closed end wall  58 , and a flexible circular seal gasket  62  which overlies the openings  60  on the outside of the cylinder end wall  58  and which is pinned to the end wall  58  by a retainer  64 . Accordingly, when air pressure within the cylinder  50  is greater than the pressure on the outside of the seal gasket  62  of the check valve  56 , the gasket  62  will flex to undercover the openings  60  in the end wall  58  of the cylinder  50  so that air flow from the interior of the cylinder  50  out through the openings  60 . This would be the case for a compression stroke of the piston  52  as illustrated in  FIG. 6 . Conversely, when air pressure on the outside of the seal gasket  62  of the check valve  56  is greater than the air pressure within the cylinder  50 , then the gasket  62  will seal against the openings  60  to block air flow therethrough. This would be the case for a intake or vacuum stroke of the piston  52  as illustrated in  FIG. 5 .  
      The piston  52  is slightly smaller in diameter than the inner diameter of the cylinder  50 . Cut in the outer circumference of the piston  52  is a tapered groove  66  which slopes inwardly toward the leading face of the piston  52 . That is to say that the diameter of the tapered groove  66  decreases from back to front as shown in  FIGS. 5 through 7 . Within the tapered groove  66  of the piston  52  is received an O-ring seal  68 . During an intake stroke of the piston  52  ( FIG. 5 ), therefore, the O-ring seal  68  moves within the tapered groove  66  toward the face of the piston  52  where the diameter of the groove  66  is smaller. Since the pressure within the cylinder  50  is slightly less than atmospheric pressure, ambient air flows through longitudinal grooves in the piston rod  54 , past the O-ring seal  68  and through openings  70  in the face of the piston  52  to the interior chamber of the cylinder  50  as illustrated by the gas flow arrows in  FIG. 5 . During an compression stroke of the piston  52  ( FIG. 6 ), on the other hand, the O-ring seal  68  moves within the tapered groove  66  away from the face of the piston  52  where the diameter of the groove  66  is larger. This causes the O-ring seal  68  to engage the inside surface of the cylinder  50  in a pressure tight fit so that the air within the cylinder  50  is compressed. When the pressure within the cylinder  50  is sufficiently greater than the pressure on the opposite side of the check valve  56 , the check valve  56  opens and air flows through the openings  60  in the end wall  58  of the cylinder  50  as illustrated by the gas flow arrows in  FIG. 6 .  
      To prevent over pressure conditions from developing, the piston  52  is equipped with a pressure relief valve  72 . Centrally positioned in a recess  74  in the face of the piston  52  is a central hollow bore  76  which extends into the piston rod  54 . Positioned in the bottom of the bore  76  is a spring  78 . A valve body  80  having an elongate lateral slot  82  therethrough is secured within the bore  76  by a cross pin  84  extending from the piston rod  54  through the lateral slot  82  of the valve body  80 . The valve body  80  includes circumferential groove  86  therein which receives an O-ring seal  88  to engage the interior wall of the bore  76 . So configured, the spring  78  within the bore  76  normally biases the valve body  80  toward the face of the piston  52  to the limit permitted by the cross pin  84  within the lateral slot  82  of the valve body  80  as shown in  FIG. 5  or  6 . In such position, the O-ring seal  88  carried on the valve body  80  creates a pressure resistant seal with the interior wall of the bore  76 . When sufficient pressure within the cylinder  50  is experienced, however, the pressure acts on the valve body  80  to move the valve body  80  within its bore  76  against the spring  78 . When the valve body  80  is compressed within its bore  76  a sufficient distance, as illustrated in  FIG. 7 , the valve body  80  uncovers a pressure relief bleeder hole  90  extending through the piston rod  54  and air flows from the interior of the cylinder  50 , through the bleeder hole  90 , and out through the longitudinal grooves in the piston rod  54  to atmospheric conditions. Once the pressure within the cylinder  50  returns to an acceptable value, then the spring  78  urges the valve body  80  forward to reseal the bleeder hole  90 . Those skilled in the physics will understand, therefore, that the maximum pressure within the cylinder  50  may be adjusted upwardly or downwardly as determined by a preselected spring constant for the spring  78  within the bore  76  of the pressure relief valve  72 .  
      In accordance with the objectives of this invention, the maximum pressure should never exceed 150 pounds per square inch (psi) or 10.5 kg/cm 2 . Experimentation has determined that the maximum pressure for the marker  20  may fall in the broad range of 10 to 150 psi (0.7 to 10.5 kg/cm 2 ) which is considered to be low pressure and is orders of magnitude less than the maximum pressure for conventional paintball guns considered to be high pressure devices. An effective range for the maximum pressure of the marker  20  of this invention is from 20 to 40 psi (1.4 to 2.8 kg/cm 2 ), but the most preferred range for the maximum pressure falls within 25 to 35 psi (1.8 to 2.5 kg/cm 2 ).  
      The onboard air pressure system  26  also includes a hand lever  92  connected to the piston rod  54  of the air pump. The lower end of the hand lever  92  forms a grip  94  from which a Y-shaped yoke  96  extends upwardly on each side of the body frame  22 . The upper ends of the yoke  96  are pivotally connected by pin  98  to the superstructure projection  38  of the body frame  22  extending above the barrel/magazine assembly  28 . Beneath the barrel/magazine assembly  28 , the body frame  22  includes a projection hook  100  to be engaged by a spring loaded latch  102  member carried in the grip portion  94  of the hand lever  92 . The latch  102  includes an elongate slot  104  throughwhich a pin  106  attached to the grip  94  extends to limit movement of the latch  102 . A spring  108  mounted within the grip portion  94  biases the latch  102  upwardly to catch behind the projection hook  100  when the lever  92  is positioned as shown in  FIG. 4 .  
      The latch  102  also includes an inclined cam surface  112  engaged by an angled surface  114  of a depressible release button  116  which projects from the grip  94 . When depressed, as shown in  FIG. 4 , the angled surface  114  of the release button  116  slides along the cam surface  112  of the latch  102  to cause the latch  102  to move downwardly against the force of the spring  108  to remove the latch  102  from behind the hook retainer  100  of the body frame  22 . When released, the opposite action occurs. The spring  108  moves the latch  102  upwardly, causing the cam surface  112  of the latch  102  to urge the release button  116  outwardly with respect to the grip  94 , and to cause the latch  102  to engage behind the projection hook  100  of the frame  22 .  
      The piston rod  54  from the air pump includes a cross piece  118  on the outer end thereof which is received by a pair of elongate sockets  120  within the hand lever  92 . With the release button  116  depressed, therefore, the hand lever  92  may be pivoted on the superstructure projection  38  of the body frame  22  and may be moved outwardly which causes the piston rod  54  to move the piston  52  of the air pump in an intake or vacuum stroke. At the outer limit of travel of the hand lever  92 , the grip  94  may then be pulled back to execute a compression stroke. This to and fro pumping action may be continued until sufficient air pressure is developed for operation of the marker  20 . By pivoting the hand lever  92  above the barrel/magazine assembly  28  as described, a youngster can achieve a superior mechanical leverage to permit sufficient compression of a quantity of air to a storage reservoir  24  so that the marker  20  may be fired several times before re-pumping is necessary to recharge the storage reservoir  24 .  
      Returning then to the internals of the air pressure system  26 , attention is again called to  FIG. 8 . The check valve  56  of the air pump is, in turn, connected to an internal air chamber  122 . The internal air chamber  122  may be of any convenient shape and volume within the body frame  22 . The air chamber  122  is equipped with a tubular fitting  1244  interconnected by tubing  126  to the tubular fitting  40  of the reservoir  24 . Thus, the internal air chamber  122  and reservoir  24  define a pressure sealed volume or space into which compressed air may be pumped through the check valve  56  by the air pump  26 . In the forward end thereof, the internal air chamber  122  is fitted with a valve seat  128  which is normally closed by a fire control valve  130  which will later be described in connection with the trigger mechanism  30 . The internal air chamber  122  is connected, through the valve seat  128  to a cylindrical receiver base  132 , as best illustrated in  FIG. 17 .  
      One end of an elongate, cylindrical pressure delivery conduit  134  is sealably connected to the receiver base  132  with an O-ring seal  136 . The pressure delivery conduit  134  is securely held in place by the body frame  22  engaging ridges  138  and ribs  140  formed on the outer cylindrical surface of the delivery conduit  134 . In the event the fire control valve  130  is opened, as shown in  FIG. 17 , then compressed air may be permitted to flow through the valve seat  128  of the internal air chamber  122  into the delivery conduit  134 . Otherwise, air flow is blocked by the fire control valve  130  as shown in  FIG. 8 .  
      Attention is next focused on the barrel/magazine assembly  28  with reference to  FIGS. 4, 9  &amp;  10 . The barrel  142  is a tubular section having a cylindrical bore  144  that substantially equals the cross sectional outer diameter the projectile  146  to be fired by the marker  20 .  
      The representative projectiles  146  illustrated in the drawings are spherical in form, but cone-shaped or bull-nosed projectiles may also be utilized without departing from the scope of this invention. Projectiles  146  suitable for use with the marker  20  of this invention are described our co-pending application Ser. No. 11/126,889, filed May 11, 2005 and entitled “Reusable Marker Projectile” which is incorporated herein by reference. In a spherical shape, the projectiles  146  are preferably in the range of 0.80 inches (20 mm) to 1.20 inches (30 mm) diameter which are substantially larger than conventional paintball at 0.689 inch (17.5 mm). Moreover, the projectiles  146  for use with the marker  20  of this invention are preferably formed of a synthetic molded foam to be fired at a velocity less than 150 feet per second (46 meters per second) which is approximate half the normal speed of a conventional paintball. Therefore, the size, shape, material and velocity all contribute to the goal of providing a projectile  146  for combat games which is less painful and has reduced safety risks than those associated with conventional paintball.  
      As shown in  FIG. 17 , at the innermost end of the barrel  142  is integrally formed a firing chamber  148  having a bore slightly less than the cross sectional outer diameter of a projectile  146  to be fired. For the spherical projectiles  146  as illustrated in the drawings, the firing chamber  148  is preferably formed as a truncated spherical seat  150  having a maximum diameter substantially equal to the outer diameter of the projectile  146  to be fired and a minimum diameter less than the outer diameter of the projectile  146  to be fired so that the projectile  146  engages the surface of the truncated spherical seat  150  in a gas tight relationship.  
      Influenced of course by several factors such as operating pressure of the marker  20 , as well as the resiliency of the material used for the projectiles  146 , the minimum diameter for the firing chamber  148  may range from approximately 80 to 90 percent of the diameter of the projectiles  146 . Through experimentation, the most preferred range for the minimum diameter of the firing chamber  148  is believed to fall in the range of 84 to 87% of the diameter of the projectiles  146 .  
      The firing chamber  148  is attached to an elongate tubular magazine  152  having first and second ends spaced apart sufficient distance to hold a quantity of projectiles  146  for seriatim delivery to the firing chamber  148 . The inside diameter of the tubular magazine  152  is slightly larger than the projectiles  146  to be fired so that the projectiles  146  may freely move within the magazine  152 . Near the second end of the tubular magazine  152 , a short flexible retainer or finger  154  extends into the passageway defined by the magazine  152 . The finger  154  is sufficiently flexible to permit projectiles  146  to be inserted into the second end of the magazine  152  and pushed past the flexible finger  154 . But it is also sufficiently rigid so as to prevent projectiles  146  within the magazine  152  from falling out through the second end of the magazine  152 .  
      At the connection between the first end of the tubular magazine  152  and the firing chamber  148 , a plurality of openings  156  extend through the wall of the magazine  152  to establish gas flow communication between the outside of the magazine  152  and the firing chamber  148 . The purpose of such openings  156  will become clear in the subsequent discussion explaining the interrelationship between the barrel/magazine assembly  28  and the pressure conduit  134 .  
      On the exterior wall of the firing chamber  148  is circumferential rib  158  having an outer diameter slightly less or equal to the inside diameter of the pressure conduit  134 . The circumferential rib  158  includes a groove or channel  160  therein to seat an O-ring seal  162 .  
      Just behind the openings  156  at the first end of the tubular magazine  152  is a circumferential band  164  which encircles a portion of the outer surface of the magazine  152 . The band  164  has secured thereto a pair of diametrically opposed seal pads  166  such that the diametric distance from the outer surface of one seal pad  166  to the other substantially equals the inside diameter of the pressure conduit  134 . The seal pads  166  are positioned around and held in place on the magazine  152  by bosses  168  projecting from the outer surface of the magazine  152  (see  FIGS. 13 &amp; 14 ).  
      With reference to  FIGS. 11 &amp; 12 , near the outer end of the barrel  142 , a pair of diametrically opposed ears  170  project from the outer surface of the barrel wall. A cylindrical muzzle  172  fits over the barrel  142  and is secured thereto by the ears  170  on the barrel  142  locking into corresponding notches  174  in the wall of the muzzle  172  by resiliently deformable fingers  176 . The forwardmost end of the muzzle  172  includes a plurality of lateral holes  178  therethrough to permit the escape of gas pressure in the event of an unexpected obstruction to the end of the muzzle  172 . The rearwardmost end of the muzzle  172  includes a pair of diametrically opposed keyways  180  to form a twist lock when registered with a corresponding pair of post projections  182  on the exterior wall of the pressure conduit  134 .  
      Referring again to  FIG. 17 , projecting from the receiver base  132  is a cylindrical pedestal  184  having an outer diameter substantially equal to the inside diameter of the tubular magazine  152 . Around the outer surface of the cylindrical pedestal  184  is a circumferential groove  186  which receives an O-ring seal  188 .  
      The barrel/magazine assembly  28  as previously described and as illustrated in  FIG. 9 , with a quantity of projectiles  146  loaded into the magazine  152 , may be inserted and installed in the pressure delivery conduit  134 . In doing so, the second end of the magazine  152  is inserted into the conduit  134  and pushed onto the cylindrical pedestal  184  of the receiver base  132  (see  FIG. 17 ). The O-ring seal  188  mounted on the pedestal  184  engages the interior cylindrical surface of the magazine  152  near the second end thereof to create a pressure seal. The barrel/magazine assembly  28  may be rotated within the delivery conduit  134  until the post projections  182  on the exterior wall of the pressure conduit  134  register with the keyways  180  on the muzzle  172  ( FIG. 11 ). With the barrel/magazine assembly  28  pushed into the pressure conduit  134  to the limit permitted by the keyways  180  receiving the post projections  182 , then barrel/magazine assembly  28  may then be twisted so that the post projections  182  are received in the lateral slots of the keyways  180  forming a twist lock arrangement to secure the assemble within the delivery conduit  134  ( FIG. 12 ). When installed as indicated, the seal pads  166  carried on the outer surface of the magazine  152  register with and seal the pressure relief ports  190  extending through the wall of the pressure delivery conduit  134 .  
      The pressure relief ports  190  of the delivery conduit  134  provide an important safety feature of the marker  20 . In the event the barrel/magazine assembly  28  is not twist locked as described onto the pressure conduit  134 , the relief ports  190  will be unsealed in order to dissipate pressure of any firing of the marker  20  ( FIGS. 11 &amp; 13 ). Otherwise, a faulty installation of the barrel/magazine assembly  28  to the pressure conduit  134  could cause the entire assembly  28  to be launched from the marker  20  rather than a projectile  146 .  
      When properly installed into the pressure delivery conduit  134 , the outer diameter of the tubular magazine  152  forms an annulus  192  with the inner diameter of the delivery conduit  134 .  
      The annulus  192  is in communication with the receiver base  132  opposite the fire control valve  130  such that compressed air through the control valve  130  is delivered to the annulus  192 , travels the length of the magazine  152  and passes through the openings  156  in the magazine  152  behind the firing chamber  148  to propel a projectile  146  in the firing chamber  148  into the barrel  142 , as illustrated with the gas flow arrows in  FIG. 17 . At the second end of the magazine  152 , air flow into the bore of the magazine  152  is prevented by the O-ring seal  188  between the pedestal  184  and the bore of the magazine  152 . At the first end of the magazine  152 , air flow is forced to the firing chamber  148  as a result of the pressure tight seal of O-ring  162  between the inner diameter of the pressure conduit  134  and the exterior wall of the firing chamber  148 .  
      Extending centrally through the pedestal of the receiver base  132  is a narrow rod  194  having a plunger head  196  on one end thereof. Supported within the body frame  22  is a tubular housing  198  which receives the opposite end of the rod  194 . An elongate coil spring  200  caged within the tubular housing  198  biases the rod  194  outwardly. So constructed the plunger head  196  and a portion of the rod  194  projects centrally into the magazine  152  to urge the projectiles  146  stored therein to seriatim engagement with the firing chamber  148 .  
      It is desirable that the pressure delivery conduit  134  and magazine  152  be fabricated of substantially transparent material. This enables the user to visually verify the number of projectiles  146  remaining in the magazine  152  and firing chamber  148 . Alternatively, the delivery conduit  134  and magazine  152  may be fabricated of opaque materials with strategically placed transparent windows therein so that the number of projectiles  146  remaining in the magazine  152  and firing chamber  148  can be ascertained by the user. Examples of such transparent windows  202  are illustrated in  FIG. 1  as being secured in openings through the body frame  22  in order to visually verify the presence of any projectiles  146  in that portion of the magazine  152  which extends into the body frame  22 .  
      Attention is next directed to the trigger mechanism  30  for the marker  20  with principal reference to  FIGS. 4, 15  &amp;  16 . A molded, depressible trigger  204  is slidably carried on the body frame  22  forming the handle portion  206  of the marker  20 . The trigger  204  includes a spring member  208  to bias the trigger  204  forward. The body frame  22  includes a safety pin  210  moveable to a “safe” position which prevents the trigger  204  from being depressed by engaging a catch  211 , and to a “fire” position which permits a user to squeeze the trigger  204  toward the handle  206  of the marker  20  and against the force of the biasing spring.  
      Interiorly of the body frame  22 , the trigger  204  includes a pawl  212  biased upwardly by a spring  214 . In alignment with but remote from the pawl  212  is cam wheel  216  mounted within the body frame  22  on a pivot post  218 . A leaf spring  220  encircles the pivot post  218  to hold the cam wheel  216  in the position as shown in  FIG. 4 . The lower portion of the cam wheel  216  includes a projection cog  222  which may be releasably engaged by the pawl  212  of the trigger  204  and the upper portion of the cam wheel  216  carries a striker hammer  224 . When the trigger  204  is initially squeezed to the handle  206  of the body frame  22 , the pawl  212  being biased upwardly by the spring  214  engages the cog  222  of the cam wheel  216 . Further squeezing of the trigger  204  causes the cam wheel  216  to rotate against and compress the leaf spring  220 . When the trigger  204  is completely squeezed to the handle  206 , the pawl  212  of the trigger  204  will disengage the cog  222  of the cam wheel  216  which has fully compressed the leaf spring  220 . No longer retained by the trigger pawl  212 , the cam wheel  216  under the influence of the leaf spring  220  whirls in the opposite direction (clockwise in  FIGS. 4, 15  &amp;  16 ) causing the striker hammer  224  of the cam wheel  216  to impact an anvil  226  positioned in alignment with rotation of the cam wheel  216 .  
      The anvil  226  is adjustably secured to a first end of an elongate fire control rod  228 . A threaded nut member  230  carried on the control rod  228  may be used to adjust the position of the anvil  226  with respect to the first end of the rod  228 . The opposite, second end of the rod  228 , fitted with an O-ring  232 , sealably penetrates the internal air chamber  122  and is connected to the fire control valve  130  normally closing the valve seat  128  between the internal air chamber  122  and the receiver base  132 . A spring  234  within the internal air chamber  122  acts to bias the fire control valve  130  to engagement with the valve seat  128  in order to block air flow through the valve seat  128  to the receiver base  132 .  
      However, when the cam wheel  216  is released by the trigger pawl  212  and whirls around with its striker hammer  224  impacting the anvil member  226 , the force of this blow to the anvil  226  temporarily dislodges the fire control valve  130  against its spring  234  bias to permit a momentary blast of compressed air to travel through the valve seat  128 . The amount of air delivered with each “shot” can be factory adjusted or fined tuned with the aid of the threaded member  230  to minutely change the location of the anvil  226  on the rod  228  connected to the fire control valve  130 .  
      In operation, therefore, the user will insure that a supply of appropriately sized projectiles  146  are loaded into the magazine  152  and that the barrel/magazine assembly  28  is properly installed to the pressure delivery conduit  134  of the marker  20 . The release button  116  on the hand lever  92  may be depressed to release the latch  102  and sufficient pumping strokes may be made to adequately pressurized the marker  20 . With the safety pin  210  moved to the “fire” position, the user squeezes the trigger  204  to fire a single projectile  146  one after another with each trigger pull so long as sufficient enough pressure remains stored the marker  20  for effective operation.  
      From the foregoing it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth, together with the other advantages which are obvious and which are inherent to the invention.  
      It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.  
      Since many possible embodiments may be made of the invention without departing from the scope thereof, it is understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.