GB2104197A - Air gun silencers - Google Patents

Abstract

A silencer specifically for air guns is provided with a series of internal baffles formed from thermoplastic material that would melt or distort at the muzzle discharge temperature of a firearm. An adaptor (20) to which the silencer (10) is screw-threaded is force-fitted on a portion of the gun barrel (1) extending from its mouth beyond the barrel foresight mounting location, the foresight having been removed from the barrel and a foresight or foresight mounting (26a) being provided on the adaptor (20). <IMAGE>

Description

SPECIFICATION Air gun silencers The invention relates to air gun silencers.

Conventional silencers for firearms are fitted over the muzzle ofthe firearm and there present, at the end of the barrel, an expansion chamber for the propulsion gases, followed by a series of baffles between the expansion chamber and the muzzle of the silencer. The baffles slow down the propulsion gases as they pass to the atmosphere after the shot has been fired, and thus achieve their silencing effect. The silencer itself is anchored to the gun muzzle by engaging an internally screw-threaded portion of the silencer with a male screw thread that is cut around the barrel. In many countries the sale of such silencers for firearms is subject to stringent conditions or is possible only under licence. A recent development in the sale of silencers is the introduction of our own range of silencers for air weapons.

The most powerful air weapons have muzzle velocities that are fully comparable with those of some firearms, including rifles. These silencers are not screw-threaded onto the barrel of the gun, but are a friction fit around the muzzle. This means that each silencer has to be made to a particularly high standard of accuracy, and matched to a particular gun barrel size and type. The intention behind this method of fitting is that the silencers cannot be used with firearms, since the hot propulsion gases of the firearm would push the silencer off the end of the barrel. Furthermore, the internal baffles of the air gun silencer have been made of thin metal with the intention that they would rupture or collapse if used on a firearm, thereby ensuring that the silencers are used exclusively for air weapons.

One disadvantage of the above air weapon silencers has been that because each silencer is matched closely to a particular barrel size and type, the silencers are not interchangeable for anyone who has more than one weapon. A second disadvantage is that if the silencers are constantly fitted and removed, they can become worn so that the efficiency of the friction fit on the barrel is reduced.

These problems are both overcome by our current range of silencer assemblies. Each assembly comprises a silencer and an adaptor wherein the adaptor is provided with a stepped bore passing completely therethrough, of which a larger diameter portion is designed for fitting around an end portion of the gun barrel as a friction fit, with an internal shoulder of the stepped bore abutting the end ofthe gun barrel, and a smaller diameter portion that is screw-threaded to receive a male screw thread on the end of the silencer. The screw-thread on the smaller diameter portion is preferably internal, and that on the silencer external, but the opposite arrangement is possible.

The advantages of this arrangement are many and varied. The most immediate advantage is that the adaptor can be machined very accurately to fit a particular gun barrel size and type, and once placed on that barrel need never be removed. The silencer can be screwed into and unscrewed from the adaptor relatively easily without damage to the efficiency of the friction fit. Moreover, the screw thread size and pitch on the silencer may be made standard, so that the same silencer can be used with any of a number of adaptors, each adaptor being made to suit and being fitted to a particular gun barrel.

One advantageous feature of the above system of adaptor-and-silencer is that the male screw-threaded portion of the silencer may be designed so that it does not extend the full length of the smaller diameter portion of the stepped bore. Thus when the adaptor is fitted on a gun barrel and the silencer is screwed thereinto, a small pre-expansion chamber is provided for the propulsion air or gases, in advance of the main chamber in the silencer. This assists the silencing action, and the additional chamber can be achieved without the need for any extra machining during manufacture.

One disadvantage of the adaptors previously proposed is that they need to be fitted onto the barrel of the weapon at the same location as the foresight of the weapon. This has been avoided either by locating the adaptor forwardly of the foresight or by creating an axial slit in the adaptor to enable the foresight to extend therethrough. The former solution provides a severe restriction on the axial length of the mounting of the adaptor, and the latter solution weakens the friction fit between the adaptor and the barrel due to the inherent flexibility of the material from which the adaptor is made. In either case the result is a tendencyforthe silencer to impairthe accuracy of the weapon due to imprecise axial location.

This invention provides a solution to the above problem while maintaining all ofthe preferred features ofthe adaptor-and-silencer system. The invention provides a silencer assembly for an air gun, comprising a silencer and an adaptorforscrew- threadly attaching the silencer to the barrel of the gun, wherein the adaptor comprises a screwthreaded end portion for mounting the silencer, a portion providing a foresight or foresight mounting and a full sleeve portion for friction fitting, after removal of the barrel foresight of the gun, on an end portion ofthe gun barrel which end portion extends from the mouth of the barrel past the barrel foresight mounting location.Because the friction fit between the adaptor and barrel can be extended down the barrel of the weapon past the foresight location, the axis alignment of the silencer is made much more precise. Moreover the adaptor is much less likely to move on the barrel under normal conditions of use, and yet surprisingly still retains the characteristic that it can be made to an accuracy of fit such that it would be forced off the barrel if used on an air weapon with a muzzle energy of more than 20 foot pounds per square inch.

Although all of the above provisions are intended to create a silencer or silencer assembly that is par ticularly suitable for air weapons as opposed to firearms, it is a matter of utmost concern that the same silencers may be capable of being used with firearms. The invention accordingly further provides a silencer assembly of which it can be said that use with any kind firearm is quite impossible. The silencer of an assembly according to the invention therefore preferably contains a series of apertured baffles each of which is made of a thermoplastic material that is sufficiently low-melting to lose its shape if subjected to the heat of the discharge gases of a firearm.In this way there is provided a silencer chamber which will be completely destroyed the first time it is used on a firearm barrel but which has a full and effective service life on air weapons.

The loss of shape of the baffles under the heat of a firearm discharge ensures that the silencers of the invention are incapable of effective use even once on a firearm. The loss of shape may be by total fusion of the thermoplastic material ofthe baffles or it may simply be that the baffles, brought to a temperature above their softening temperature, have an elastic memory that causes them rapidly to assume some other shape and to lose the aligment of the central apertures. Preferably the silencer is made as a sealed unit so that after assembly and sale the baffles cannot be removed.

The effective use of silencers of the invention on air guns with a muzzle energy of more than 20 foot pounds per square inch (which weapons require a firearms certificate for the weapons themselves and for attachments therefor) is prevented by reducing the tensile strength of the baffles until they would rupture under the conditions of such high muzzle velocities, and/or by controlling the efficiency of the friction fit between the silencer adaptor and the gun barrel until it can reliably be said that the silencer would not stay on the barrel at such high muzzle velocites.

The material to be used for the baffles may be any thermoplastic material, preferably with a good elastic memory. Polypropylene, polystyrene and high density polyethylene are examples of suitable materials. The baffles may be made by injection-moulding and/or by hot stamping, the latter being preferred as a means for introducing the internal stresses needed to take advantage of the elastic memory properties.

The cylinder may also be made of thermoplastic material, although aluminium tubing is preferable with plastics plugs at the ends. Adaptors for fitting the silencer onto different gun barrels may be cast but are preferably machined from a solid block of aluminium or plastics material such as nylon.

Each of Figures 1 and 2 of the drawings is an axial section through a silencer assembly according to the invention, fitted on the barrel of an air rifle. The silencers ofthe different assemblies are identical, but the adaptors are shown as having different shapes to suit them for the different air rifles shown.

Referring first to Figure 1, a muzzle end portion of a rifle barrel 1 is shown, with its foresight removed.

Onto the barrel is fitted a silencer assembly compris ing a silencer 10 and an adaptor 20. The silencer 10 comprises a male screw-threaded end fitting portion 12, an expansion chamber 14 that occupies about 50 h of the length of the silencer, and a series of baffles 16 at the nozzle end of the silencer. Each of the baffles 16 has a central aperture, these being aligned so as to provide a continuous passage through the silencer for projectiles fired from the air rifle. Each baffle is provided with two dimpled portions 18, the dimples being formed from opposite sides ofthe baffle. The angular orientation ofthe dimpled portions is varied between successive baffles 16, which is the reason why only the right hand end baffle is shown as being dimpled in Figure 1.

The reason for this angular disposition of dimples is that it improves the braking effect of air passing from the expansion or blast chamber 14, and improves the silencing characteristics of the silencer. The baffles 16 are made from polypropylene or polystyrene by hot-stamping from the sheet followed by immediate quenching, and their internal stresses are such that they would distort substantially if subjected even once to the blast and temperature of the propulsion gases at the muzzle of a firearm. Also, the tensile strength of the baffles 16 is such that they would not withstand use on a firearm, so that the silencer 10 is inherently one for use with air weapons. The whole of the silencer is force-fitted together so as to provide a sealed unit that cannot be opened for cleaning purposes.

The adaptor 20 has a bore therethrough comprising a smaller diameter screw-threaded portion 22 and a larger diameter portion 24 with a shoulder 23 therebetween. The smaller diameter portion 22 is internally screw-threaded to receive the male screw-threaded portion 12 of the silencer 10.

The adaptor 20 may be made from a hard plastics material such as high impact polyvinylchloride, and is preferably machined from a solid bar so as to obtain an accurate fit with the barrel 1.

The assembly of Figure 1 is for fitting to the barrel 1 of a Sharp Innova pneumatic airgun, which has a pump mechanism 3 below the barrel. The adaptor is formed with an integral foresight 26 to replace the foresight of the rifle barrel which is removed, and has a lower mounting portion 28 formed integrally with the remainder of the adaptor, for insertion into and anchorage within the pump mechanism.

The silencer assembly of Figure 2 are very similar in construction to that of Figure 1,so to avoid repetition only the differences will be described.

The assembly of Figure 2 incorporates a foresight 26a provided not on the barrel 1 of the rifle but on the adaptor 20. This is desirable when the foresight suppled with the rifle is not sufficiently high to be visible above the silencer, and removal of the foresight from the barrel does enable the adaptor to be force-fitted over a greater length of the barrel.

Each of the adaptors shown in the drawings may be made of metal alloy or of hard plastics material such as high impact polyvinylchloride. A particularly suitable method of ensuring a good friction fit between the barrel and the adaptor is available when the adaptor is made of alloy, and involves heating the adaptor prior to fitting, so that as it cools it contracts and clamps more firmly onto the barrel.

Claims (11)

1. A silencer assembly for an air gun, comprising a silencer and an adaptor for screw-threadly attaching the silencer to the barrel of the gun, wherein the adaptor comprises a screw-threaded end portion for mounting the silencer, a portion providing a foresight or foresight mounting and a full sleeve portion for friction fitting, after removal of the barrel foresight of the gun, on an end portion of the gun barrel which end portion extends from the mouth of the barrel past the barrel foresight mounting location.

2. A silencer assembly according to claim 1, wherein the silencer contains a series of apertured baffles each of which is made of a thermoplastic material that is sufficiently low-melting to lose its shape if subjected to the heat of the discharge gases of a firearm.

3. A silencer assembly according to claim 2, wherein the baffles are made from an internally stressed thermoplastic material that has an elastic memory, so that heating the baffles to above their softening temperature causes them rapidly to assume some other shape and to lose the alignment of their apertures.

4. A silencer assembly according to claim 2 or claim 3, wherein the tensile strength of the baffles is such that they would rupture if subjected to muzzle velocities of more than 20 foot pounds per square inch.

5. A silencer assembly according to any of claims 2 to 4, wherein the baffles are made from polypropylene, polystyrene or high density polyethylene.

6. A silencer assembly according to any of claims 2 to 5, wherein the baffles are made by injection moulding and/or by hot stamping.

7. A silencer assembly according to any of the preceding claim wherein the adaptor is made of a hard plastics material.

8. A silencer assembly according to claim 7, wherein the adaptor is machined from a solid block of high impact polystyrene.

9. A silencer assembly according to any of claims 1 to 7, wherein the adaptor is made by casting.

10. A silencer according to any preceding claim, wherein the screw-threaded end portion of the adaptor carries a female screw-thread for receiving a male screw-thread on the silencer.

11. A silencer assembly for air guns, substantially as described herein with reference to the drawings.