GB2149483A - Air weapons - Google Patents

Abstract

A recoilless air rifle has a compression system which comprises a pair of horizontally opposed gas spring powered pistons 16, 18 which on firing, accelerate towards one another under the influence of gas expanding within the gas springs, to compress a charge of air within a compression chamber 32 and fire a pellet 37 from the rifle barrel 38, the gas pressure force on each piston being balanced by means of a pipe 31 which interconnects the gas expansion chambers 28, 30 of the gas springs. The pistons 16, 18 are linked by a rack and pinion device 44, 46, and a cocking lever 48 is connected to the pinion 46. A trigger mechanism 50 includes a sear 50A which engages a recess 52 in the rear end of the rear piston 18. <IMAGE>

Description

SPECIFICATION Improved air weapons This invention relates to air weapons, and particularly but not exclusively, to air rifles.

The three basic types of air rifle may be classified according to their respective firing mechanisms, namely the pump type, the gas operated type and the spring type. The present invention concerns a development of the spring type of air rifle.

In many examples of this type of air rifle, a steel cylinder (normally about three centimetres by thirtyfive centimetres long) is the basis of the firing mechanism. The barrel is hinged to the front of the cylinder to enable the breech to be opened and when the breech is opened, a cocking mechanism acts on a solid piston slidable within the cylinder to drive the piston rearwardly and compress a coiltype firing spring. The firing mechanism is latched by a trigger mechanism in the rearward position in which the firing spring is fully compressed. With a pellet inserted in the breech and the latter closed the gun is ready to fire. A pull on the trigger releases the latched firing mechanism so that the piston is driven forwardly at high speed under the action of the firing spring.The air in the cylinder in front of the piston is increasingly compressed to exceed a threshold at which the pellet is ejected through the barrel at high speed.

The average marksman, for example using an air rifle of this type both for target shooting and for shooting live quarry such as rabbits, vermin and birds such as pigeons, will quite easily use between 4,000 and 6,000 pellets in one year. During such a period of shooting, assuming that it is a new gun, there will be an initial "tuning-up" period at which time adjustments to the sights, often of a telescopic nature (and commonly called "zeroing the scope") will involve the use of up to say 500 pellets. During this time the owner of the gun will also make an assessment of the type of pellet he wishes to use, and this in itself can necessitate variations in calibrations of the sights, since the weight and design of pellet from one make to another can affect the pellet velocity.On the assumption that the gun, and therefore its coiled-compression spring are new, this initial "tuning period" can have severai effects. Firstly, the other moving parts of the gun can begin to get "bedded-in" e.g. the piston seals can free-up slightly which will tend to increase pellet velocity. This, in the initial period of use of the new gun, tends to be balanced by the loss of power which always occurs with the mechanical or coil spring even over the first 500 to 1,000 shots. A gun which is designed, for example, to produce an energy level at the muzzle of just below 12 ft Ibs (the maximum limit for unlicensed air guns in the U.K.) may already suffer a drop in performance perhaps of the order of 5 to 10% of the peak energy.

Continued use of the gun, after this initial period does not tend to produce such a rapid deterioration in performance, but there tends to be a further gradual but steady deterioration in spring performance.

The springs of these guns are generally manufactured from high quality round steel wire, which has previously been hardened and tempered and after winding the spring is stressed-relieved at low temperatures for several hours before testing.

When this type of coil spring is compressed, the energy is in fact stored by the wire of the spring twisting but it is well known that repeated compression and release of this type of spring several thousand times results in a loss of spring performance, primarily due to a reduction in spring length, for example due to deterioration of either the whole of the spring, the result of which the pitch of the coils change, or perhaps a localised collapse of a few coils.

From the point of view of the user of the gun, this deterioration is gradual, and whilst it can to some extent be countered by resetting the sights, and this may be adequate for short range stationary target shooting even where the loss of efficiency is considerable, serious loss of power due to spring shortening seriously affects the use of a rifle when employed for live quarry shooting where the target distance may be considerably greater.

As a result of these well recognised problems with a coil spring, a keen marksman will re-spring his gun, i.e. replace his spring, for example at the beginning of a shooting season, and marksmen who use a very large number of shots will perhaps regularly re-spring their guns at three monthly intervals which is naturally a costly and time consuming task to say nothing of the gradual loss of power even during those three months periods.

It is also well known that owners of this type of gun, when used for shooting live quarry, desirably would like to maintain the gun cocked and ready for instant use, but this can mean a long cocked period of up to say haif an hour or more which, if regularly carried out, tends prematurely to affect the coil spring efficiency. As a consequence the gun user tends to release the main coil spring of the gun and not have it readily cocked as often as he would desire when shooting live quarry. There has thus clearly been a demonstrable need for a gun which can be left cocked indefinitely without loss of spring efficiency.

Another problem which is not uncommon is that spring breakage can occur, for example due to incorrect tempering of the high tensile wire used for producing the springs.

These now well recognised problems with compression coil spring air guns have clearly indicated a long felt need for a more constant and long-lived power source. The inventors therefore developed a gas operated rifle which is the subject of British Patent Specification No. 2084704 and corresponding Patent Applications in other countries. This type of rifle is now marketed in significant numbers by the Applicants and has proved, in the field, to be greatly superior to its predecessors. This successful rifle basically provides a single gas spring for producing an air pressure to fire the pellet.

The earlier rifle of the applicants therefore, incorporates the concept of replacing the conventional coil-type compression spring with a gas spring and this enables various advantages, including a smooth and consistent performance, to be achieved. The rapid forward movement of a single hollow piston during the firing process of this rifle does, however, produce a substantial rearward reaction, or recoil, which although not unusual in the air rifle field, is a substantial source of potential inaccuracy.

British Patent Specification No. 803028 (GISS) aims to deal with the adverse effects of recoil, and discloses a method of operating two coil spring driven pistons in horizontal opposition to one another.

The pistons are mechanically linked by a rack and pinion mechanism which ensures that they accelerate towards one another at the same rate. It is intended that pistons should be of equal mass so that the inertia forces due to movement and stopping of each piston are substantially equal; hence these forces, which are in opposite directions, cancel one another out. Unfortunately due to the practical impossibilities of achieving a force balance between the two coil springs either because of manufacturing limitations, or because the spring force of the coil springs deteriorate at different rates, one coil spring will always tend to provide some of the driving force for the opposing piston through the rack and pinion mechanism. The consequent transmission of driving force at high velocity through the rack and pinion mechanism can lead to wear and eventual failure of the mechanism.

The object of this invention is to overcome the disadvantages of the above mentioned air weapons and incorporate all the advantages of a gas spring operated weapon in a reliable, substantially recoilless form. A further object of the invention is to provide a mechanically simple, easy to assemble, repair and service, substantially recoilless air weapon.

According to one aspect of the present invention an improved airweapon air compression system comprises a plurality of pistons arranged in a substantially recoilless manner to compress air in a compression chamber for the firing of a pellet from an air weapon, each of the pistons being integral with or connected to a movable element of a different gas spring, each of the gas springs including an expansion chamger arranged to contain a charge of compressed gas and each of the expansion chambers being connected or connectable to at least one other thereby to balance the pressures in the connected expansion chambers at all times.

Preferably each piston is arranged, on firing, to compress air in the compression chamber.

According to another aspect of the present invention an improved air weapon air compression system comprises a plurality of pistons for compressing air in a compression chamberforthe firing of a pellet from an air weapon, each of the pistons being integral with or connected to a movable element of a different gas spring, each of the gas springs including an expansion chamber arranged to contain a charge of compressed gas and each of the expansion chambers, being connected or connectable to at least one other thereby to balance the pressures in the connected expansion chambers at all times, the pistons and gas springs being arranged in such a configuration that the resultant of the forces due to the movement of each piston and movable element is substantially zero.

In accordance with yet another aspect of the present invention a substantially recoilless air weapon in which a pellet is expelled from a barrel by air compressed within a compression chamber includes a plurality of gas springs each providing a movable piston which has a piston crown that faces, and partially defines, the compression chamber, each gas spring having an expansion chamber partially defined by its respective movable piston, the expansion chambers being capable of being filled with a charge of compressed gas, and cocking means arranged to move the pistons in directions which increase the volume of compression chamber and simultaneously further compress the gas in each expansion chamber, a gas duct being included to place each of the expansion chambers of the gas springs in communication with at least one other expansion chamber so that the forces due to the movement of connected gas springs may be substantially equal.

Preferably the substantially recoilless air weapon includes a single charging point for the introduction of the charge of compressed gas into the interconnected expansion chambers.

More specifically the movable pistons of the substantially recoilless air weapon are mechanically linked by coupling means and the cocking means is arranged simultaneously to move the pistons via the coupling means.

According to a further aspect of the invention an improved air weapon includes a barrel having an inner end into which a pellet can be loaded, an outer main cylinder including a compression chamber having an output port communicating between the compression chamber and the inner end of the barrel, the outer main cylinder having a bore containing a pair of gas springs each of which has a stationary hollow part positioned within a section of the bore of the outer main cylinder and providing an annulus between said bore and said hollow part, each gas spring also including a movable piston which is in the form of a forward hollow part which is mounted partially in the respective annulus for reciprocal movement with respect to the respective stationary hollow part, with the two hollow parts of one gas spring forming a first expansion chamber and the two hollow parts of the other gas spring forming a second expansion chamber, the movable pistons having opposed crowns which partly define the compression chamber, first sealing means being provided between the crown of each piston and the bore of the outer main cylinder, and second sealing means being provided in each gas spring between its respective hollow parts for containing a permanent charge of compressed gas in the two expansion chambers, a duct being provided permanently to place the two expansion chambers in communication with one another thereby to equalise the pressures acting on the two pistons, cocking means being provided, for moving the pistons simultaneously away from one another to reduce the expansion chamber volumes and increase the compression chamber volume, and trigger means being provided for releasing the pistons simultaneously to compress the air within the compression chamber to expel the pellet.

The invention may be carried into practice in various ways, but one specific em bodiment will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectionalised side elevation of an air rifle air compression system in the loaded position; Figure 1A shows the cocking mechanism return spring; Figure 1 B is an enlarged sectionalised side elevation of the breech; Figure 2 is a scrap sectionalised underside plan of the air rifle air compression system shown in figure 1 in which parts of the cocking mechanism have been omitted to show the rack and pinion in the cocked position; Figure 3 is a simiiar view to figure 1 showing the system in the fired position; Figure 4 is a similar view to figure 2 showing the rack and pinion in the fired position; and Figure 5 is an enlarged view of the balance pipe coupling.

The illustrated air rifle comprises a barrel 38 having a bore 38A, which may be rifled if necessary, the right hand or inner end of the bore 38A terminating at a breech 36 in which a pellet 37 is shown which can be introduced into the breech by a conventional bolt 55. In other arrangements the breech may be loaded by a conventional break action in which the barrel is pivoted with respect to the remainder of the rifle.

In the embodiment shown, the barrel is supported by a barrel support 56 which, in turn, forms part of a stock of the rifle, only certain parts of which are illustrated for the purpose of describing the present invention. Mounted below the barrel, breech and bolt is a main, outer cylinder 10 which as will be described, with other parts, forms the compression system of the rifle containing a pair of gas springs which are mounted for operation in opposition to one another. Thus the cylinder 10 includes, within its bore, a pair of opposed hollow pistons 16 and 18 which, for convenience, will be referred to as the forward piston 16 and the rearward piston 18. Each piston is sealed during the course of its sliding movement within the bore 10 by an appropriate 0ring seal 17 mounted in a groove 17A formed in the respective crown of the piston.Between the crowns 16A and 18A, the outer cylinder 10 forms an air compression chamber 32. Midway along the length of the air compression chamber 32 a radially outwardly extending port 34 provides communication between the chamber 32 and the breech, just behind the pellet 37 so that, on firing the rifle, as will be described, the pistons 16 and 18 move at high speed towards one another, compressing air to a high pressure within the chamber 32, and at a given threshold value of the air pressure at the breech, the pellet 37 will be expelled down the barrel bore 38A.

The manner in which each of the hollow pistons 16 and 18 partly form a pair of gas springs will now be described.

Stationarily mounted within the opposite ends of the outer cylinder 10 are inner cylinders 12 and 14, the inner cylinder 12 being closed at its forward end 20 and the other inner cylinder 14 being closed at its rear end by a tail piece 22 which contains a valved gas charging passage 24 which is sealed by a grub screw. Thus a valve 58 is provided by which gas under high pressure can be fed into the interior of the inner cylinder 14 and, as will be described, also transmitted to the inner cylinder 12 to fill the gas spring at that end of the outer cylinder 10.

The opposed ends of the inner cylinders 12 and 14 are received telescopically within the respective boresofthe pistons 16 and 18. Positioned around the opposed ends of the inner cylinders 12 and 14 area pair of seals comprising an O-ring seal 26 and a lip seal 27. The lip seals 27 are located in grooves in the protruding ends of short tubes 29, the inner ends of which are secured by Loctite adhesive in the opposed open ends of the inner cylinders 12 and 14.

Each lip seal is undercut on it's face which opens towards the interior of the respective pistons 16 and 18 so that, when a charge of compressed gas is introduced into the combined spaces within the respective inner cylinders and pistons, such pressure biases the peripheral lip of the seal against the inner bore of the respective piston. In this way, sealed expansion gas chambers 28 and 30 are provided forming the two gas springs mounted within the outer cylinder 10.

Figure 1 shows the pistons 16 and 18 in a retracted or cocked condition with the air compression chamber 32 at maximum volume. It will be appreciated that the inner cylinders 12 and 14, in their external regions which are telescopically arranged with respect to the pistons, are reduced to provide in each case an annulus between the respective inner cylinders an outer cylinder 10 walls within which the respective open ends of the pistons 16 and 18 can be received fully in the cocked condition of figure 1.

To achieve cocking, each piston has a radially outwardly extending dog 31 and these dogs are connected to floating shoes 42 which in turn are mounted on respective racks 44 which together cooperate, at their ends remote from the shoes 42, with a centrally disposed pinion 46. The pinion 46 is mounted on a bearing which can be secured either to the external surface of the outer cylinder 10, or to another part of the stock of the gun.

In order to allow for longitudinal movement of the racks and the dogs 21, the wall of the outer cylinder 10 is provided with an appropriate longitudinal slot 21A. The length of these slots 21A does not, of course, extend beyond the respective crowns of the two pistons in their retracted or cocked condition, so that the integrity of the air compression chamber 32 is not affected.

The effect of the rack and pinion arrangement is such that the pistons 16 and 18 are displaced with equal and opposite movements and cocking is achieved by means of a cocking lever 48 and a trigger mechanism 50 which includes a sear 50A which passes through a slot 50B in outer cylinder 10 and engages in a recess 52 in the external rear end of the rear piston 18 to retain that piston in its cocked position, the other, forward, piston 16 also being maintained in its cocked position by virtue of the rack and pinion mechanism.

The movement of the pistons 16 and 18 away from one anotherto the figure 1 position will cause further compression of the already compressed gas in the gas chambers 28 and 30, and the rifle is therefore cocked ready for firing, assuming the pellet 37 has been loaded into the breech.

According to the present invention, the interiors of the inner cylinders 12 and 14 are directly interconnected by a balance pipe 31 shown in Figure 2, thereby to place in balanced communication with one another the gas chambers 28 and 30. Figure 5 illustrates the manner in which each end of the balance pipe 31 communicates through the wall of the outer cylinder 10 by way of a radial pipe 31A which is sealed with respect to a mounting post 31 B.

When the trigger is operated, as mentioned above, to release the rear piston 18, by virtue of the balancing pipe 31 and the equal pressures in the gas chambers 28 and 30, the two pistons 16 and 18 are propelled towards one another at the same speed to cause high compression of the air in the air compression chamber 32, this being communicated to the breech via the port 34 to propel the pellet 37 down the barrel at high speed.

The part 34 being sealed from the atmosphere by the forward and rearward barrel mounting O-ring seals 53 and 54 respectively, and the rear end of the barrel being sealed by the bolt 55 and the bolt O-ring seal 57. It is to be noted that, with this arrangement, although there is a mechanical connection between the two pistons 16 and 18 via the rack and pinion mechanism, the rack and pinion mechanism does not have to transmit any force between the two pistons during firing, since the pressures in the gas chambers 28 and 30 are balanced. In this way, although the rack and pinion mechanism will also operate at high speed, it is not under load and therefore does not tend to be worn to any degree.

It should be appreciated that although an equal sized and massed piston arrangement has been disclosed, the invention is applicable to any force balanced pistons. Therefore a smaller, lighter, faster piston acting in opposition to a larger heavier slower piston could achieve the same effect.

Claims (9)

1. An airweapon air compression system comprising a plurality of pistons arranged in a substantially recoilless manner to compress air in a compression chamber for the firing of a pellet from an air weapon, each of the pistons being integral with or connected to a movable element of a different gas spring, each of the gas springs including an expansion chamber arranged to contain a charge of compressed gas and each of the expansion chambers being connected or connectable to at least one other thereby to balance the pressures in the connected expansion chambers at all times.

2. An air weapon compression system as claimed in claim 1 where each piston is arranged, on firing, to compress air in the compression chamber.

3. An air weapon air compression system comprising a plurality of pistons for compressing air in a compression chamber for the firing of a pellet from an air weapon, each of the pistons being integral with or connected to a movable element of a different gas spring, each of the gas springs including an expansion chamber arranged to contain a charge of compressed gas and each of the expansion chambers, being connected or connectable to at least one other thereby to balance the pressures in the connected expansion chambers at all times, the pistons and gas springs being arranged in such a configuration that the resultant of the forces due to the movement of each piston and movable element is substantially zero.

4. An air weapon air compression system as claimed in claim 3 wherein each piston is arranged, on firing, to compress air in the compression chamber.

5. A substantially recoilless air weapon in which a pellet is expelled from a barrel by air compressed within a compression chamber, the weapon including a plurality of gas springs each providing a movable piston which has a piston crown that faces, and partially defines, the compression chamber, each gas spring having an expansion chamber partially defined by its respective movable piston, the expansion chambers being capable of being filled with a charge of compressed gas, and cocking means arranged to move the pistons in directions which increase the volume of compression chamber and simultaneously further compress the gas in each expansion chamber, a gas duct being included to place each of the expansion chambers of the gas springs in communication with at least one other expansion chamber so that the forces due to the movement of connected gas springs may be substantially equal.

6. An air weapon as claimed in claim 5 including a single charging pointforthe introduction of the charge of compressed gas into the interconnected expansion chambers.

7. An air weapon as claimed in claim 5 or 6 in which the movable pistons are mechanically linked by coupling means and the cocking means is arranged simultaneously to move the pistons via the coupling means.

8. An air weapon including a barrel having an inner end into which a pellet can be loaded, an outer main cylinder including a compression chamber having an output port communicating between the compression chamber and the inner end of the barrel, the outer main cylinder having a bore containing a pair of gas springs each of which has a stationary hollow part positioned within a section of the bore of the outer main cylinder and providing an annulus between said bore and said hollow part, each gas spring also including a movable piston which is in the form of a forward hollow part which is mounted partially in the respective annulus for reciprocal movement with respect to the respective stationary hollow part, with the two hollow parts of one gas spring forming a first expansion chamber and the two hollow parts of the other gas spring forming a second expansion chamber, the movable pistons having opposed crowns which partly define the compression chamber, first sealing means being provided between the crown of each piston and the bore of the outer main cylinder, and second sealing means being provided in each gas spring between its respective hollow parts for containing a permanent charge of compressed gas in the two expansion chambers, a duct being provided permanently to place the two expansion chambers in communication with one another thereby to equalise the pressures acting on the two pistons, cocking means being provided, for moving the pistons simultaneously away from one another to reduce the expansion chamber volumes and increase the compression chamber volume, and trigger means being provided for releasing the piston simultaneously to compress the air within the compression chamber to expel the pellet.

9. An air weapon compression system, or an air weapon substantially as specifically described herein with reference to the accompanying drawings.