GB2192046A

GB2192046A - Compressed gas cartridge

Info

Publication number: GB2192046A
Application number: GB8708693A
Authority: GB
Inventors: Antony John Allen Bubb
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-04-23
Filing date: 1987-04-10
Publication date: 1987-12-31
Anticipated expiration: 2007-04-10
Also published as: GB8708693D0; GB2192046B

Abstract

A compressed gas cartridge to be fired in an air gun has an outer casing 100 and a valve member 102 extending therein to seal apertures at both ends of the casing (but axially displaceable at the discharge end to propel a missile 118 by means of a firing lever 116). The apertures sealed are of unequal area so that a resultant force on the valve member due to gas pressure within the cartridge seals the valve head 102A against the valve seat 105 to. The cartridge may be charged through the discharge end by means of a union (120) coupled to the source of compressed gas which retains the valve member 102 at the discharge end against movement whilst allowing the casing to slide relatively to the union. By appropriately biasing the casing, the movement thereof is effective to impart a non-return action to the discharge valve of the cartridge. In a gun for firing the cartridge the lever 116 is coupled to a toggle linkage formed by trigger 141 and links 143 which in an overcentre position transmits force with substantial mechanical advantage. The lever 116 and toggle form a trapezium linkage which allows rearward pivoting of the lever to free the cartridge chamber. <IMAGE>

Description

SPECIFICATION Improvements in and relating to air guns This invention concerns improvements in and relating to air guns, and more particularly to rechargeable air or gas cartridges for use with air guns.

As is well known, pneumatic and gas-operated air guns, as opposed to spring powered air guns, derive the energy required for discharge of a pellet or missile by releasing a measure of compressed air or gas from a reservoir which has been precharged with air or gas at high pressure. Such reservoirs are conventionally built into the air gun, although it has been proposed to provide interchangeable reservoirs which can be loaded into a gun together with the pellet or missile to be discharged in the manner of the explosive cartridge of a firearm. Such proposals were first made in the late 19th century, although it was not until recent years that so-called air cartridges have become commercially successful.

To the knowledge of the present applicant, only one company is currently engaged in the commercial production of such air cartridges, and thus the current state of the art may be summarised as comprising the eariy proposals referred to above, and the more recent developments of the company concerned. For a review of the early state of the art, reference may be made to United Kingdom Patent Specification No. 1601918. Later developments, not all of which appear to have proved commercially practicable, are described in EP 87883, EP 100612 and GB 1601917, 2124346, 2153983, 2154308, 2154714 and 2170300. Not all of the publications referred to were available prior to the priority date of the present application, and thus the state of the art referred to includes that in accordance with Section 2 (3) of the Patents Act 1977.

Despite the above-mentioned developments in air cartridges, the known constructions remain relatively expensive to produce, and thus the cost of commercially available cartridges is such that it is uneconomic for the average user of a cartridge-powered air gun to purchase more than a limited number of rechargeable air cartridges, which considerably reduces the attraction of the cartridge actuated weapon in comparison with that of the conventional air gun. Also the known systems have proved difficult to charge with compressed gas in such a manner that a consistent power output is obtained, which is a primary requirement to achieve accuracy of the associated air weapon.

Accordingly, it is believed that a simple and inexpensive rechargeable air cartridge would represent a considerable advance in the art and expand the commercial development of the cartridge actuated weapon in comparison with conventional spring-actuated or pneumatic air weapons. A further advance would be the provision of means enabling consistent charging of such a cartridge to a constant internal air pressure.

It is accordingly an object of the present invention to provide an improved air cartridge.

It is a further object of the invention to provide an improved means for charging such cartridges.

The invention, in the sense of the monopoly sought by the applicant in the light of the state of the art currently known to him, will be apparent from the accompanying Claims.

However, one skilled in the art and fully aware of the true state of the art as existing at the priority date of the present application may recognise from the accompanying description a novel concept embodying an inventive step and having an application not comprehended within the scope of the monopoly defined in the accompanying Claims. To the extent that such a disclosure would support Claims to an alternative monopoly, it is intended that the present application shall form a basis for a claim to any such monopoly, either in the present application, or in an application filed in accordance with Section 15 (4) of the Patents Act 1977.

The invention is illustrated by way of example in the accompanying drawings, in which; Figure 1 is a sectional elevation of an air cartridge in accordance with the invention, Figure 2 is a similar view of a cartridge as shown in Fig. 1, when in place in an apparatus for charging the cartridge with compressed gas, Figure 3 is a view similar to Fig. 1 of another embodiment of the invention, Figure 4 is a view similar to Fig. 1, illustrating a further embodiment of air cartridge in accordance with the invention, shown in place in a diagrammatically illustrated air weapon, Figure 5 is a view corresponding to Fig. 4 showing the firing mechanism of the air weapon in the position for loading and unloading of a cartridge, Figure 6 is a view of the cartridge shown in Fig. 4, when in place in a pump in accordance with the invention adapted to enable charging thereof, and Figure 7 is a fragmentary view corresponding to Fig. 4 showing a modified arrangement of the front end of the cartridge.

From the following decription, it will be appreciated that the cartridges of Figs. 1 and 3 on the one hand, and Figs. 4, 5 and 7 on the other hand both incorporate the same inventive concept. However, the former has the general configuration of a cartridge as described in Swiss Patent Specification No.

16072 of 1898, in that the cartridge is fired by impact on a forwardly driveable valve member from the rear of the cartridge, and the latter operates according to the general principal of German Patent Specification No.

119323 of 1899, in that the cartridge is fired as a result of the release of the valve member by means of a hollow abutment that penetrates the forward end of the cartridge.

Referring to Fig. 1 of the drawings, the cartridge comprises a generally cylindrical outer casing 1, formed as two mating screw threaded portions 1 A, 1 B, the forward portion IA of which receives as a sliding fit a tubular member 2 of a material such as nylon that is capable of forming a seal. The member 2 is capable of receiving therein an air-gun pellet 3. A valve member 4 is rectilinearly slidable within the outer casing 1 and comprises a rear portion 5 sealed within the cylindrical bore of the casing 1 by means of an 0-ring 6.

The piston portion 5 is connected to a valve head 7 by means of a stem 8.

The valve head 7 engages a valve seat 9 formed by a ring of resilient material housed within the casing 1. The ring 9 has an internal diameter smaller than that of the valve head 7, but is sufficiently resilient to be passed over the valve head 7 when in the free state.

However, it prevents the valve head 7 from being drawn back through it by the forces on the valve member, in use, when constrained by the casing 1. The ring 9 is held in place in the casing 1 by a sliding sleeve 10 of rigid material biased by a compression spring 11.

The internal diameter of the sleeve 10 is sufficiently great to allow passage of the valve head 7. The screw thread between the two portions 1A, 1B of the housing 1 is sealed in a suitable manner, for example by p.t.f.e. sealing tape placed between the threads at the time of assembly, so that the housing 1, in conjunction with the valve member 7 forms a gas-tight enclosure capable of being charged to high pressure for example in excess of 100 bar.

The operation of the cartridge is as follows.

When the volume enclosed between the casing 1, the piston portion 5 and the valve head 7 is charged to a high air pressure, the valve will be biased to the closed position by a force F, which is defined by the formula: F, =P(A,-A2} Where P=air pressure within the casing; A,=cross sectional area of the casing portion containing piston portion 5; and A2=effective cross sectional area of the opening to valve seat 9.

By appropriate selection of these parameters it can therefore be arranged that with a desired internal pressure P the force on the valve member 4 has a magnitude sufficient to maintain a seal at the valve seat 9 whilst being sufficiently low to enable the valve to be opened by impact or pressure upon the exposed rear face of the piston portion 5, as by a member the equivalent of a firing pin.

When the cartridge is inserted in the chamber of an airgun with the front face of the member 2 in engagement with a counter surface surrounding the bore of the airgun barrel, forward pressure or impact upon the piston portion 5 will move the valve member 4 forwardly relatively to the casing 1 thus opening the discharge port defined by the valve seat 9. It will be noted that in comparison with the conventional knock-off valve, the valve head 7 is on the downstream rather than the upstream side of the discharge port and thus the pressure drop across the valve head 7 due to the speed of air flow through the discharge port and the drag coefficient of the valve is such as to produce a force aiding rather than opposing the opening of the valve member 4.

The dynamic forces acting upon the valve member 4 in the opening phase will therefore be relatively complicated since the closing force in the static condition will be modified to the extent that the pressure drop across the valve head 7 varies as air is discharged from the cartridge. Suffice it to say that initial experiments have shown that a hammer mechanism similar to that used for actuating a conventional knock-off valve of a pneumatic air gun will also serve to actuate a cartridge in accordance with the invention.

Referring to Fig. 2 of the drawings, there is shown in diagrammatic form a means for charging the cartridge of Fig. 1 with compressed air. The device, may for example, comprise a piston and cylinder 20, 21 actuated by a pump mechanism of known construction having a socket 22 within which the spigot at the forward end of the casing 1A can be received as a sliding fit, being sealed by means of an 0-ring 23. The casing 1 can be retained in engagement with the socket 22 by means of an outer end cap arrangement 24 arranged for releasable engagement with the end of the cylinder 21, for example by means of an bayonet joint indicated diagrammatically at 25.Within the end cap 24 is fixed a pillar 25 having a free end 25A that is stepped to define a portion of smaller diameter than the end 5 of the valve 4, and a portion of larger diameter, so that whilst the valve 4 is retained in a forward position by abutment with the smaller diameter portion of the pillar 25, the casing 1 is free to move rearwardly relatively to the valve 4 until the end of the casing 1 engages the wider portion of the pillar 25. The casing 1 is urged forwardly into engagement with the socket 22 by means of a compression spring 26 surrounding the pillar 25 and engaging a collar 27 that is axially slidable upon the pillar 25.

The collar 27 provides a recessed seating 27A for receiving the end of the casing 1 and locating it relatively to the pillar 25. The sliding movement of the collar 27 under the force of the compression spring 26 is limited by means of an outwardly projecting shoulder 25B of the pillar 25, whereby the collar 27 is retained upon the pillar 25 when the cartridge case 1 is released therefrom.

The operation of the arrangement described above is as follows. When the air pressure within cylinder 21 is increased by the action of the pump, a force is exerted upon the casing 1 in the direction of the arrow X which is dependent upon the difference between the diameters of the spigot portion of the casing 1 and the end 5 of the valve member 4. This force is resisted by means of the compression spring 26 until it becomes sufficiently great to effect compression of the spring 26 so that the cartridge casing 1 moves towards the stepped shoulder of the pillar 25. The corresponding relative movement between the casing 1 and the valve 4 is effective to open the valve at the forward end of the casing 1 allowing air to enter.Upon release of the pressure within the cylinder 21, the casing 1 will return under the force of the compression spring 26 to close the valve and retain the pressure within the casing 1. Thus the assembly illustrated provides a non-return valve action, allowing pumping of the air chamber within the casing 1 to a high air pressure. It will be appreciated, however, that, in an advantageous manner, the maximum air pressure within the casing 1 is limited by the force of the compression spring 26.

It will be appreciated that various alterations may be made to the arrangement described above. For example, in the described arrangement the member 10 and the compression spring 11 were used simply as a convenient means of retaining the ring 9 in place. They could be replaced by any aiternative means, possibly fixed with respect to the portion 1A of the casing.

Another possible embodiment of the invention is shown Fig. 3, wherein similar reference numerals are utilised to indicate the same elements as shown in Fig. 1. In this arrangement the forward end 1 A of the casing includes both the forward spigot portion and the main body of the casing, and the portion 1B is a simple end plug threaded into the rear of the portion 1A. An 0-ring seal 30 may be provided to prevent leakage of air between the two parts of the casing 1. The valve member 4 is provided with a wider shoulder 40 intermediate the ends thereof, this shoulder forming a seating for a compression spring 35 which serves to bias the ring 9 forwardly towards the valve head 7.

The cartridge as shown in Fig. 3 may be charged and utilised in a similar manner as described above with reference to Figs. 1 and 2. However, charging of the cartridge could alternatively be effected without allowing relative movement of the valve member 4 and the casing 1, in which case the valve seat 9 can move rearwardly against the force of the compression spring 35, to act as a non-return valve. Moreover, the shoulder portion 40 of the valve member 4 and the internal wall of the casing 1 are arranged to cooperate with one another to throttle the flow of air from the chamber defined by the casing 1 towards the outlet orifice defined by the valve head 7 and the seating 9. Thus, upon initial opening of the valve by impact or pressure on the end portion 5, pressure drops will occur both across the valve head 7, and across the shoulder portion 40.Since the latter is of considerably greater area than either of the portions 5 and 7 of the valve, this will have the effect of generating an additional force driving the valve member 4 towards the open position.

In one particular example of the cartridge illustrated in Fig. 3, a cartridge having an internal volume of approximately 25 cubic centimetres was constructed utilising a valve member 7 having an overall length of approximately 47 millimetres the forward end 7 and the rearward end 5 both having a maximum external diameter of 5.2 millimetres. The internal diameter of the body of the casing 1 was 10.5 millimetres, the external diameter of the collar 40 was 10 millimetres and the latter was positioned 11 millimetres from the forward end of the valve member, so that the major volume of the cartridge casing was to the rear of the collar 40. The valve seat 9 was formed by cutting a section approximately 4.5 millimetres long from a portion of nitrile rubber tubing having an external diameter of approximately 7 millimetres and a wall thickness of approximately 1.25 millimetres.

It was found that when such a cartridge was charged to an internal air pressure of approximately 80 bar, the forces on the valve member and the ring 9 were such as to maintain an effective seal, whereas the cartridge could be discharged by means of an impact on the rear of the valve member by a firing mechanism providing a kinetic energy similar to that of a conventional firearm.

It was further found that in comparison with an identical cartridge in which the diameter of the shoulder 40 was reduced to that necessary only to support the spring 35, a substantially greater muzzle energy of the discharged pellet 3 was obtainable from a firing mechanism having the same kinetic energy. Thus, the presence of the wider shoulder 40, despite restricting the flow of air from the cartridge, appeared substantially to improve the efficiency of the cartridge by reducing the tendency of the valve member to close after the initial opening impact, as a result of the back pressure of air between the pellet 3 and the downstream side of the valve head 7.

Referring now to Fig. 4 of the drawings, there is illustrated a further embodiment of air cartridge in accordance with the invention, shown in association with diagrammatically il lustrated components of a gun adapted for firing the same.

Unlike the cartridge of Figs. 1 to 3, the cartridge of Fig. 4 does not simulate the construction of a centre-fire cartridge of a firearm, but is intended for use in a specially adapted air gun. This enables the construction of cartridge to be simplified, although it will be appreciated by one skilled in the art that the same principle could be applied to the construction of a simulated centre-fire cartridge of the kind described in the above-mentioned German Patent Specification No. 119323, or United Kingdom Patent Specifications Nos.

1601917 and 1601918.

The cartridge comprises an outer casing 100 formed, for example, of brass, and defines a cylindrical internal bore 101 containing a valve member 102, the latter being retained within the casing 101 by means of a threaded end plug 103 screwed into the rear end of the casing 100.

The valve member 102 is constructed of a suitable synthetic plastics material, such as a polyamide and preferably nylatron. A forward end 102A of the valve member 102 is in the form of a disc-shaped valve head which engages a conical valve seat 105 formed on the casing 100. The cone angles of the valve seat 105 and the valve head 102A are such that the valve head 1 02A is centred by the valve seat when closed under thrust as described below. The cone angle of the valve head 102A is preferably greater than that of the valve seat 105 to ensure that sealing commences at the outer diameter of the valve head for the reason described below. A cone angle of approximatelyl25" for the valve seat and 135 for the valve head has proved suitable.The rear end of the valve member 102 comprises a cylindrical portion 106, the diameter of which corresponds to that of a bore 107 in the end plug 103, so that the valve member 102 is free to slide longitudinally within the casing 100, with the portion 106 received within the bore 107.

An 0-ring 108 is arranged between the internal surface of the bore 100, and the external surface of the portion 106 of the valve member 102, in order to provide a gas tight seal between the bore 101 and the valve member 102, thus also providing a gas tight seal between the casing 100 and the end plug 103. A radially extending flange 109 adjacent the portion 106 of the valve member 102 serves to limit rearward movement of the latter. The two portions 102A and 106 of the valve member 102 are interconnected by a stem portion 110 that is of a diameter sufficient to resist the tensile stresses on the body of the valve member 102, as will be described below.

The bore 104 at the forward end of the casing 100 receives therein as a sliding fit the stem the stem portion 111 of an apertured headed plug having a bore 112 matching the calibre of a barrel 113 of an air gun in which the cartridge is to be fired. A flange 114 at the forward end of this plug has a radially extending front surface that makes abutment with a corresponding surface at the forward end of the chamber of the gun, and thus provides a seal between the forward end of the cartridge and the barrel 113.

The rear end of the cartridge casing 100, together with the plug 103, extends a short distance from the chamber of the gun. The casing 100 is a loose sliding fit within the chamber and is held therein by a firing member 116 which is in the form of a lever pivoted about a pin 117 fixed with respect to the barrel 113 in the frame of the airgun, not shown. The lower end of the lever 116 is in the form of a stirrup 11 6A and carries a pin 140 about which is pivoted the upper end of a trigger member 141 located between the two limbs of the stirrup 116A. The trigger member 141 is also linked to a fixed pivot 142 located in the frame of the airgun by means of a pair of links 143 mounted on the pivot 142 and pivoted on a pin 144 passing through the trigger member 141.A torsion spring 145 is located around the pivot 142 and engaged between the airgun frame and the links 143 to lightly spring load the latter in the clockwise direction.

Actuation of the airgun illustrated is as follows. The interior space within the cartridge casing 100 may be charged to a high air pressure, as described below, as a result of which the valve member 102 is subjected to a forwardly directed force due to the fact that the external diameter of the end portion 106 is smaller than the outer diameter of the valve head 102A.

After the cartridge has been charged to high pressure, a pellet 118 to be fired by the gun is inserted into the bore 112 of the front end plug, prior to insertion of the latter into the frontal bore 104 of the cartridge 100.

It will be noted that the axial length of the stem portion 111 of the front plug is greater than the distance between the forward end of the cartridge casing 100 and the forward end of the valve member 102, so that when the frontal plug is forced towards the interior of the cartridge, the head 102A of the valve member 102 can be displaced from the valve seating 105. This displacement is effected by applying rearward manual pressure to the lower end of the trigger member 141. It will be noted that the lever 116, the trigger member 141 and the links 143 form a trapezium linkage of which the pivots 117 and 142 are fixed and pins 140 and 144 are movable.The trigger member 141 and the links 143 thus form a toggle linkage which is forced towards an over-centre position by rearward pressure on the trigger and can thus transmit force tending to pivot the firing member 116 in the anti-clockwise direction in Fig. 4 with a substantial mechanical advantage. The lower edge of the plug 103 is correspondingly urged forwards to move the casing 100 within the chamber of the airgun, the member 116 being shaped to leave a slight clearance at the upper edge of the plug 103 so that the minimum effective length of the lever arm of the firing member 116 is used.

The diameter of the internal bore 104 of the casing 100 is smaller than the external diameter of the rear portion 106 of the valve member 102, and therefore as soon as the seal between the valve seat 105 and the valve head 102A is broken, the increased air pressure on the forward side of the valve head 102A causes a rearward thrust upon the valve member 102, so that this is caused to move rearwardly very rapidly, freeing the bore 112 within the forward end plug, so that compressed air from the cartridge can pass through the latter and drive the pellet 118 through the barrel 113.The rear portion 106 of the valve member now engages the firing member 116 so that its rearward movement is arrested and the air pressure within the cartridge casing 100 causes a reaction whereby the latter is driven forwardly to maintain a tight seal between the front face of the flange 114 of the end plug and the forward end of the chamber of the airgun. At this point the toggle linkage has preferable moved just overcentre until the trigger member 141 has engaged an end stop, so that the reactive forces are not transmitted to the trigger finger of the user.

It will be appreciated that the trigger pressure required to fire the airgun will be a function of the mechanical advantage of the toggle lever linkage and the force closing the valve head 102A. The latter will in turn depend upon the internal gas pressure of the cartridge and the difference between the diameters of the portion 106 and the head 102A of the valve 102. In practice a compromise between effective sealing of the cartridge, cartridge power, and an acceptably low trigger pressure can however, be achieved.

Unloading of a fired cartridge is illustrated in Fig. 5. By forward and upward pressure on the rear of the trigger member 141 the toggle lever linkage can be pivoted in a direction such that the links 143 pivot anticlockwise against the loading of torsion spring 145 and the firing member 116 moves clockwise to free the end of the chamber of the gun. The toggle formed by the trigger member 141 and the stirrup 11 6A moves overcentre just before the firing member 116 meets and end stop 146, and thus the firing member 116 is latched in the open position. To return the firing member 116 to the closed position the back of the trigger member 141 is pushed forwards and downwards, the torsion spring 145 then serving to urge the firing member 116 lightly towards the closed position.

Referring now to Fig. 6, the cartridge of Fig.

4 is shown in place in a pump by means of which it may be charged with a high air pressure.The pump comprises a spigot 120 that is dimensioned as a sliding fit within the frontal bore 104 of the cartridge and carries an 0ring 121 providing an airtight seal. The spigot has a capillary bore 122 communicating between the end of the spigot 120 and a pressure chamber 122, only part of which is shown in the drawing. This pressure chamber may, for example, comprise a cylinder containing the sliding piston of an air pump not shown, in a similar manner to that of Fig. 3.

Secured to the body of the air chamber 122 in any suitable manner is a cylindrical external housing 124, the interior of which is open to atmosphere. An annular washer 125 is arranged as a sliding fit around the periphery of the spigot 120, and is retained in place thereon by means of a shoulder 126 formed internally on the housing 124. The washer 125 is spring urged to the right as viewed in the drawing by means of a compression spring 127 surrounding the spigot 120 and engaging between the washer 125 and the end wall of the pressure chamber 123. Movement of the washer 125 against the force of the spring 127 is limited by a step 120A on the spigot 120. The free end of the cylindrical housing 124 receives a stepped end plug 128 that is screw threaded therein at 129.A reduced diameter portion 130 of the end plug 128 is arranged to penetrate the bore 107 at the rear of the cartridge in order to engage the rear portion 106 of the valve member 102 and thrust the valve member forward so that the valve head 102A makes tight engagement with the valve seat 105. The forward end of the cartridge is thus urged against the washer 125 which can yield under the loading by the compression spring 127 until it engages the step 120A.

Initially the plug 128 is unscrewed slightly to enable insertion of the cartridge casing 100 through a lateral aperture, not shown, in the housing 124, and after engaging the cartridge casing with the spigot 120 the plug 128 is screwed into the housing 124 to engage portion 106 and compress the spring 127 until the washer 125 is just short of the step 120A.

When air under high pressure is pumped through the spigot 120, an air pressure initially builds up within the bore 104 of the cartridge casing on the upstream side of the valve head 102A. Since the effective internal diameter of the valve head 102A is greater than that of the bore 104, this causes an axial thrust to be applied to the casing 100 in accordance with the difference in diameters of the bore 104 and seal at the valve seat 105.

Thus the casing 100 is caused to move axially further compressing the spring 127 so that the valve head 102A of the valve member 102 is released from the seating 105, and the pressurised air can flow into the interior of the casing 100.

As air flows into the casing 100 the pressure difference across the valve seat 105 will fall. Assuming an intermittent supply of air from the pump, as in the case of a reciprocating piston pump, the axial thrust on the casing 100 will correspondingly fall, allowing the compression spring 127 to relax, so that the valve head 1 02A re-engages the seating 105 to retain air within the casing. The action of the spring 127 thus provides a non-return valve action retaining compressed air within the cartridge casing.

It will further be noted that as the pressure applied to the cartridge casing via the spigot 120 increases, in addition to the above-mentioned axial thrust tending to open the valve, there will be an additional thrust developed on the cartridge casing when the valve is open and there is no pressure drop across the seat 105, as a result of the fact that the diameter of the bore 104 is smaller than the external diameter of the portion 106 of the valve member. The compression spring 127 is selected to have a force sufficient to overcome any such axial thrust at pressures below the maximum pressure to which the cartridge is to be charged.However, when the internal pressure is such that the axial thrust upon the casing 100 overcomes the force of the spring 127, it will be appreciated that the valve head 102A will no longer exert a non-return valve action upon the seating 105, and the valve will not close to retain pressure within the casing until the internal air pressure within the cartridge is reduced to the point at which the spring 127 can relax to close the valve.

Thus it will be seen that the system has an inherent pressure limiting function, preventing over-charging of the cartridge and also enabling a series of cartridges to be charged consistently all to the same pressure. It is preferable that the movement of the washer 125 is limited by the step 120A to that which is essential for opening of the valve head 102A, in order that hysteresis in the opening and closing actions of the valve caused by friction resulting from 0-rings 121 and 108 is reduced to the minimum.

Conveniently, the axially displaceable washer 125 may be coupled with means, not shown, for providing an indication when the pressure limit has been reached. For example, the step 120A may be more electrically insulating and contain contacts coupled to the circuit of an indicating device such as a light emitting diode, which contacts become bridged by contact with the washer 125. Such an indication may be useful in the case where the air pump is a manually actuatable pump. It is also feasi ble that an electrically driven compressor or electrically actuatable solenoid valve of a power actuated cartridge-charging apparatus may be controlled in accordance with the output signal of such an indicating circuit.

From the above description it will be seen that there is provided a novel and extremely simple fireable air cartridge for use in an air gun. In the embodiment of Fig. 4, the cartridge casing comprises only two simply constructed components, in addition to an end plug for containing the pellet, a valve member that can be produced by injection moulding from synthetic plastics material, and a standard 0-ring. Moreover the cartridge can be charged via a simply constructed pump which provides an inherent pressure-limiting function and can readily be rendered tamper-proof to prevent deliberate over-charging of the cartridges to an extent that would be dangerous or unlawful.

It will be appreciated that various alterations and modifications may be made to the arrangements described above without departing from the scope of the invention. For example, the stem 110 of the valve member may have a portion of reduced diameter to cause breakage of the valve member under tension applied thereto in the event of charging of the cartridge to excess pressures, thereby disabling the cartridge and rendering it unusable.

Also, although the valve has been described as being fireable by axial movement of the valve member 102 as a whole, it is feasible that with an appropriate elastic modulus of the valve stem 110, the latter may be caused to stretch under the applied tension when the cartridge is in the charged condition, so that the portion 106 of the valve member reaches its rearward end position whilst the forward portion of the valve member maintains a seal.

Provided that the elasticity of the material forming the valve member is such that it is restored to its original length upon release of pressure from the cartridge, the cartridge may still be fired in much the same manner as described above, with the exception that rapid movement of the rear portion 106 of the cartridge is avoided during firing, so that the 0ring 108 is required to function only as a static seal, and its working life is correspondingly extended. Alternatively the substantial rearward force that is exerted by rearward movement of the valve member 102 may be utilised by causing the rearwardly moving portion 106 to engage an inertia member of an airgun mechanism that is arranged to provide a selfloading function equivalent to that of a recoilactuated semi-automatic firearm. If necessary the force developed to power such a recoil action could be increased by the modification shown in Fig. 7. In this embodiment a rearward portion 150 of the front end plug is of reduced diameter and arranged to engage in a recess in the front of the valve head 102A.

Discharge of air from the cartridge can thus be delayed until the valve member 102 has transferred sufficient energy to a recoiling inertia member that can store the kinetic energy required to cycle the self-loading action of the weapon. Such a weapon would preferably use a firing member to discharge the cartridge by impact rather than by pressure as in the case of member 116.

In another arrangement the spring 127 of the pump of Fig. 6 may be omitted if the dimensions of the cartridge are changed so that the diameter of the bore 104 is very slightly larger than that of the portion 106 of the valve member. The cartridge will then be inherently self closing under the applied pressure from the pump. Provided that the internal diameter of the valve seal is sufficiently greater than that of the bore 104 the valve will still have an effective non-return action although without the pressure limiting function provided by the spring 127.

Claims

1. A cartridge of the kind adapted to be charged with compressed gas and discharged in a small arm by an appropriate firing mechanism to propel a missile, comprising a cartridge casing defining a gas receiving space and having apertures at respective ends of the space, and a valve member arranged to extend within said casing to seal said apertures simultaneously and retain compressed gas within said space, the arrangement being such that in the charged state of said cartridge the valve member is biased axially into a sealing position but the valve member and the casing are capable of being relatively axially displaced by a thrust force to open one aperture for the discharge of gas to propel said missile whilst the valve member maintains a seal at the other aperture, wherein the said one aperture is provided with a valve seat against which a valve head of the valve member can form a seal, and the effective cross section of the valve seat and the cross section of the seal at the other aperture are such that when the said space is charged to an elevated gas pressure unequal forces are developed on the corresponding closing portions of the valve member and the resultant of said forces provides or assists the said biasing of the valve member to maintain a seal between the said valve head and said valve seat.

2. A cartridge as claimed in claim 1, wherein said valve head is located on the downstream side of said valve seat with reference to the direction of discharge of air from the cartridge, at a front end of the cartridge, and said valve member comprises a stem portion extending through the said other aperture and accessible at the rear of the cartridge to receive thrust or impact from a firing mechanism for forward displacement of the valve head from the valve seat.

3. A cartridge as claimed in claim 2, wherein the said valve seat is provided by an elastic ring supported within said cartridge casing such that the internal diameter of the ring is smaller than the outer diameter of the valve head, the ring being capable of passing over the valve had when in the free state but, when confined by the said casing, being capable of arresting the valve head against the said biasing force.

4. A cartridge as claimed in claim 3, wherein the said ring is restrained within the casing against axial forward movement by a radially inwardly projecting lip surrounding the valve head but is axially rearwardly movable against biasing means to form, with said valve member, a non return valve enabling charging of the cartridge with compressed gas through said one aperture.

5. A cartridge as claimed in any one of claims 2 to 4, wherein said valve member carries a baffle defining between itself and the internal wall of the said casing a restricted passage for the flow of gas from the said space to said one aperture, the effective area of said baffle being sufficiently greater than that of the said other aperture and the baffle being so located that upon opening of said one aperture with the cartridge in the charged condition the pressure drop across the baffle due to the flow of gas through said one aperture is effective to urge the valve towards the open position.

6. A cartridge as claimed in claim 1, wherein the said valve head is located on the upstream side of said valve seat with reference to the direction of discharge of air from the cartridge, at a front end of the cartridge, and said cartridge includes a member adapted to extend through the said one aperture and providing an abutment accessible at the front of the cartridge to receive thrust or impact for rearward displacement of the valve head from the valve seat.

7. A cartridge as claimed in claim 6, in combination with a gun having a firing mechanism therefor, wherein the cartridge casing is arranged to be received by a chamber of the gun in such a manner that it is forwardly displaceable relatively to the barrel of the gun by thrust from the firing mechanism, said chamber having an abutment for engagement by the corresponding abutment of the cartridge, whereby said forward displacement of the cartridge casing causes corresponding rearward movement of said valve head from the valve seat.

8. A cartridge or combination as claimed in claim 6 or 7, wherein said member providing said abutment comprises a hollow sleeve slideable within said one aperture and arranged to receive a said missile and said abutment is adapted to make a face seal with a corresponding abutment surface of a or the chamber of an or the airgun.

9. A cartridge or combination as claimed in any one of claims 6 to 8, wherein the said valve seat is formed integrally with the valve casing and the valve member is formed of synthetic plastics material which is deformable by engagement with said valve seat to form an airtight seal.

10. A cartridge or combination as claimed in claim 9, wherein the said valve seat has a conical surface and the valve head has a conical surface with a slightly shallower angle than that of the valve seat, whereby the valve seal occurs, or is initiated, at the outer rim of the valve head.

11. A cartridge or combination as claimed in any one of claims 6 to 10, wherein said abutment member and said valve are arranged to interengage over an axial distance, whereby the opening in said abutment member is obstructed during initial rearward movement of the valve member when the cartridge is fired.

12. For use with a cartridge as claimed in any one of claims 1 to 11, a charging device comprising a union coupled to a source of compressed gas and adapted for gas tight sliding engagement with said cartridge at the end having said one aperture and means arranged to be fixed with respect to said union and to engage the said valve member through said other aperture, the arrangement being such that during charging of the cartridge from said union, the casing of the cartridge is free to move relatively thereto to provide a non return valve action.

13. A charging device as claimed in claim 12, for use with a valve the dimensions of which are such that when said space is coupled to said union and at an elevated gas pressure the cartridge casing is urged in a direction opening said valve, said device including means for biasing said casing towards the valve closed position at charged gas pressures below a predetermined limit.

14. For use with a cartridge as claimed in any one of claims 6 to 11, a gun comprising a chamber arranged to receive the cartridge casing as a sliding fit and having a forward abutment surface surrounding the bore of the barrel, and a firing mechanism including a pressure lever pivotable into engagement with the rear of the cartridge casing, said lever being coupled to a toggle linkage, including a trigger member whereby pressure on the trigger is transmitted as forward thrust on the rear of the cartridge at a mechanical advantage obtained in the region of the overcentre position of the toggle.

15. A gun as claimed in claim 14, wherein said lever and said toggle linkage form a trapezium linkage allowing rearward pivoting of the pressure lever to free said chamber for loading of the cartridge therein, upon forward pressure on the rear of the trigger member.

16. A firable compressed gas cartridge substantially as described herein with reference to Figs. 1 to 3 of the accompanying drawings.

17. The combination of a cartridge and compressed gas charging device substantially as described herein with reference to Fig. 6 of the accompanying drawings.

17. A firable compressed gas cartridge substantially as described herein with reference to Fig. 4 or 7 of the accompanying drawings.

18. An airgun substantially as described herein with reference to Figs. 4 and 5 of the accompanying drawings.

19. A compressed gas charging device substantially as described herein with reference to Fig. 2 of the accompanying drawings.

20. A compressed gas charging device substantially as described herein with reference to Fig. 6 of the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1, 12 to 15, 18, 19 and 20 above have been deleted or textually amended.

Claims 16 and 17 above have been re-numbered as 14 and 15 and their appendancies corrected.

1. A cartridge of the kind adapted to be charged with compressed gas and discharged in a small arm by an appropriate firing mechanism to propel a missile, comprising a cartridge casing defining a gas receiving space and having apertures at respective ends of the space, and a valve member arranged to extend within said casing to seal said apertures simultaneously and retain compressed gas within said space, the arrangement being such that in the charged state of said cartridge the valve member is biased axially into a sealing position but the valve member and the casing are capable of being relatively axially displaced by a thrust force to open one aperture for the discharge of gas to propel said missile whilst the valve member maintains a seal at the other aperture, wherein the said one aperture is provided with a valve seat against which a valve head of the valve member can form a seal, and the effective cross section of the valve seat and the cross section of the seal at the other aperture are such that when the said space is charged to an elevated gas pressure unequal forces are developed on the corresponding closing portions of the valve member and the resultant of said forces acts in a direction tending to urge the valve member towards said valve seat.

12. In combination with a cartridge as claimed in any one of claims 1 to 11, a charging device comprising an outlet coupled to a source of compressed gas and adapted for coupling with said one aperture of the cartridge and means arranged to engage the said valve member through said other aperture, the arrangement being such that during charging of the cartridge from said outlet, the valve member is arrested by said engagement means while the casing of the cartridge is free to move relatively thereto to provide a non return valve action.

13. A combination as claimed in claim 12, wherein the dimensions of the valve are such that when said space is coupled to said outlet and at an elevated gas pressure the cartridge casing is urged in a direction opening said valve, said device including means for biasing said casing towards the valve closed position at charged gas pressures below a predetermined limit.

16. The combination of a cartridge and compressed gas charging device substantially as described herein with reference to Fig. 2 of the accompanying drawings.