US Classes124/71, With control for discharge of fluid pressure124/72For continual projection of successive projectiles (e.g., for "rapid fire", etc.)
Attorney, Agent or Firm
International ClassF41B 11/00
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' 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 (CO2) 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/cm2). Typical operating pressures range from about 450 to 900 psi (32 to 63 kg/cm2). 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/cm2).
 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/cm2) 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 22a & 22b (FIGS. 2 & 3) formed preferably from a durable, molded plastic. These similar shells 22a & 22b, 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 & 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 & 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 & 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/cm2. 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/cm2) 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/cm2), but the most preferred range for the maximum pressure falls within 25 to 35 psi (1.8 to 2.5 kg/cm2).
 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 & 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 & 14).
 With reference to FIGS. 11 & 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 & 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 & 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 & 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.