SHOTGUN CARTRIDGE CASE-SLEEVE AND A CARTRIDGE MADE THEREFROM

Abstract: The invention relates to a shotgun cartridge case and to a shotgun cartridge made therefrom. The case is made in one piece from injection-moulded plastic material and has a cylindrical wall and a base portion with a central opening for a primer. A set of peripherally situated heels (18) is attained by means of grooves extending from the end plane of the base portion, preferably a pair of concentric circular grooves (13, 14) and radial grooves (15) connecting the circular grooves, which grooves have a substantial extension in the axial direction of the case, preferably at least about 2/3 of the minimum axial material thickness of the base portion. These heels absorb the powder charge gas pressure and execute a translatory displacement in the axial direction of the case without the primer hole being deformed, whereby leakage of powder charge gases through the primer hole and displacement of the primer itself are avoided. In one embodiment, the primer opening is enlarged at its region connecting to the powder charge chamber and forms a cavity for receiving an adhesive means in the form of a collar adhered to the primer, thereby providing further insurance against displacement of the primer due to the powder charge gases.

Description: TITLE : Sh otgun cartr id ge case-sleeve and a cartri d ge ma d e t h ere- TECHNICAL FIELD: The invention relates to shotgun cartridge cases and to cartridges made therefrom. BACKGROUND OF THE INVENTION: Cartridges for shotgun-shooting have been the subject of heated discussions among hunters and shooters for the last century. Theories relating to cartridge action vary from time to time, as do opinions on how a cartridge case and the components therein should be constructed. Historically, the development has progressed from brass cases, cardboard/metal-base cases, plastic/metal-base cases to cases manufactured entirely from plastic. With few exceptions, cases of the latter type have, however, remained on the drawing board. The specific requirements for shotgun cartridge cases are particularly demanding. A utilisable case must be able to tolerate, for example, a gas pressure of up to 800 Bar. Its diameter should be such that it corresponds to nominal gun calibers +-0,1 - 0,5 mm. After firing, the case should be easy to remove using an extractor or, alternatively, an ejector. Leakage of powder gas should be minimal. The case should be adaptable to all types of shotgun, including semi-automatic shotguns . Naturally, the case must not rupture or leave residue in the gun, which could result in barrel rupture with catastrophic consequences. The base serves to form a shape-stable bottom with a seat for the primer. The base also forms the abutment plane against the gun's action body. The case sleeve, particularly its front portion, should create as tight a seal as possible against the bore of the barrel under the influence of the gas pressure from the powder charge and the case sleeve should furthermore be such that it can accommodate the required components, i. a. powder, wad and shot. The front portion of the case sleeve is advantageously such that it can be upset to thereby create a closure and hold the shot charge in place against the wad. As is indicated in the introduction, attempts have been made to manufacture shotgun cartridge cases entirely from plastic. It has been recognized that the material costs can thus be reduced and that manufacturing costs can also be lower since it allows for rational manufacturing methods. Furthermore, with regard to environmental and recycling aspects, there are advantages to be gained, particularly if it were possible to manufacture the shotgun cartridge case solely of a plastic material (mono-material). STATE OF THE ART: One method for manufacturing shotgun cartridge cases of plastic which has been used on occasion is based on manufacturing the various parts of the cartridge case of mutually separate plastic material. Thus, for the base, a stronger, i.e. more pressure-resilient, and more shape- permanent plastic material is selected than for the sleeve portion. One example of this is shown in PCT Application No. WO 86/05871. So-called sequential injection moulding is used in the manufacturing of the cartridge in which, in a first step, the sleeve portion is injected and, in connection thereto, in a second step the base portion is injected using a different plastic material than that of the sleeve portion. Furthermore, in this cartridge construction, the sleeve wall in the region of the charge and the primer is made so as to consist of two material layers which together provide a stable base. Another example of manufacturing the base in a separate step using a different plastic material than for the sleeve body is shown in DE OS 24 19 577. By a special design of the primer hole with three mutually different diameters, the intention here has been to reduce the risk of powder gas release through the primer hole and thereby to reduce the risk of displacement of the primer. An example of a case sleeve made from biaxially oriented plastic material in an attempt to reduce the material thickness is described in US Patent No. 5,121,693. The cartridge case in this example is provided with a traditional base made from metal. A shotgun cartridge case made in one piece from plastic is described in US Patent No. 3, 550 531. According to the disclosure of that patent, the base portion is designed to be able to optimally convert powder gas energy into propulsive energy for the shot charge and to prevent the case from rupturing. The shaping of the base with weakened waist portions between an internal groove and external recesses does, however, imply that there is a large risk of the primer hole expanding such that powder gas is forced out between the primer and the wall of its hole. The primer can be displaced from its position and make it impossible to break the gun after firing. SUMMARY OF THE INVENTION: It is therefore an object of the invention to provide a shotgun cartridge case made completely of plastic, and shotgun cartridges made therefrom, in which the cartridge case is made in one piece by injection moulding of a single plastic material (mono-material), and in which the base portion is shaped so that it meets current specification demands and functions at least as well as a traditional metal base. The object of the invention is achieved by a shotgun cartridge case and a shotgun cartridge having features in accordance with appended claims 1 and 13, respectively. Preferred further developments of the basic concept are detailed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS: The invention will be exemplified in the following with reference to the attached drawings, in which: Fig. 1 is a cross sectional view of a shotgun cartridge case according to a preferred embodiment, Fig. 2 shows the base portion of the case on a larger scale, Fig. 3 is a plan view of the base portion, Fig. 4 shows the case in Fig. 1 in a sealed and charged condition with its constituent components, Fig. 5 shows a shotgun cartridge case before its front portion is upset, Fig. 6 shows a shotgun cartridge with an arrangement for ensuring the location of the primer, Fig. 7 is a partial view showing the base portion with the primer hole according to the invention in one embodiment, Fig. 8 shows the base portion in a partial view with the primer hole and associated base parts in a modified embodiment, and Fig. 9 schematically shows the primer with associated adhesion-increasing means removed from the seat in the base of either of the embodiments in Figs. 7 and 8. The shotgun cartridge case shown in Fig. 1 is manufactured in one piece by injection moulding plastic material. In the present example, the material is HD-polyethylene. The injection moulding takes place in a multi-stage tool provided with means for core drawing or the like to make shaping as simple as possible. Measures have been taken in the mould to counteract shrinking of the plastic material, though at the same time this is done so that optimal material thicknesses can be used throughout in the final product. The material thicknesses in question are, for example, cartridge case sleeve about 1-2 mm, thickness of the base portion in the axial direction about 5-8 mm. The cartridge case comprises a sleeve having a cylindrical wall 10 and a base portion 11 having an opening 12 intended to receive a primer. The base portion 11 is provided with a pattern of grooves, i.e. an inner circular groove 13 around the primer hole 12 and a radially outer circular groove 14. Radial grooves 14 are connected to these circular grooves at peripherally equidistant distances. All of these grooves extend relatively deeply into the base portion from its end plane 16 and thus present considerable extensions in the axial direction of the cartridge case. The depth of the grooves in the preferred embodiments extend to at least 2/3 of the material thickness of the base portion 11, as represented by the distance between the dashed lines 16 and 17 in Fig. 1. Heels 18 are formed between the grooves 13, 14 and 15 and are located peripherally equidistant from each other in the base portion 11. The grooves 13, 14 in Fig. 1 have been shown as having the same depth, though it is also possible to provide the grooves with different depths so that the outer groove 14 extends somewhat further into the material in the base portion, to the level indicated by 19. A first circumferentially extending material portion 20 is situated between the inner circular groove 13 and the primer hole 12 and this material portion has a radial material thickness which is greater than the radial material thickness of a radially outer material portion 21 which is delimited by the outer groove 14. A seat 22 is formed in the end surface of the first material portion 20 for the rim of the primer. The hole 12 is dimensioned so that the primer can be fixedly held by the walls of the hole with a press fit. The radially outer material portion 21 terminates in an extractor rim 23. The material thickness in the radial direction of the circumferential material portion 20, as previously mentioned, is considerably thicker than the corresponding material thickness of the radially outer material portion 21. The purpose of the inner material portion 20 is to retain the primer in its proper place during the formation of powder gas and, for this purpose, the greatest possible radial material thickness should be used for the inner material portion 20. At the same time, the material thickness in the radial direction must not be too small for the outer circumferential material portion 21 since the extractor rim 23 must provide the necessary abutment strength for the gun's extractor after firing. Trials have shown that a ratio of at least 2 : 1 between the material thicknesses of the inner material portion and the outer material portion is desirable. A circular waist portion 25 of reduced material thickness remains between the heels 18 and the powder charge base 24 between the dashed lines 26, 27 (Fig. 2). As a result of the particular symmetrical placement of the heels 18 and the sizing of the material thickness of the waist 25, as well as the material thickness in the given manner of the inner material portion 20, preconditions have been attained for controlled absorption of the gas pressure with retention of the primer in its proper location in the hole 12. The placement and guiding of the heels, both during manufacturing and during use, are further aided by arranging material webs 28, 29, with an axial length somewhat shorter than the depth of the groove in the shown embodiment, radially in respective groups 13, 14 and made in one piece with both the heels and the material portions 20, 21. The purpose of these webs, which have considerably less material thickness in the peripheral direction than the heels 18, is to stiffen the base portion, though still permitting the heels to perform their intended function. As a result of said dimensioning and placement of the material portions, the grooves, the heels and the webs, as well as the stated material thickness dimensioning, the embodiment of the base portion of the shotgun cartridge case shown in Figs. 1-3 is particularly suited to tolerate the high gas pressure which arises during firing. The gas pressure follows the law of least resistance and since the circumferential waist 25 and the heels 18 formed in one piece therewith is the weakest region seen from the powder charge, this will give a translatory force acting axially towards the powder base 24 which elastically projects the heels 18 a short distance away from the bottom plane 16. The strain on the walls of the primer hole 12 will be minimal from this translatory force and the primer is maintained in its engagement position against the walls of the hole. The outer wall of the primer can also be provided with a suitable pattern of recesses, grooves or knurling. When the primer is being press-fitted into the primer hole, the plastic material is given the possibility to "flow out" and form a friction-increasing arrangement with the pattern of recesses. In certain cases, and as previously mentioned, it can be advantageous to make the outer groove 14 deeper. This can be particularly advantageous when the powder combustion chamber has the curvature as shown in the drawing, whereby the material thickness in the waist 25 becomes more uniform along its entire radial width. A shotgun cartridge case is shown in Fig. 4 according to the described embodiment in a loaded condition. In the shown example, a top closure has been attained by upsetting the sleeve end 30 shown in Fig. 5. The upset end is placed above the shot charge 31 which is accommodated in a bowl of a known type of wad 32 which is provided with a bottom bowl to define a powder chamber 33 between the wad and the base portion of the case. A primer 34 is located in the primer hole 20. Since the subject of the invention, including the primer, is a mass-produced product, every change to constituent standard components naturally implies an increase in costs of the end product. In certain applications, it is not justifiable to manufacture particular primers or subsequently machine standard primers, and thus there is a need for a more cost-effective solution to the problem of further securing the primer against displacement and leakage of powder gases. Examples of such solutions are shown in Figs. 6-9. In Fig. 6, a seat 22 for the rim of the primer is formed in the end surface of the base portion. The size of the hole 12 is such that the primer is insertable, preferably by a press fit in the hole 12. At the end of the primer hole 12 facing the powder chamber 33, a circumferential widening 35 is made, in the shown example in the form of an enlarge cylindrical portion of the primer hole 12 in the base portion. The extension in the axial direction for the enlarged cylindrical portion 35 is, in the embodiment, about half the length of the hole 12 which forms the opening for the primer 34. In Fig. 7, the arrangement of the widening 35 of the primer hole 12 is shown on a larger scale. The dashed lines 36 denote the extension of the hole 12 without the widening. Once a primer has been inserted, the widening 35 forms a distinct, well defined space in the base portion 11 between the outside of the primer and the delimiting side of the widening, i.e. concentric cylindrical sides defining a shaped cavity 37 in the shown example. The shaped cavity 37 is intended to accommodate means which provide adhesion at least to the outside of the primer 34. As is known, the primer is made from metal whilst the cartridge case is entirely manufactured from a monoplastic, for example HD-polyethylene. Means for achieving adhesion are present in many forms, including very flowing forms. Choice of suitable adhesion means/adhesive is made taking into account initially its ability to achieve binding with the primer of metal, whereby this binding should be as strong as possible. Certain adhesion to the plastic in the base portion is of course advantageous if this can be achieved. The purpose of the adhesion-creating means in the shaped cavity or the gap 37 is to provide the primer with a peripheral collar 38 as shown in Fig. 9. This collar 38 is attained by injecting a liquid binder into the shaped cavity or the gap 37 after application of the primer in a conventional manner in the base portion 11 so that the binder hardens and forms said collar 38. In order to attain the widening of the primer hole according to Fig. 7, the cylindrical primer hole 12 is suitably bored out to a depth corresponding to approximately half the material thickness, whereby the boring determines the delimiting wall of the widening 35. Alternatively, the special hole shaping can take place directly in connection with the injection moulding, though this demands further measures when removing the cartridge case from the mould. Since the means which create adhesion are preferably very fluid, a certain quantity of the means can seep into the region of the primer hole which is normally dimensioned to be a press fit against the primer. This can further improve the locating of the primer. Primarily, however, the locating will be achieved with the collar 38, i.e. increase with a radial width of the shaped cavity, whereby the adhesion of the collar 38 to the primer will also determine the locating or retaining capability. Even though only one type of widening for forming a collar has been shown, it will be realized that other shapes than the cylindrical shape are applicable even if, from a production point of view, cylindrical is presently optimal. The adhesive means can also be applied so that the collar 38 at the top of Fig. 9 is given a peripheral brim which entirely or partially is adhesively fastened to the bottom of the powder chamber and forms further reinforcement of the fastening of the primer. The described embodiments of the shotgun cartridge cases and cartridges are presently the most preferred, though it is to be realized that there are possibilities of variation of the groove pattern in the base portion, though the basic idea is that the grooves will provide a translatory displacement of weakened regions in the base portion without the position of the primer being affected. In addition, the energy which is consumed when executing the translatory displacement will favourably contribute to reducing the stresses in the transition region between the base portion and the cartridge case sleeve, thereby avoiding rupture. Even though mono-plastic material has been mentioned in the description, it is to be understood that it does not necessarily have to be a "pure plastic material". Instead, additions of fillers, for example chalk or the like, can be suitable if such material can otherwise fulfil the required demands .

Claims: CLAIMS : 1. Shotgun cartridge case comprising a body (10) having a cylindrical wall and a base portion (11) with a central opening (12) intended for a primer, whereby the body and the base portion are made as an integrated unit from injection-mouldable plastic material, c h a r a c t e r i z e d i n that a pattern of grooves (13, 14, 15) with substantial extension in the axial direction of the case is provided extending from the end plane (16) of the base portion, and in that said grooves together form partial regions, for example heels (18), which are axially displaceable by the powder charge gases. 2. Shotgun cartridge case according to claim 1, c h a r a c t e r i z e d i n that said grooves comprise an inner circular groove (13) which, together with the primer hole (12), define a radially inner material portion (20), and an outer circular groove (14) which defines a radially outer material portion (21) which terminates radially outwardly in an extractor rim (23). 3. Shotgun cartridge case according to claim 2, c h a r a c t e r i z e d i n that said grooves also comprise radially extending grooves (15) between said inner and outer grooves, which radially extending grooves (15) are preferably equidistant, whereby each partial region or heel (18) is formed by a pair of adjacent radial grooves (15) and said inner- and outer grooves (13, 14). 4. Shotgun cartridge case according to claim 3, c h a r a c t e r i z e d i n that each partial region or heel (18) is connected to said inner- and outer material portions (20, 21) by means of a radially inner (29) and a radially outer (28) web arranged in respective circular grooves and with considerably less material thickness in the peripheral direction than the peripheral material thickness of the partial region or heel. 5. Shotgun cartridge case according to claim 4, c h a r a c t e r i z e d i n that the axial end surfaces for the said both peripheral material portions (20, 21) and the axial end surfaces for the partial regions or heels (18) are substantially planer and all lie in the same radial plane. 6. Shotgun cartridge case according to any one of the preceding claims, c h a r a c t e r i z e d i n that the depth of the grooves in the base portion (11) is at least about 2/3 of the base portion's minimum axial material thickness. 7. Shotgun cartridge case according to claim 6, c h a r a c t e r i z e d i n that the inner wall of the base portion (11) connects to the inner wall of the cartridge sleeve in a transition wall region which has a varying wall thickness, such that a conically tapering charge combustion chamber is attained in the direction of the primer opening. 8. Shotgun cartridge case according to any one of the preceding claims, c h a r a c t e r i z e d i n that the radially inner material portion (20) has a considerably greater radial material thickness than the radially outer material portion (21), preferably at least twice as large. 9. Shotgun cartridge case according to claim 8, c h a r a c t e r i z e d i n that the peripheral outer circular groove (14) in the base portion has a greater depth than the inner groove so that an imaginary line connecting the bases of the grooves has a curvature corresponding essentially to the base of the powder charge combustion chamber for facilitating the displacement of the partial regions or the heels due to the powder charge gases. 10. Shotgun cartridge case according to claim 1, c h a r a c t e r i z e d i n that said central opening (12) in the base portion has a widening (35) at its inwardly facing end. 11. Shotgun cartridge case according to claim 10, c h a r a c t e r i z e d i n that the widening forms an enlarged cylindrical portion (35) of the hole (12) in the base portion which forms the primer opening. 12. Shotgun cartridge case according to claim 10 or 11, c h a r a c t e r i z e d i n that the widening has an extension corresponding to about one half the length of the hole. 13. Shotgun cartridge comprising a case (10) having a cylindrical wall and a base portion (11) with a central opening intended for a primer (34), wherein the cartridge comprises an end closure (30) and a wad arrangement (32) which, together with the end closure, defines a chamber (31) for accommodating shot, and, together with the base portion, defines a chamber (33) comprising a powder charge adjacent the primer, said body and base portion being made as an integrated unit from injection moulded plastic material, c h a r a c t e r i z e d i n that a pattern of grooves (13, 14, 15) with substantial extension in the axial direction of the case are provided extending from the end plane of the base portion, and in that said grooves define partial regions or heels (18) which are displaceable axially by the powder charge gases. 14. Shotgun cartridge according to claim 13, c h a r a c t e r i z e d i n that its primer is provided on its walls adjacent the walls of the primer hole with a pattern of recesses, grooves or the like. 15. Shotgun cartridge according to claim 13, c h a r a c t e r i z e d i n that said central opening (12) in the base portion has a widening (35) at the end which faces within the case, and in that said widening accommodates means (35) having adhesive properties at least with respect to the primer. 16. Shotgun cartridge according to claim 15, c h a r a c t e r i z e d i n that the widening forms an enlarged cylindrical portion (37) of the opening in the base portion which forms the primer hole. 17. Shotgun cartridge according to claim 15 or 16, c h a r a c t e r i z e d i n that the widening has an extension of about one half the length of the hole.

Inventors: JOHANSSON KONNY, KARLSSON ROLAND, JOHANSSON, KONNY, KARLSSON, ROLAND
Applicants: JOHANSSON KONNY, KARLSSON ROLAND, TOMSCOT HB, JOHANSSON, KONNY, KARLSSON, ROLAND
Application year: 1998
Main classification: F42B7
IPC codes: F42B5