GB2241313A - Air gun - Google Patents

Abstract

In an air gun powered by means of a helical coil spring 1 which drives a tubular piston 2 along a cylinder 3 to provide compressed air in firing the gun, the piston is lined by a nylon sleeve 5 which prevents contact between the coils of the spring and metal inside surfaces of the piston. <IMAGE>

Description

AIR GUNS This invention relates to air guns of the well-known kind in which the gun is powered by means of a strong helical coil spring. The spring is arranged to become compressed, upon cocking the weapon, behind a piston acting within a cylinder, and the piston can then be driven forwards by the spring in firing the gun. The rapid advance of the piston compresses air in front of it within the cylinder and delivers the compressed air to the breech of the gun.

In such guns the piston is usually itself hollow and of substantial length, and when the spring is fully compressed it may be contained substantially wholly within the piston.

This construction has been widely used for many years and has proved to be generally satisfactory, but there are aspects in which improvements would be possible. For example, during cocking, relative movement between the piston and individual coils of the spring in metal-to-metal contact tends to produce audible noise. Also, in those arrangements where a cocking slide engages in a slot in the piston, the slide may ride over the individual coils of the spring on the return movement of the slide after cocking, again producing audible noise.

It has furthermore been observed that when the gun is fired the sudden expansion of the spring as it drives the piston forwards results in the spring surging axially and also oscillating laterally for several cycles immediately following completion of its travel. This can again lead to an unsatisfactory impression, being detectable as a brief vibration of the gun in the user's hand.

It has been found that these drawbacks can be overcome, or at least mitigated, by unexpectedly simple means. According to the invention an air gun of the kind which is powered by means of a helical coil spring acting within a tubular piston to drive the piston along a cylinder in firing the gun is characterised in that the piston is lined with a sleeve of a plastics material interposed between outside surfaces of the coil spring and metal inside surfaces of the piston.

The sleeve can be of nylon or any other mouldable plastics material with suitable properties. An appropriate wall thickness for the sleeve may be found to be generally within the range of 0.5mm to l.Omm, though wall thickness has not been found to be critical. The sleeve may be moulded with one end closed, the sleeve being inserted into the piston, on assembly of the gun, with the closed end at the front end of the sleeve to aid axial location of the sleeve within the piston.

The plastics sleeve may be found to give a number of unexpected advantages: a) by preventing metal-to-metal contact between the spring and the piston it can make the action of cocking both smoother and quieter; b) by preventing contact between the spring and the cocking lever or slide it may make the return motion of the lever or slide smoother and silent; c) it can damp out lateral oscillations of the spring after firing and also, by friction between the coils of the spring and the plastics inside surfaces of the sleeve, it can damp out longitudinal surges as well; d) it allows one to apply plenty of grease around the spring without any danger of the grease escaping through the slot in the piston or finding its way in front of the piston; (e) finally, long-term tests indicate that the presence of the sleeve may also increase the life of the spring significantly.This is believed to be attributable to the reduction in impacts on it by a cushioning action of the sleeve.

One embodiment of the invention is shown in the accompanying drawings by way of example.

In the drawings: Figure 1 is a view of components including a piston and cylinder device before assembly in an air rifle: and Figure 2 is a view, partially in section, of a plastics sleeve of the device.

In an air rifle of a well-known kind in which the gun is powered by means of a strong helical coil spring 1, the spring acts within a tubular cylindrical metalpiston 2 to drive the piston forwards through a cylinder 3 in firing the gun. In a conventional manner, the spring 1 is arranged to become compressed behind the piston 2 (or, more strictly, behind a front end wall 4 of the piston against which the spring reacts) upon moving the piston rearwards in cocking the weapon. In firing the gun, the piston is released to be driven forwards along the cylinder 3 by the spring.

The rapid advance of the piston compresses air in front of it within the cylinder and delivers the compressed air to the breech of the gun to drive a pellet through the barrel bore.

A cylindrical tubular sleeve 5 is formed in a mouldable plastics material having good cushioning properties (e.g. nylon). The sleeve has one end 6 closed and is open at its other end 7. Its wall thickness is within the range of 0.5mm to l.Omm.

The outer diameter of the sleeve 5 is such that the moulded sleeve can be slid into the piston to form a lining for the piston; the sleeve is preferably a snug fit within the piston, but not so tight that it would be difficult to remove for replacement if necessary.

The sleeve is of similar length to the piston, but not longer.

The inner diameter of the sleeve is such that the coil spring 1, when uncompressed, can slide readily within the sleeve and the sleeve can accommodate such diametrical expansion of the spring as occurs when it is compressed when the gun is cocked. Preferably the spring is quite a tight fit in the sleeve when compressed, for best cushioning effect.

In the assembled gun, the sleeve 5 is inserted into the piston 2 with its closed end forwards. The spring 1 is inserted into the sleeve 5 to bear at its front end against the closed end 6 of the sleeve, which in turn bears against the end wall 4 of the piston.

The sleeve is so held located axially within the piston by the spring, transmitting force axially from the spring to the piston. Apart from the introduction of the plastics sleeve 5 the gun is of a conventional construction and operates in the usual manner.

However, the sleeve, being interposed between the outside surfaces of the spring 1 and metal inside surfaces of the piston 2, prevents metal-to-metal contact between the spring and the piston and provides for the advantages referred to hereinbefore.

It will be understood that although a rifle is described the invention is equally applicable to other forms of air gun, e.g. pistols.

Claims (6)

1. An air gun of the kind which is powered by means of a helical coil spring acting within a tubular piston to drive the piston along a cylinder in firing the gun, characterised in that the piston is lined with a sleeve of a plastics material interposed between outside surfaces of the coil spring and metal inside surfaces of the piston.

2. An air gun according to claim 1 in which the spring can slide readily within the sleeve when uncompressed and is quite a tight fit within the sleeve when compressed.

3. An air gun according to either of claims 1 and 2 in which the sleeve is a snug fit within the piston but not so tight that it would be difficult to remove for replacement.

4. An air gun according to any one of claims 1 to 3 in which the sleeve is inserted into the piston with a closed front end to aid axial location within the piston.

5. An air gun according to any one of claims 1 to 4 in which the sleeve has a wall thickness within the range of 0.5mm to l.Omm.

6. An air gun substantially as hereinbefore described with reference to the accoimpanying drawings.