GB2350667A - Air guns - Google Patents

Abstract

An air gun, in which a projectile is propelled by the medium of a compressed gas, has a reservoir 8 for the pressurised propellant gas chargeable from an external source of pressurised gas through a one-way valve 10. The reservoir 8 is also in communication with a bleed valve 24 adapted to relieve pressure in the reservoir 8 above a predetermined threshold value. This provides a consistent maximum reservoir pressure, aiding consistency of projectile velocity at that pressure, and thus the accuracy of shooting that can be attained. The reservoir 8 may also have gauge means 31 to give a visual indication of the pressure in the reservoir 8. The knock-off exhaust valve assembly 9 is arranged for closure by a piston 15 and provides a straight flow path for the gas leaving the reservoir 8. This also aids consistency of projectile velocity. The bleed valve 24 (figure 2, not shown), includes a valve rod (29) passing through an aperture in a neat and having a cylindrical portion for realing against the neat and tapered portion for allowing bleeding through the neat. Excess pressure pushes the rod against a spring so that the cylindrical portion is replaced in the neat by the tapered portion. The bleed valve also acts as a pressure indicator since the axial position of the rod depends on the reservoir pressure.

Description

2350667 IMPROVEMENTS IN AND RELATING TO AIR GUNS This invention relates to

air guns. The expression "air guns" is used herein in a broad sense and includes handguns (pistols) and shoulder-guns with rifled and unrifled barrels in which a projectile is propelled by the 5 medium of a compressed gas.

Air guns are generally divided into two classes according to their operating principle. On the one hand there are so-called spring guns in which a piston movable within a cylinder is cocked against a spring so that air is drawn into the cylinder, and in which, on triggered release of the piston, the air is driven from the cylinder into the breech of the gun; and on the other hand there are so-called pneumatic guns in which a gas is dispensed to the breech from a pre-charged pressurised reservoir.

The invention has particular reference to pneumatic guns, and also to a kit of parts which may be fitted to an existing gun such as a pneumatic gun, or to a spring gun whereby that spring gun may be converted to a pneumatic gun. It may also be used for guns which can use air cartridges instead of ordinary bullets.

Pneumatic guns generally have a substantial reservoir attached which may be pressurised to about 230 bar (3400 psi 23 MPa) and the compressed gas may be dosed therefrorn to provide propellant for up to about 250 shots. Various gases have been used as propellant, including CO, and nitrogen, but the usual propellant is compressed air. Conveniently sized portable bottles of compressed air are now widely available (and themselves rechargeable) thanks to the increased popularity of scuba diving, and accordingly the requirement for the gun-borne reservoir to have such a high capacity is reduced.

2 There is a problem in achieving a constant propellant energy input which is important for achieving a constant pellet velocity over a series of, for example, ten shots. It will be appreciated that a constant pellet velocity between shots is most desirable for consistently accurate target shooting.

It is known to provide a pneumatic gun with a pressure regulator chamber between the reservoir and the breech which is charged to a constant pressure (provided that the residual pressure in the reservoir is higher than that pressure) and which discharges at each shot.

Such systems give excellent consistency in the amount of propellant energy supplied, but they are expensive.

Accordingly, dosing of propellant is more usually effected by a springloaded trigger-operated hammer which operates a knock-off valve which is biased closed by a spring and which is also urged to the closed position by residual pressure within the reservoir. As a result, in a typical knock-off valve gun, when pressure in the reservoir is high, the opening time of the knock-off valve is short, but that time increases as the pressure in the reservoir drops as the charge becomes exhausted. This to some extent compensates for the drop in pressure in the reservoir and in consequence it is usually found that, during a single charge-life of a reservoir, muzzle velocity initially increases, then levels out and finally drops to a level where recharging becomes necessary. There is thus typically an optimum reservoir pressure for any particular knock-off valve gun. This optimum pressure will vary according to several factors, not the least important of which is the calibre of the gun.

According to a first aspect of the present invention, there is provided an air gun having a reservoir adapted to contain pressurised propellant gas which is chargeable from an external source of pressurised gas via a one3 way valve and which is in communication with a bleed valve adapted to relieve pressure within the reservoir above a predetermined threshold pressure value.

The predetermined pressure threshold can be set at or about an optimum reservoir pressure thus enabling a well-defined propellant energy supply to the pellet and promoting consistency of pellet velocity over a series of shots.

The threshold value of pressure to which the bleed valve effectively limits pressurisation of the reservoir may be preset by the gunmaker to an optimum value for that particular model of gun. That value may for example have been established on the basis of tests on that model as being a pressure at the upper end of a pressure range over which pellet velocity variations are small.

In some embodiments of the invention, the bleed valve is adjustable whereby said threshold pressure value may be varied. This will allow the owner of any particular gun to "tune" the gun. The bleed valve comprises a one-way valve, and a further aspect of the invention is concerned with this. However, a second aspect of the invention is concerned with indicating the pressure in the reservoir.

In its second aspect, the present invention provides an air gun having a reservoir adapted to contain pressurised propellant gas which is chargeable from an external source of pressurised gas via a one-way valve and which is in communication with gauge means adapted to give a visual indication of pressure within the reservoir.

Such gauge means does not need to be a dial gauge, though it could be: a simple pin projecting from a housing can be quite sufficient to give the 4 desired indication of reservoir pressure to the shooter.

For example, as provided by some preferred embodiments, the arrangement could be such that a distal end of the pin lies flush with its housing when the reservoir pressure is at the lower end of a predetermined pressure range. It could thus provide a visual indication to the shooter that the reservoir should be recharged if it was desired to continue operating in an optimum reservoir pressure range.

Alternatively, or in addition, the pin could carry a marking part way along its length which corresponds to a reservoir pressure at the upper end of a predetermined pressure range. For example a proximal portion of the pin could be coloured red. The appearance of any red portion of the pin outside its housing could be arranged to correspond with a threshold value at the upper end of an optimal reservoir pressure range.

Particularly preferred embodiments of the invention combine the first and second aspects. The incorporation of a said bleed valve allows the reservoir automatically to be charged to a threshold pressure at the upper end of a predetermined pressure range. The use of a separate gauge means having a marking corresponding to that threshold pressure allows an adjustable bleed valve to be returned to that threshold pressure after any adjustment should that be desired, and can also give an indication that such an adjustment has been made.

Another factor which affects the propellant energy input and thus the pellet velocity and accuracy is the flow path of the propellant gas from the reservoir to the breech.

In a conventional knock-off valve pneumatic gun, the spring-loaded hammer flies forwards, parallel to the axis of the barrel, to impact against a stem of an exhaust valve seated in the rearward end of the reservoir. The valve body is knocked off its seat against the bias of a coil spring within the reservoir and gas is exhausted. After the initial impact of the hammer on the valve stem, the valve is urged back to its seat by the coil spring and is held there by that spring and the internal gas pressure in the reservoir until the next shot. The propellant gas is exhausted backwards past the valve stem to a transverse port and thence to the breech. The propellant gas thus follows a U-shaped path. Such a gas-flow path is not efficient in the use of air and may entail a lack of consistency of propellant energy which is supplied to the breech of the gun.

An alternative arrangement is used in air cartridge guns, where the gas is exhausted from the forward end of the reservoir, by a valve seated inside the forward end of the reservoir. The valve is pulled off its seating on operation of the hammer, but is then unbalanced and the pressure in the reservoir then acts to keep the valve open, so that it does not close again until the reservoir pressure drops to atmospheric pressure. The whole reservoir is therefore emptied each time the valve opens. Furthermore, the higher the reservoir pressure, the further the valve moves away from its seat, which is the opposite of what is required, as explained above. Another disadvantage is the need to pull the valve off its seat, which entails a different and more complex mechanical arrangement between the hammer and the valve in comparison with the conventional pneumatic gun.

In its third aspect therefore, the present invention provides an air gun having a reservoir adapted to contain pressurised propellant gas which is dischargeable through a knock-off exhaust valve assembly operable by a trigger-actuated hammer in which the reservoir and valve assembly comprises a pressure vessel having a charging valve, and an external exhaust valve seat towards a forward end thereof communicating with a 6 generally forwardly extending exhaust port, an exhaust valve member seatable on the external exhaust valve seat and having a _valve stem extending rearwardly through the pressure vessel to a piston sliding in sealing engagement with a cylinder formed at the rearward end of the pressure vessel where the piston is exposed for striking by the hammer, wherein the piston is urged rearwardly by closure spring means, and the effective area of the exhaust valve member in the closed position, which is exposed to gas pressure in the pressure vessel to urge it in the valve opening direction, is less than the effective area of the piston which is exposed to gas pressure in the pressure vessel urging the exhaust valve member in the valve closing direction, so that when opened, the exhaust valve tends to return to sealing engagement with the seat under the influence of the gas pressure acting on the piston.

The provision of the exhaust valve seat external to the reservoir and the piston in the reservoir enables the exhaust port to be at the forward end of the reservoir, so that the gas-flow path can be much straighter to ensure efficiency and consistency, while enabling the exhaust valve to be operated in the same way as the conventional knock-off valve, in that it is pushed rather than pulled off its scat. The reservoir pressure acting on the piston pulls the exhaust valve member back onto its seat, so that the valve operation is controlled.

The arrangement also ensures that the exhaust valve is driven further off its seat as the reservoir pressure reduces, so increasing the volume of air exhausted, as required. The relative areas of the exhaust valve member and the piston are arranged so that the exhaust valve member is unseated easily. Because in the closed position the exhaust valve is counterbalanced by the piston, it can actually have a relatively large area, allowing better gas flow and providing strength for reliability.

7 The closure spring means also assists in seating the valve in operation, but its principal function is to ensure that the exhaust valve remains closed while the reservoir is being charged. The closure spring means preferably comprises a coil spring. Preferably the pressure vessel includes a constriction surrounding the valve stem which provides a shoulder for the valve closure spring.

The gun may be a breaking gun which is closable so that the breech end of its barrel is in register with the forward end of the exhaust port. Alternatively, it could be of the fixed barrel type.

In at least the most preferred embodiments of the invention in its third aspect, the flow path of gas from the reservoir to the breech is simplified, and it continues in a generally forward direction. This aspect of the invention thus enables any U-turn in the gas flow path to be avoided with a consequently improved consistency in propellant energy supplied.

In its fourth aspect, the invention provides a kit of parts for incorporation into an existing gun to provide a reservoir adapted to contain pressurised propellant gas dischargeable through a knock-off exhaust valve assembly operable by a trigger- actuated hammer, the reservoir and exhaust valve assembly comprising a pressure vessel having a charging valve, and an external exhaust valve seat towards a forward end thereof communicating with a generally forwardly extending exhaust port, an exhaust valve member seatable on that external valve seat and a stem for the exhaust valve which is adapted to extend rearwardly through the pressure vessel to a piston which is adapted to slide in sealing engagement with a cylinder formed at the rearward end of the pressure vessel where the piston is exposed for striking by a hammer, wherein the kit includes closure spring means adapted to urge the piston rearwardly, and the effective area of the exhaust valve member in the closed position, which is exposed to gas 8 pressure within the pressure vessel to urge it in the valve opening direction, is less than the effective area of the piston which is-exposed to gas pressure in the pressure vessel urging the exhaust valve member in the valve closing direction, so that when opened, the exhaust valve tends to return to sealing engagement with its seat under the influence of the gas pressure acting on the piston.

Such a kit of parts may be constructed to a size and design which will allow it to be substituted into the operating mechanism of an existing pneumatic gun, or to be used as an air cartridge for a conventional gun.

In preferred embodiments of the fourth aspect of the invention, such kit further includes a hammer and a hammer spring. A kit having these further parts may be constructed to a size and design which will allow it to be substituted into the operating mechanism of an existing spring gun to convert that spring gun into a pneumatic gun.

The invention extends to fifth and sixth respective aspects as follows:

a kit of parts for incorporation into an existing gun which has a pressure vessel with a one-way charging valve, and an exhaust valve having a stem which is adapted for striking by a hammer, wherein the kit includes a bleed valve for the pressure vessel, the bleed valve being adapted to operate to relieve pressure within the pressure vessel which exceeds a predetermined threshold pressure value; and to a kit of parts for incorporation into an existing gun which has a pressure vessel with a one-way charging valve, and an exhaust valve having a stem which is adapted for striking by a hammer, wherein the kit includes pressure indicating gauge means which is adapted to be fitted to the pressure vessel.

9 A kit of parts in accordance with the invention may incorporate a combination of any two or, and preferably, all three of the fourth, fifth and sixth aspects of the invention.

Yet another aspect of the present invention relates to a one-way valve adapted to be used in conjunction with air guns. A one-way valve may be used as a bleed valve in accordance with the first aspect of the invention, or as an inlet valve when a gun-borne reservoir is charged from an external source. Conventional one-way valves used in air guns comprise a spring-loaded ball valve member co-operating with a valve seat. The valve opens when the force due to the pressure acting on the ball exceeds the opposing force exerted by the spring. These valves work well, but at the high gas pressures involved, open quickly and abruptly.

According to a seventh aspect of the invention, a one-way valve adapted for use in conjunction with an air gun comprises a spring-loaded valve member sliding in an aperture in a valve seating member, the valve member having a first portion whose cross-sectional area corresponds to that of the aperture so that the first portion seals against the aperture to close the valve, and a second portion whose cross-sectional area gradually reduces to provide a gradual opening of the valve as the second portion moves through the aperture.

Providing a gradual opening ensures that the valve operates smoothly.

Preferably the aperture is cylindrical and the valve member a solid tapered rod. The tapered rod may be carried by a stepped rod, the two rods forming the valve member. The seating member may be of PTFE, or any other suitable material.

The one-way valve may be used as a bleed valve in accordance with the first aspect of the invention, or as an inlet valve for charging a gunborne reservoir from an external source.

A preferred embodiment illustrating all aspects of the invention, will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal cross-section through the operating mechanism of an air gun of pneumatic type; and Figure 2 shows a one-way valve of the mechanism in greater detail.

In Figure 1 of the drawings a receiver of an air gun is generally indicated at 1 and it carries a trigger 2 which is arranged to hold a sear 3 which in turn engages with a hammer 4 to prevent that hammer from being urged in a forward direction 5 by a hammer spring 6 until the sear is released on pulling of the trigger 2.

The receiver includes a pressure vessel 7 adapted to contain a reservoir 8 of pressurised propellant gas which is dischargeable through a knock-off exhaust valve 9 operable by the trigger- actuated hammer 4. The pressure vessel 7 has a charging valve 10, a pressure relief bleed valve 24 and an external exhaust valve seat 11 towards a forward end 12 thereof communicating with a generally forwardly extending exhaust port 13.

The exhaust valve member 9 is seatable on the external valve seat 11 and is carried by a valve stem 14 extending rearwardly through the pressure vessel 7 to a piston 15 sliding in sealing engagement with a cylinder 16 formed at the rearward end 17 of the pressure vessel 7. At that rearward end 17, the piston is exposed, via an anvil 18, and a striking block 19 for 11 striking by the hammer 4 on its release by the trigger 2. The piston 15 is urged rearwardly by a relatively light closure coil spring 20 which bears against a shoulder 21 formed by a rearward face of a constriction 22 in the pressure vessel. The effective area of the exhaust valve member 9 exposed to gas pressure within the pressure vessel 7 tending to urge that member 9 with piston 15 and their interconnecting valve stem 14 in the valve opening direction (5) is less than the effective area of the piston 15 exposed to the gas pressure within the pressure vessel 7 urging those parts 9, 14, 15 in the valve closing direction. Operation of the hammer 4 thus acts on the piston 15 to open the exhaust valve 9 to allow gas from the reservoir 8 to pass into the exhaust port 13. It will be appreciated that the gas follows a substantially linear path from the exhaust valve 9. After striking by the hammer 4 the exhaust valve 9 returns to sealing engagement with its seat 11 under the influence of the differential forces acting on the piston 15. The closure spring 20 does assist this action, but its principal function is to ensure that the valve 9 remains closed when the vessel 7 is charged.

The constriction 22 in the pressure vessel 7 is formed by a thickening of its wall into which is threaded the one-way inlet valve 10 of the reservoir 8. In fact, the constriction is formed by a rearward end piece 23 of the pressure vessel which is also machined to form the cylinder 16 and a portway for a pressure relief bleed valve 24.

Figure 2 shows the bleed valve 24 in detail. The valve 24 is a one-way valve, but instead of the usual spring-biassed ball valve member it comprises a piston 25 biassed by a spring 27 and sliding in a cylinder 26 in a cap 28. The piston 25 comprises a solid tapered rod 29 forced into a blind bore 30 in a stepped rod 31. The outer end of rod 31 projects through an aperture in the cap 28, while the spring 27 acts between the cap 28 and the larger diameter inner end of the rod 31. The rod 29 forms 12 the valve member, sliding in a circular aperture 32 in an annular valve seating member 33 of PTFE or other suitable material -held in a substantially cup-shaped member 37. The member 37 is of brass and has a central aperture 38 through which the rod 29 passes. An 0-ring 34 seals between the member 37 and the outer diameter of the seating member 33. The rod 29 has a first portion 29a whose cross-sectional area corresponds to that of the aperture 32 and which in the closed position shown seals against the member 33. The rod 29 has a second portion 29b whose cross-sectional area tapers towards its inner end, so that movement of the rod 29 outwardly gradually opens the valve as the second portion moves through the aperture 32. At its inner end the rod 29 is exposed to the interior of the pressure vessel 7, and accordingly, on charging via inlet valve 20, the rods 29 and 31 move outwardly against the bias of the spring 27.

The valve 24 thus opens gradually to allow gas to be relieved from the pressure vessel 7. The pressure required to open the valve 24 represents a threshold pressure above which the pressure vessel cannot be charged.

The geometry of the valve 24 and the strength of the coil spring 27 are chosen so that the threshold pressure represents the upper end of an optimum range of pressures for the particular gun or model of gun concerned. At the threshold pressure the distal end of the rod 31 projects out of the cap 28. As shown, the threshold pressure is set by the gun maker, and is not adjustable by the user, but in a modification (not shown) the threshold pressure may be adjustable.

The length of the piston rod 31 is chosen so that its distal end is flush with the surface of the cap 28 when the pressure within the pressure vessel 7 is at the lower end of an optimum range of pressures for the particular gun or model of gun concerned. The rod 31 therefore acts as 13 a gauge giving a visual indication of the pressure in the pressure vessel 7. It may carry markings, such as coloured bands, to indicate the pressure.

The striker block 19 may be, and preferably is, as shown, an anti-bounce 5 shuttle device as described and illustrated in International Patent Publication No WO 98/23912.

At the forward end of the action 1 is shown a flange 35 pierced with holes 36 for retaining pins for a hinge (not shown) of a barrel. The arrangement is such that the barrel can be broken away from the action at the forward end of the exhaust port for the insertion of a pellet or other missile into the breech end of the barrel with the gun then being closable so that the barrel lies parallel with the forward direction indicated by the arrow 5 and with its breech in register with the forward end of that exhaust port 13.

It will readily be appreciated that the essential elements of the present invention as illustrated could readily be redesigned and adapted to fit an existing action of an air gun which did not incorporate those features, whether that existing gun was of pneumatic or spring type.

It will also be appreciated that kits of parts can be provided as substitutes for or in addition to the actions of existing air guns. Thus, a kit of parts is envisaged to provide the reservoir and exhaust valve assembly as shown. A second kit of parts can provide the bleed valve for the pressure vessel, while a third kit can provide the pressure indicating means for the pressure vessel. Naturally, one or more of these kits can be combined as appropriate.

Claims (23)

14 CLAIMS

1. An air gun including a reservoir adapted to contain pressurised propellant gas which is chargeable from an external source of pressurised gas via a one-way valve, and which is in communication with a bleed valve adapted to relieve pressure within the reservoir above a predetermined threshold pressure valve.

2. An air gun as claimed in claim 1, in which the threshold pressure value to which the bleed valve limits pressurisation of the reservoir is fixed.

3. An air gun as claimed in claim 1, in which the bleed valve is adjustable to vary the threshold pressure value.

4. An air gun as claimed in any preceding claim, in which the bleed valve comprises a one-way valve.

5. An air gun as claimed in claim 4, in which the bleed valve comprises a spring-loaded valve member sliding in an aperture in a valve seating member, the valve member having a first portion whose crosssectional area corresponds to that of the aperture so that the first portion seals against the aperture to close the valve, and a second portion whose cross-sectional area gradually reduces to provide a gradual opening of the valve as the second portion moves through the aperture.

6. An air gun including a reservoir, adapted to -contain pressurised propellant gas which is chargeable from an external source of pressurised gas via a one-way valve, and which is in communication with gauge means adapted to give a visual indication of pressure within the reservoir.

7. An air gun as claimed in claim 6, in which the gauge means comprises a dial gauge.

8. An air gun as claimed in claim 6, in which the gauge means comprises a pin projecting from a housing.

9. An air gun as claimed in claim 8, in which a distal end of the pin lies flush with the housing when the reservoir pressure is at the lower end of a predetermined pressure range.

10. An air gun as claimed in claim 8 or claim 9, in which the pin carries a marking part way along its length which corresponds to a reservoir pressure at the upper end of a predetermined pressure range.

11. An air gun including a reservoir adapted to contain pressurised propellant gas which is dischargeable through a knock-off exhaust valve assembly operable by a trigger- actuated hammer, in which the reservoir and exhaust valve assembly comprises a pressure vessel having a charging valve, and an external exhaust valve seat towards a forward end thereof communicating with a generally forwardly extending exhaust port, an exhaust valve member seatable on the external exhaust valve scat and having a valve stem extending rearwardly through the pressure vessel to a piston sliding in sealing engagement with a cylinder formed at the rearward end of the pressure vessel where the piston is exposed for striking by the hammer, wherein the piston is urged rearwardly by closure spring means, and the effective area of the exhaust valve member in the closed position, which is exposed to gas pressure in the pressure vessel to urge it in the valve opening direction, is legs than the effective area of the piston which is exposed to gas pressure in the pressure vessel urging the exhaust valve member in the valve closing direction, so that when opened, the exhaust valve tends to return to sealing engagement with the seat under the influence of the gas pressure acting on the piston.

16

12. An air gun as claimed in claim 11, in which the closure spring means comprises a coil spring acting between the piston, and a shoulder surrounding the valve stem.

13. A kit of parts for incorporation into an existing gun, to provide a reservoir adapted to contain pressurised propellant gas dischargeable through a knock-off exhaust valve assembly operable by a trigger- actuated hammer, the reservoir and exhaust valve assembly comprising a pressure vessel having a charging valve, and an external exhaust valve seat towards a forward end thereof communicating with a generally forwardly extending exhaust port, an exhaust valve member seatable on that external valve seat and a stem for the exhaust valve which is adapted to extend rearwardly through the pressure vessel to a piston which is adapted to slide in sealing engagement with a cylinder formed at the rearward end of the pressure vessel where the piston is exposed for striking by a hammer, wherein the kit includes closure spring means adapted to urge the piston rearwardly, and the effective area of the exhaust valve member in the closed position, which is exposed to gas pressure within the pressure vessel to urge it in the valve opening direction, is less than the effective area of the piston which is exposed to gas pressure in the pressure vessel urging the exhaust valve member in the valve closing direction, so that when opened, the exhaust valve tends to return to sealing engagement with its seat under the influence of the gas pressure acting on the piston.

14. A kit as claimed in claim 13, including a hammer and a hammer spring.

15. A kit of parts for incorporation into an existing gun having a pressure vessel with a one-way charging valve and an exhaust valve having a stem which is adapted for striking by a hammer, the kit including a bleed valve for the pressure vessel, the bleed valve being 17 adapted to operate to relieve pressure within the pressure vessel which exceeds a predetermined threshold pressure value.

16. A kit of parts for incorporation into an existing gun which has a pressure vessel with a one-way charging valve, and an exhaust valve having a stem which is adapted for striking by a hammer, the kit including pressure indicating gauge means which is adapted to be fitted to the pressure vessel.

17. A one-way valve adapted for use in conjunction with an air gun, comprising a spring-loaded valve member sliding in an aperture in a valve seating member, the valve member having a first portion whose crosssectional area corresponds to that of the aperture so that the first portion seals against the aperture to close the valve, and a second portion whose cross-sectional area gradually reduces to provide a gradual opening of the valve as the second portion moves through the aperture.

18. A one-way valve as claimed in claim 17, in which the aperture is cylindrical.

19. A one-way valve as claimed in claim 17 or claim 18, in which the valve member comprises a solid tapered rod.

20. A one-way valve as claimed in claim 19, in which the tapered rod is carried by a stepped rod, the two rods forming the valve member.

21. A one-way valve as claimed in any of claims 17 to 20, in which the seating member is of PTFE.

22. An air gun substantially as described herein with reference to and as illustrated in the accompanying drawings.

23. A one-way valve for use in conjunction with an air gun 18 substantially as described herein with reference to and as illustrated in the accompanying drawings. -