GB2257778A

GB2257778A - Restoring a gun barrel

Info

Publication number: GB2257778A
Application number: GB9214673A
Authority: GB
Inventors: Nigel Francis Teague
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-07-10
Filing date: 1992-07-10
Publication date: 1993-01-20
Anticipated expiration: 2012-07-10
Also published as: GB9114893D0; GB2257778B; GB9214673D0

Abstract

A method for restoring gun barrels (10), in particular shot gun barrels, whose internal surfaces have become pitted through use involves providing a lining (24) along the entire length of the gun barrel from the breech face to the muzzle end. In this way the restored barrel (10, 24) is protected by the lining (24) in the vulnerable forcing cone region of the barrel. The lining is preferably a tubular liner (24) whose outer surface (34) is complementary to an inner surface (11) of the barrel produced by machining of the barrel. The barrel and the liner are provided with complementary abutment surfaces (28, 36, 28', 36') such that movement of the liner towards the muzzle is prevented. <IMAGE>

Description

RESTORING A GUN BARREL This invention relates to a method of restoring a gun barrel, to a liner for use in the method and to a gun barrel so restored. In particular, the invention relates to restoring a shotgun barrel.

The release of shot inside the barrel of a shotgun as a result of the controlled detonation of a shotgun cartridge leads to the development of small indentations or pits on the inner surface of the shotgun barrel.

Furthermore, the inner surface of the barrel is subject to corrosion, for example as a result of interaction of the exploding gun powder and the metal of the barrel and this leads to further pitting of the surface. The pitting can become so severe that the effective thickness of the barrel walls becomes reduced. Ultimately, this leads to the gun becoming unsafe and going out of proof.

It is desirable to be able to restore shotguns to as near as possible their original state with regard to the thickness and safety of the barrel walls. Hitherto, this has been attempted in part by machining out the bore only of the barrel, and inserting a replacement liner of uniform cross-section. However, such liners do not provide any protection to the inner walls of the forcing cone, the region of the barrel where the greater crosssection of the chamber reduces to the smaller crosssection of the specified bore and such liners do not help re-establish the safety of this vulnerable region.

Further, the effectiveness and safety of the shotgun may be impaired by the wrinkling imparted by any shot which hits the protruding lip present where the liner adjoins the forcing cone.

Other small arms, such as rifles suffer from similar problems of wear incurred during use (for example wear produced by corrosion).

According to one aspect of the invention there is provided a method for restoring a gun barrel, the method comprising providing a lining on the internal surface of the barrel, the lining being provided along substantially the whole length of the barrel from the breech face to the muzzle end.

Preferably, the lining is a tubular liner for example a unitary tubular liner, which may be inserted into the barrel from the breech face.

In preferred embodiments of the method, the internal surface of the barrel is machined before provision of the lining, eg. before insertion of the liner, to increase the internal diameter of the barrel, preferably throughout substantially its entire length. Preferably, the internal surface is machined to define an abutment surface, and the liner has a complementary abutment surface which engages therewith to limit displacement of the liner along the barrel towards the muzzle. Preferably, the abutment surfaces are provided by the newly formed internal surface of the barrel and the external surface of the liner each having a profile having one or more steps.

Preferably, the internal shape of the liner corresponds to the shape of the inside of the gun barrel as it was before it became worn through use.

In some embodiments a method of restoring a gun barrel is provided which includes producing the liner by working a substantially cylindrical metal tube so that its internal shape corresponds to that of the gun barrel being restored, when that barrel was new, and so that its external surface is complementary to the machined internal surface of the barrel.

The method of the first aspect may be used for restoring any small arms but preferably, is employed for restoring shot gun barrels. A shotgun barrel comprises a chamber at the breech for receiving a cartridge, a forcing cone and a bore portion extending from the forcing cone to the muzzle. In a particular preferred embodiment a method is provided for restoring a shotgun barrel the method comprising machining the barrel of the shotgun and fitting a liner wherein the internal surface of the barrel is machined to remove a layer of the internal surface from the breech face to the muzzle end thereby to provide the internal surface with a profile of two steps, each said steps being provided in or adjacent the region of the forcing cone, for example, one said step being provided in the region of the forcing cone, the other said step being in the bore portion in a region adjacent said forcing cone. Each step includes an abutment surface.

Preferably, the method comprises three machining steps which may be carried out in any order, these steps being (i) a machining step to increase the internal diameter of the barrel in its bore portion, between the muzzle end and the forcing cone; (ii) a machining step concentric with step (i) to increase the internal diameter of the barrel in the region of the forcing cone and in a region of the bore portion adjacent the forcing cone; and (iii) a machining step concentric with (i) and (ii) to increase the diameter of the chamber, the machining step extending to a position part way along the forcing cone, thereby to produce an internal surface having a profile of two steps.

The liner is preferably produced by machining a substantially cylindrical metal tube, for example of hardened steel to provide it on its outside with surface complementary to that of the gun barrel and therefore including a pair of abutment surfaces. The tube is worked on its inside to produce an inner shape resembling that of the original gun barrel. The liner may be secured in position by a variety of methods, but the use of a curable resin adhesive for example of the cyano acrylate type such as LOCTITETM is preferred.

According to a second aspect of the invention there is provided a gun barrel as restored by the method of the first aspect.

According to a third aspect of the invention there is provided a tubular liner for inserting into a gun barrel, the internal surface of the liner defining a chamber for receiving ammunition, a frusto-conical portion adjacent said chamber and a bore portion adjacent said frusto-conical portion and remote from the chamber, the external surface of said liner being profiled to define at least one radially extending abutment surface.

The external surface of the liner preferably has the profile of at least one step thereby providing an abutment surface, the abutment surface being adapted to abut a complementary surface of the gun barrel.

Preferably, the liner is for a shotgun barrel. The liner is then preferably provided with a recess at the breechface end to allow the seating of a cartridge cap.

According to a fourth aspect of the present invention there is provided a restored gun barrel comprising a gun barrel and a liner according to the third aspect. According to a fifth aspect of the invention there is provided a gun comprising a restored gun barrel according to the fourth aspect together for example with stock, trigger, etc.

An embodiment of the present invention will now be described by way of example only with reference to the figures of which: Figure 1 shows diagrammatically a longitudinal cross-section of a barrel of a shotgun; and Figure 2 shows diagrammatically a longitudinal cross-section of the barrel of a shotgun restored according to one embodiment of the method of the present invention.

Figure 1 shows a barrel 10 which comprises a cartridge chamber 12, a forcing cone 14, and a bore portion 16 having an internal bore 17. The barrel 10 begins at breech face 20 and ends at muzzle end 22. The internal surface 11 of the barrel 10 is shown diagrammatically as being pitted, particularly in the region of the bore portion 16; the scale of the pitting is exaggerated in the drawing for clarity. Dotted line 18 indicates the profile of a surface to be machined from the internal surface 11 of the barrel.

In a first machining step a machining tool (not shown) is introduced into the internal bore 17 from the breech face 20 to machine the inside of barrel 10 radially outwardly to increase the diameter of the internal bore 17 throughout the length of the bore portion 16, thereby removing a first layer 19 of metal from its inner surface.

In a second machining step a machining tool of larger diameter than that used in the first step is introduced into the inside of the barrel 10. The internal surface 11 of the barrel is then machined radially outwardly in the region of the forcing cone 14 to remove a further layer 21 of material from the internal surface 11. During the second machining step the machining tool is pushed along the internal bore 17 towards the muzzle end 22 so that the internal diameter of the bore 17 is further increased at the end of the bore portion 16 adjacent the forcing cone 14. The internal surface of the bore portion 16 therefore has the profile of a step 28 adjacent forcing cone 14.

In a third machining step a machining tool of still larger diameter is introduced into the inside of the chamber 12 and a further layer 23 of material is removed.

This machining step extends part way into the region of the forcing cone so that a further step 28' is formed in the profile of the newly formed internal surface of the barrel 10.

The distance between the first step 28 and the breech face 20 is designated B in the figure while that between the second step 28' and the breech face 20 is designated A.

Figure 2 shows a machined barrel 10 with a liner 24 in place. The liner can be introduced into the machined barrel 10 from the breech face 20. The liner 24 is machined from a hardened steel tube so that its internal surface 30 corresponds in shape to the shape of that of the gun when new. On its outer surface 34 the liner is provided with a profile of two steps 36, 36', which correspond in size and position to those on the newly machined internal surface 26 of the barrel 10. There is a small clearance 38 between the outer surface 34 of the liner 24 and the internal surface 26 of the barrel 10 which is filled with adhesive or solder to hold the liner 24 in place. In most cases, a suitable clearance 38 would be of the order of 1/1000-2/1000".

In the case of a 12 gauge shotgun the first machining step is used to increase the internal bore 17 in the bore portion 16 to a diameter of around 3/4". The selected diameter for this machining step varies depending on the gauge of the shotgun being renovated.

The diameters produced in the second and third machining steps and the consequent sizes of the steps 28, 28' on the internal surface 26 of the machined barrel 10 are chosen according to the gauge of the shotgun and the length of the chamber of the gun being modified. In the case of a 12 gauge gun the diameter of the inside of the barrel 10 in the region of the second machining would be around 13/16" and in that of the third machining would be around 7/8". Diameters achieved in the second machining step vary between 3/4" and 55/64", and in the third step between 51/64" and 29/32" depending on the shotgun being modified.

For most shotguns, machining would be carried out such that the length A would be within the range 3 to 4", while length B would be chosen to be within the range 4 to 5" for example, in the case of a 12-gauge shotgun, length A would be about 3" and length B about 4".

The liner for a 12 gauge gun has typical thicknesses designated x, y and z in the figures of 15/1000" in its bore portion, 20/1000" in the forcing cone and 25/1000" in the chamber. Desirably, the thickness of the liner in the vicinity of the second step, 28', 36' is made as large as practicable.

Claims

CLAIMS:

1. A method for restoring a gun barrel, comprising providing a lining on the internal surface of the barrel, the lining being provided along substantially the whole length of the barrel from the breech face to the muzzle end.

2. A method according to claim 1 wherein the internal surface of the barrel is machined throughout substantially its entire length to increase the internal diameter of the barrel prior to provision of the lining.

3. A method according to claim 2 wherein the lining is a tubular liner, which is insertable into the barrel from the breech face.

4. A method according to claim 3 wherein the internal surface of the barrel is machined to provide at least one abutment surface and the liner has at least one complementary abutment surface which engages with the at least one abutment surface of the barrel to limit displacement of the liner along the barrel towards the muzzle.

5. A method according to claim 4 wherein the at least one abutment surface of the barrel and the at least one complementary abutment surface of the liner are provided by the internal surface of the barrel and the outer surface of the liner each having a profile having one or more steps.

6. A method according to any one of claims 3 to 5 wherein the internal shape of the liner corresponds to the shape of the inside of the gun barrel when new.

7. A method according to any one of claims 3 to 6 further comprising producing the liner by working a substantially cylindrical metal tube so that its internal shape corresponds to that of the inside of the gun barrel when new and its external surface is complementary to the internal surface of the gun barrel at the time of insertion of the liner.

8. A method according to any one of the preceding claims wherein the gun barrel is that of a shotgun.

9. A method according to any one of claims 3 to 8 wherein the gun barrel includes a forcing cone, comprising machining the internal surface of the barrel to remove a layer of the internal surface from the breech face to the muzzle end to provide the internal surface with a profile of two steps, each said step being in or adjacent the region of the forcing cone, thereby to provide a pair of abutment surfaces on the internal surface; and inserting a liner whose outer surface has a profile complementary to that of the internal surface of the barrel.

10. A method according to claim 9 wherein the machining comprises the steps of: (i) machining the internal surface of the barrel to increase the internal diameter of the barrel in its bore portion, between the muzzle end and the forcing cone; (ii) machining the internal surface of the barrel to increase the internal diameter of the barrel in the region of the forcing cone and in a region of the bore portion adjacent the forcing cone; and (iii) machining the internal surface of the barrel to increase the diameter of the barrel in the chamber, the machining extending to a position part way along the forcing cone; each of said machining steps producing a substantially cylindrical machined portion which is substantially concentric with the machined portion produced in the other two steps.

11. A method for restoring a gun barrel substantially as herein described with reference to and as illustrated in the accompanying drawings.

12. A gun barrel as restored by the method of any one of claims 1 to 11.

13. A tubular liner for insertion into a gun barrel, the internal surface of the liner defining a chamber for receiving ammunition, a frusto-conical portion adjacent said chamber and a bore portion adjacent said frustoconical portion and remote from the chamber, the external surface of said liner being profiled to define at least one radially extending abutment surface.

14. A restored gun barrel comprising a gun barrel and a liner according to claim 13.

15. A gun having a restored gun barrel according to claim 14.

16. A liner, restored gun barrel, or gun, substantially as herein described with reference to and as illustrated in the accompanying drawings.