Choke for gun barrels and method for modifying a choke

Abstract

The invention relates to a method for modifying a choke (5) for a smoothbore shotgun barrel (1), comprising the following steps: - providing a choke (5) having a through orifice (6) delimited by an internal surface (7), the internal surface (7) comprising a conical portion (8) and a cylindrical portion (9) with a circular cross-section, the conical portion (8) and the cylindrical portion (9) extending over a dimension equal to a predetermined length L, - introducing a conical reamer (12) into the through orifice (6) on the side of the conical portion (8), - machining, using the conical reamer (12), the internal surface (7) of the choke (5) so that, after machining, the internal surface (7) has a conical shape extending in the first direction over the entire predetermined length L. The invention also relates to chokes (5) for smoothbore shotgun barrels (1). Figure for the abstract: 6

Description

Title of the invention: Choke for rifle barrel and method of modifying a choke Technical field

[0001] The invention relates to the field of chokes for smoothbore shotgun barrels. The invention relates more particularly to methods of modifying chokes for this type of shotgun as well as the chokes as such. Technological background

[0002] Chokes for smoothbore shotgun barrels are known from the prior art. The choke, or also called a constriction, can be removably attached to the muzzle of the barrel, or also called the distal end of the barrel relative to the ammunition chamber; this type of choke is thus called an "interchangeable" choke. The choke can also be an integral part of the barrel; this type of choke is then called a "fixed" choke.

[0003] The choke is a slight tightening of the muzzle of the barrel allowing the spray of balls contained in the ammunition to be concentrated more or less strongly. There are different types of choke depending on the intensity of the tightening. The choke's role is to provide an ideal quality of spray grouping at a given distance.

[0004] Document FR912871 describes in particular chokes of the prior art. The chokes of this document comprise a through orifice comprising a conical portion and a cylindrical portion with a circular section. The conical portion makes it possible to pass from the internal diameter of the barrel, called the "bore diameter", to the diameter of the cylindrical portion with a circular section which represents the internal diameter at the outlet of the choke. The internal diameter at the outlet of the choke is less than the bore diameter. The conical portion thus serves to tighten the shower of balls while the cylindrical portion serves to stabilize the shower of balls at the outlet.

[0005] Figures 1 and 2 represent in particular a barrel 1 comprising a fixed choke 4 of the prior art.

[0006] Ammunition for this type of rifle is currently mainly composed of lead balls. However, ammunition composed of steel balls is replacing lead ball ammunition.

[0007] However, due to the greater hardness of steel compared to lead, steel balls are not suitable for FR912871 chokes. In fact, when passing between the conical portion and the cylindrical portion, the steel balls exert a significant force on the choke which causes swelling, weakening the choke and the cannon.

[0008] This type of choke is therefore not usable for steel ball ammunition. However, when the choke is an integral part of the rifle and in the event of an obligation to use steel ball ammunition, a good number of weapons on the market can no longer be used.

[0009] Document EPI643204 describes chokes which, according to the document, would allow in particular the use of steel ball ammunition. The chokes of this document have a first conical portion which tightens the diameter followed by a second conical portion which this time increases the diameter.

[0010] However, these chokes are also not entirely satisfactory for the use of steel ball ammunition. On the one hand, the passage from the first conical portion to the second conical portion generates, as previously for FR912871, during the passage of the steel balls a significant force which causes a swelling weakening the choke and the barrel. On the other hand, by widening the outlet diameter of the choke with the second conical portion, the steel balls lose speed and the outlet pattern is increased. In addition, it is thus not possible to obtain chokes with a strong pattern tightening, called "full chokes". Summary of the invention

[0011] One idea behind the invention is to adapt existing weapons and chokes to the use of steel ball ammunition.

[0012] Another idea underlying the invention is to limit the stresses in the choke when using steel ball ammunition, while maintaining a high exit velocity.

[0013] According to one embodiment, the invention relates to a method of modifying a choke for a smoothbore shotgun barrel, in which the method comprises the following steps: - providing a choke for a smoothbore shotgun barrel, the choke having a through-orifice delimited by an internal surface, the internal surface comprising successively in the first direction, from an inlet to an outlet of the choke, a conical portion and a cylindrical portion with a circular section, the conical portion and the cylindrical portion extending in the first direction over a dimension equal to a predetermined length L, - insert a conical reamer into the through hole on the side of the conical portion, - machine the internal surface of the choke using the conical reamer so that after machining the internal surface has a conical shape extending in the first direction over the entire predetermined length L.

[0014] Thanks to these characteristics, by machining the internal surface of existing chokes, it is possible to eliminate the interface between the conical portion and the cylindrical portion of the choke while maintaining the same difference in diameter between the inlet and outlet of the choke. Thus, the stresses in the choke are limited, which prevents any swelling when using steel shot ammunition. In addition, since the conical shape is made along the entire length of the choke, the reduction in diameter is achieved gradually, also contributing to reducing stresses. Finally, surprisingly, the absence of a cylindrical portion in the choke does not affect the stability of the choke and even allows for a higher exit velocity of the balls, and therefore greater penetrating power.

[0015] According to one embodiment the invention also provides a choke for a smoothbore shotgun barrel, in which the choke comprises a through orifice delimited by an internal surface, the internal surface having a predetermined length L in a first direction, the internal surface having a conical shape over the entire predetermined length L.

[0016] Thanks to these characteristics, the conical internal surface along the entire length of the choke makes it possible to limit the stresses in the choke exerted by the steel balls compared to a choke comprising a conical portion and a cylindrical portion. Furthermore, surprisingly, the absence of a cylindrical portion in the choke does not harm the stability of the choke and even makes it possible to obtain a higher exit speed of the balls, and therefore with a greater penetrating power.

[0017] According to embodiments, such a method or such a choke may comprise one or more of the following characteristics.

[0018] According to one embodiment, during the supply step, the choke is supplied with a smoothbore shotgun barrel comprising a tubular main body having a proximal end forming an ammunition chamber and a distal end, the choke being connected to the tubular main body in the extension of the distal end, and in which during the introduction step, the conical reamer is inserted through the proximal end.

[0019] According to one embodiment, the choke comprises at one end a coupling device configured to cooperate with a barrel support device located at one end of the barrel.

[0020] According to one embodiment, the choke comprises at one end a coupling device and the distal end of the tubular main body comprises a support device, the coupling device and the support device being configured to cooperate with each other.

[0021] According to one embodiment, the choke and the main body are made in a single piece.

[0022] According to one embodiment, the conical reamer is a roughing conical reamer, and the machining step comprises a first pass carried out with the conical reamer roughing and a second pass following the first pass and carried out with a finishing conical reamer, the finishing conical reamer having a maximum diameter greater than a maximum diameter of the roughing conical reamer.

[0023] Thus, by carrying out two passes, it is possible to obtain a superior machining quality and therefore the surface condition of the internal surface so as to limit the friction of the balls.

[0024] According to one embodiment, the roughing conical reamer has a rectilinear generatrix inclined relative to the axis of the roughing conical reamer, and the finishing conical reamer has a rectilinear generatrix inclined relative to the axis of the finishing conical reamer, the inclination of the generatrix of the roughing conical reamer being equal to the inclination of the generatrix of the finishing conical reamer.

[0025] According to one embodiment, after the machining step, the method comprises a polishing step during which a polishing tool is inserted into the through-orifice of the choke in order to polish the internal surface of the choke, the internal surface of the choke having, after polishing, a conical shape defined by a curvilinear generatrix.

[0026] Thus, by polishing the internal surface, the surface condition of the internal surface is improved. In addition, the conical shape with curvilinear generator makes it possible to further limit the stresses in the choke.

[0027] According to one embodiment, the curvilinear generator has a concavity.

[0028] According to one embodiment, the curvilinear generator has an angle with the axis of the through hole which increases from the inlet to the outlet of the choke.

[0029] Thus, the tightening of the diameter in the choke is progressive and increases as one moves away from the barrel.

[0030] According to one embodiment, during the machining step, the conical reamer is fixed on a machining machine comprising a rotary shaft connected to a motor using a mechanical transmission, the conical reamer being fixed to a first end of the rotary shaft, a second end of the rotary shaft being fixed to the mechanical transmission using a ball joint.

[0031] Thus, using the ball joint, it is possible to more easily align the axis of the conical reamer with the axis of the through hole in order to ensure that the machining will be carried out while retaining the initial axis of the through hole.

[0032] According to one embodiment, the conical shape is defined by a curvilinear generator.

[0033] Thus, the curvilinear shape and the more gradual reduction in diameter also contribute to reducing the stresses in the choke.

[0034] According to one embodiment, the predetermined length L is between 50 mm and 120 mm, preferably between 90 and 100 mm.

[0035] According to one embodiment, the through orifice has an inlet diameter of choke and a choke outlet diameter, the difference between the choke inlet diameter and the choke outlet diameter being between 0.2 and 1 mm.

[0036] According to one embodiment, one end of the choke comprises a coupling device configured to cooperate with a support device located at one end of a smoothbore barrel.

[0037] According to one embodiment, the invention also provides a smoothbore shotgun barrel, in which the barrel comprises a tubular main body having a proximal end forming an ammunition chamber and a distal end, the barrel comprising a aforementioned choke, the choke being formed in the extension of the distal end of the tubular main body, the choke and the main body being produced in a single piece. Brief description of the figures

[0038] The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes, with reference to the appended drawings.

[0039] [Fig. 1] represents a sectional view of a smoothbore shotgun barrel comprising a choke according to the prior art.

[0040] [Fig.2] represents a view of detail II of [Fig.l], illustrating in particular the choke of the prior art.

[0041] [Fig. 3] represents a sectional view of a smoothbore shotgun barrel comprising a choke according to one embodiment, after the machining step.

[0042] [Fig.4] represents a view of detail IV of [Fig.3], illustrating in particular the choke according to one embodiment.

[0043] [Fig. 5] represents a sectional view of a smoothbore shotgun barrel comprising a choke according to one embodiment, after the polishing step.

[0044] [Fig.6] represents a view of detail VI of [Fig.5], illustrating in particular the choke according to one embodiment.

[0045] [Fig.7] represents a sectional view of a smoothbore shotgun barrel equipped with a removable choke according to one embodiment.

[0046] [Fig.8] shows a front view of a plurality of conical reamers of different diameters used for the step of machining the internal surface of the choke according to one embodiment.

[0047] [Fig.9] shows a front view of an expanding stone polishing tool used for the step of polishing the internal surface of the choke according to one embodiment. Description of the embodiments

[0048] As seen previously in the technological background section, Figures 1 and 2 show a smoothbore shotgun barrel 1 according to the prior art. The barrel 1 has an axis of revolution and extends in a direction X. The barrel 1 comprises a tubular main body 2 having a proximal end forming an ammunition chamber 3 and a distal end. In [Fig.l], ammunition 4 is shown in the chamber 3. In the case of a fixed choke illustrated in [Fig.l], the barrel 1 comprises a choke 5 formed in the extension of the distal end of the tubular main body 2. The choke 5 and the main body 2 are thus here produced in a single piece.

[0049] Also, as seen more particularly in [Fig.2], the choke 5 of the prior art has a through orifice 6 delimited by an internal surface 7. The internal surface 7 comprises in the direction X, from an inlet to an outlet of the choke 5, a conical portion 8 and a cylindrical portion 9 with a circular section. The addition of the dimension of the conical portion and the cylindrical portion in the direction X is equal to a predetermined length L representing the length L of the choke 5. Thus, the inlet diameter 10 of the choke 5 corresponds to the start of the conical portion 8 and is equal to the core diameter of the main body 2, while the outlet diameter 11 of the choke 5 corresponds to the diameter of the cylindrical portion 9 and is strictly less than the core diameter of the main body 2.

[0050] The invention aims in particular to modify the chokes 5 of the prior art but also to produce barrels 1 and chokes 5 as such as will be seen subsequently with reference to figures 3 to 9. These modifications and these designs make it possible to use the chokes 5 on ammunition 4 with steel balls by limiting the stresses in the choke 5 and thus avoiding any risk of swelling.

[0051] The method of modifying the chokes 5 thus aims to start from a choke 5 of the prior art comprising both a conical portion 8 and a cylindrical portion 9 and to machine it to remove the cylindrical portion 9.

[0052] For this, it is planned to introduce a conical reamer 12 by inserting it: - either in the case of an interchangeable choke alone, directly into the through-hole 6 of the choke 5 on the side of the conical portion 8, - either in the case of a choke (fixed or interchangeable) connected to the main body 2 of the barrel 1, via the proximal end forming the chamber 3 of the main body 2.

[0053] This conical reamer 12 is illustrated in particular in [Fig.8]. There are a plurality of different conical reamers depending on the bore diameter of the barrel 1 and on the other hand on the desired tightening of the choke 5, which in fact influences the slope of the generatrix of the conical reamer 12.

[0054] The conical reamer 12 is fixed on a machining machine (not shown, for example a boring bench) comprising a rotating shaft connected to a motor using a mechanical transmission. The conical reamer 12 is fixed to a first end of the rotating shaft, a second end of the rotating shaft being fixed to the mechanical transmission using a ball joint, so as to form a loose chuck. Thanks to this ball joint (or more simply a pivot connection with rotational clearances allowing the rotating shaft to be offset), it is possible to place the conical reamer 12 in the axis of the barrel 1 or the through hole 6 more easily so as to ensure that the machining will be carried out while maintaining the initial axis of the barrel 1 or the through hole 6.

[0055] Following the introduction of the conical reamer 12, the machining of the internal surface 7 of the choke 5 is carried out by rotating the conical reamer 12.

[0056] Figures 3 and 4 show as an example a fixed choke 5 of a barrel 1 which has been machined according to the modification method. Thus, after machining and as visible in particular in [Fig.4], the internal surface 7 has a conical shape extending in the direction X over the entire predetermined length L. The generatrix of this conical shape is rectilinear and corresponds to that of the conical reamer 12 used.

[0057] Advantageously, the machining step of the modification method is carried out in two passes, namely a first pass carried out with a roughing conical reamer and a second pass following the first pass and carried out with a finishing conical reamer. The finishing conical reamer has a maximum diameter slightly greater than the maximum diameter of the roughing conical reamer, for example of the order of 0.2 mm greater, so as to obtain a higher machining quality. Thus, for a core diameter of 18.4 mm, the maximum diameter of the finishing conical reamer will be approximately 18.35 mm while the maximum diameter of the roughing conical reamer will be approximately 18.15 mm.

[0058] In addition, the inclination of the generatrix of the roughing conical reamer is equal to the inclination of the generatrix of the finishing conical reamer so as to maintain the desired initial tightening.

[0059] Preferably, and following the machining, the method comprises a polishing step during which a polishing tool 13 is inserted into the through-orifice 6 of the choke 5 in order to polish the internal surface 7 of the choke 5 and thus improve the surface condition of the internal surface 7. Following the polishing, the internal surface 7 of the choke 5 has a conical shape defined by a curvilinear generatrix.

[0060] As an example, the polishing tool 13 used may be, as shown in [Fig.9], a polishing head with expanding stones. This tool 13 thus comprises a rotating shaft 14 and stones 15 fixed in grooves of the rotating shaft 14. The rotating shaft 14 is connected to a pressurization system which makes it possible to separate the stones 15 radially so that they protrude more or less from the rotating shaft 14 depending on the pressure used. It is these stones 15 which will, by friction, polish the internal surface 7 of the choke 5. The stones 15 will, over the course of use, wear more significantly at the outlet of the choke 5 due to the smaller diameter. Thus, the stones 15 will present a curvilinear profile with a concavity. This profile will influence the shape of the internal surface 7.

[0061] Figures 5 and 6 illustrate as an example a fixed choke 5 of a barrel 1 which has been polished according to the modification process. Thus, it is possible to distinguish in [Fig.6] that after polishing, the internal surface 7 has a conical shape extending in the direction X over the entire predetermined length L and whose generatrix of this conical shape is curvilinear with a concavity influenced by the stones 15, so that the angle of the generatrix with the axis of the through-orifice 6 will be increasing from the inlet to the outlet of the choke 5.

[0062] Figures 3 to 6 have illustrated as an example a fixed choke 5 of a barrel 1 having been modified by the modification method. [Fig.7] illustrates another example in which it is an interchangeable choke 5 which can be coupled with a main body 2 of a barrel 1. In this case, the choke 5 comprises a coupling device 16 made at one of its ends or on its external surface, for example a screw thread, which cooperates with a support device 17, for example a screw thread, made on the distal end or inside a housing of the main body 2. In the illustrated case, the interchangeable choke 5 is inserted inside a housing of the main body 2. In other embodiments, the interchangeable choke 5 can also partially or completely protrude from the main body 2 depending on how the coupling device 16 cooperates with the support device 17.

[0063] The fixed choke and the interchangeable choke described above with reference to Figures 3 to 7 have been described as being chokes having been modified using the modification method on chokes of the prior art. However, the chokes of the invention can also be designed directly during the manufacture of the barrel or the choke.

[0064] Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0065] The use of the verb “comprise”, “comprise” or “include” and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0066] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims

Claims

1. Method for modifying a choke (5) for a smoothbore shotgun barrel (1), wherein the method comprises the following steps: - providing a choke (5) for a smoothbore shotgun barrel (1), the choke (5) having a through-orifice (6) delimited by an internal surface (7), the internal surface (7) successively comprising in the first direction, from an inlet to an outlet of the choke (5), a conical portion (8) and a cylindrical portion (9) with a circular cross-section, the conical portion (8) and the cylindrical portion (9) extending in the first direction over a dimension equal to a predetermined length L, - introducing a conical reamer (12) into the through-orifice (6) on the side of the conical portion (8), - machining using the conical reamer (12) the internal surface (7) of the choke (5) so that after machining the internal surface (7) has a conical shape extending in the first direction over the entire predetermined length L.

2. A method of modifying a choke (5) according to claim 1, wherein in the providing step, the choke (5) is provided with a smoothbore shotgun barrel (1) comprising a tubular main body (2) having a proximal end forming an ammunition chamber (3) and a distal end, the choke (5) being connected to the tubular main body (2) in the extension of the distal end, and wherein in the introducing step, the conical reamer (12) is inserted through the proximal end.

3. A method of modifying a choke (5) according to claim 1 or claim 2, wherein the conical reamer (12) is a roughing conical reamer (12), and the machining step comprises a first pass made with the roughing conical reamer (12) and a second pass following the first pass and made with a finishing conical reamer (12), the finishing conical reamer (12) having a minimum diameter greater than a minimum diameter of the roughing conical reamer (12).

4. Method for modifying a choke (5) according to one of claims 1 to 3, wherein after the machining step, the method comprises a polishing step during which a polishing tool (13) is inserted into the through-hole (6) of the choke (5) in order to polish the internal surface (7) of the choke (5), the internal surface (7) of the choke (5) having, after polishing, a conical shape defined by a curvilinear generatrix.

5. A method of modifying a choke (5) according to one of claims 1 to 4, wherein during the machining step, the conical reamer (12) is fixed to a machining machine comprising a rotary shaft connected to a motor using a mechanical transmission, the conical reamer (12) being fixed to a first end of the rotary shaft, a second end of the rotary shaft being fixed to the mechanical transmission using a ball joint.

6. Choke (5) for a smoothbore shotgun barrel (1), wherein the choke (5) comprises a through-orifice (6) delimited by an internal surface (7), the internal surface (7) having a predetermined length L in a first direction, the internal surface (7) having a conical shape over the entire predetermined length L, the conical shape being defined by a curvilinear generatrix having a concavity, the curvilinear generatrix having an angle with an axis of the through-orifice which increases from an inlet to an outlet of the choke.

7. Choke (5) according to claim 6, wherein the predetermined length L is between 50 mm and 120 mm, preferably between 90 and 100 mm.

8. A choke (5) according to claim 6 or claim 7, wherein one end of the choke (5) comprises a coupling device (16) configured to cooperate with a support device (17) located at one end of a smoothbore barrel (1).

9. Barrel (1) of a smoothbore shotgun, in which the barrel (1) comprises a tubular main body (2) having a proximal end forming an ammunition chamber (3) and a distal end, the barrel (1) comprising a choke (5) according to claim 6 or claim 7, the choke (5) being formed in the extension of the distal end of the tubular main body (2), the choke (5) and the main body (2) being made in a single piece.

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