Shotgun cartridge case-sleeve and a cartridge made therefrom

Shotgun cartridge cases are disclosed which are produced from a unitary body of plastic material. The shotgun cartridge cases include a cylindrical wall with a based portion which includes a central opening adapted to receive a primer, and a number of grooves extending axially from the end plane of the cartridge case and defining displaceable regions of the base portion whereby these displaceable regions are axially displaceable by means of powder charge gases released by the cartridge. Shotgun cartridges are also disclosed.

FIELD OF THE INVENTION
 The present 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 of cartridge cases has progressed from brass
 cases, cardboard/metal-base cases, and 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 of .+-.0.1 to 0.5 mm. After firing, the cartridge
 case should be easy to remove using an extractor or an ejector. Leakage of
 powder gas should be minimal. The case should be adaptable to all types of
 shotguns, 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 of the cartridge case 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 also 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 noted above, 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).
 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 materials. Thus, for the base,
 a stronger, i.e. more pressure-resilient, and more shape-permanent plastic
 material is selected than that used for the sleeve portion.
 One example of this is shown in PCT Application No. WO 86/05871. So-called
 sequential injection molding 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 that used for the sleeve body is shown in
 German Application No. 2,419,577. 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 to thereby
 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 U.S. Pat.
 No. 5,121,693. The cartridge case in this example is provided with a
 traditional base made from metal.
 In U.S. Pat. No. 3,760,729 there is disclosed a glass fiber reinforced
 plastic cartridge case. The case is explicitly designed to have a rigid
 base. There is a groove extending from the end plane of the base portion
 of the case.
 The reasons for having the groove (the term used in the specification of
 said patent is "coring") are as follows:
 1. to avoid uneven cooling and sinking of the molded case;
 2. to avoid long molding cycles required by cooling of the thick base; and
 3. to avoid physical weakness at the juncture of the thick base with the
 thin wall of the case. (See col. 4, lines 1-6).
 The plastic cartridge case disclosed in U.S. Pat. No. 3,088,405 is also
 designed to have a rigid base in the embodiments shown in FIGS. 7,9, and
 11, and the base of the cartridge is reinforced by a plurality of ribs. In
 col. 3, starting on line 49 it is stated: "by said ribs 38, tubular
 section 34 with counter pocket (probably means "primer pocket") 35 is
 interconnected with the wall of case 31 whereby a firm, rigid structure is
 provided having adequate support for the primer . . . ".
 A shotgun cartridge case made in one piece from plastic is described in
 U.S. Pat. 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.
 It is therefore an object of the present 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
 molding 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.
 SUMMARY OF THE INVENTION
 In accordance with the present invention, these and other objects have now
 been realized by the invention of a shotgun cartridge case comprising a
 unitary body of plastic material including a cylindrical wall having an
 outer surface and an inner surface and a base portion defining an end
 plane and having an inner wall, the base portion including a central
 opening adapted to receive a primer, and a plurality of grooves extending
 axially from the end plane and defining a plurality of displaceable
 regions of the base portion, whereby the displaceable regions of the base
 portion are axially displaceable by means of powder charge gases released
 by the cartridge. Preferably, the plurality of grooves extend through a
 substantial portion of the base portion.
 In accordance with one embodiment of the shotgun cartridge case of the
 present invention, the plurality of grooves includes a first groove
 comprising an inner circular groove proximate to the central opening
 thereby defining an inner material portion of the base portion between the
 first groove and the central opening and a second groove comprising an
 outer circular groove distal to the central opening thereby defining an
 outer material portion of the base portion between the second groove and
 the outer surface of the cylindrical wall. Preferably, the shotgun
 cartridge case includes an extractor rim extending radially outwardly from
 the outer material portion adjacent to the end plane.
 In accordance with one embodiment of the shotgun cartridge case of the
 present invention, the case includes a plurality of third grooves
 extending radially within the base portion between the first groove and
 the second groove. In a preferred embodiment, the plurality of third
 grooves are equidistantly spaced from each other, whereby each of the
 plurality of displaceable regions of the base portion is formed by a pair
 of the third grooves, the first groove and the second groove.
 In accordance with another embodiment of the shotgun cartridge case of the
 present invention, the case includes a plurality of radial inner webs and
 a plurality of radial outer webs, each of the plurality of displaceable
 regions being connected to the inner material portion and the outer
 material portion by at least one of the plurality of radial inner webs and
 at least one of the plurality of radial outer webs. In a preferred
 embodiment, the plurality of radial inner webs and the plurality of radial
 outer webs has a first thickness and the plurality of displaceable regions
 has a second thickness, the first thickness being substantially less than
 the second thickness. Preferably, the outer material portion and the inner
 material portion include an axial end surface, and the plurality of
 displaceable regions include axial end surfaces, and the axial end
 surfaces of the outer material portion, the inner material portion, and
 the plurality of displaceable regions are substantially planar and lie in
 a common radial plane.
 In accordance with another embodiment of the shotgun cartridge case of the
 present invention, the base portion includes a maximum axial thickness and
 the plurality of grooves extend through the base portion a distance at
 least about two-thirds of the maximum axial thickness. In a preferred
 embodiment, the case includes a transition wall region connecting the
 inner wall of the base portion to the inner wall of the cylindrical wall,
 the transition wall region having a varying wall thickness whereby a
 conically tapering charge combustion chamber is provided facing the
 central opening.
 In accordance with another embodiment of the shotgun cartridge case of the
 present invention, the inner material portion has a first radial thickness
 and the outer material portion has a second radial thickness, the first
 radial thickness being substantially greater than the second material
 thickness. In a preferred embodiment, the first radial thickness is at
 least two times the second radial thickness.
 In accordance with another embodiment of the shotgun cartridge case of the
 present invention, the first groove has a first depth defining a first
 base wall and the second groove has a second depth defining a second base
 wall, the second depth being greater than the first depth whereby a line
 connecting the first base wall to the second base wall has a curvature
 substantially corresponding to the inner wall of the base portion, whereby
 the axial displacement of the plurality of displaceable regions is
 facilitated.
 In accordance with another embodiment of the shotgun cartridge case of the
 present invention, the central opening in the base portion includes a
 first portion adjacent to the end plane having a first width and a second
 portion adjacent to the inner wall of the base portion having a second
 width, the second width being greater than the first width. In a preferred
 embodiment, the second width of the central opening defines an enlarged
 cylindrical surface in the central opening.
 In accordance with another embodiment of the shotgun cartridge case of the
 present invention, the first portion of the central opening and the second
 portion of the central opening have substantially the same axial length.
 In accordance with the present invention, a shotgun cartridge has also been
 invented comprising a unitary body of plastic material including a
 cylindrical wall having an outer surface, an inner surface, a first end
 and a second end, and a base portion at the first end of the cylindrical
 wall defining an end plane and having an inner wall, the base portion
 including a central opening adapted to receive a primer, the cartridge
 including an end closure at the second end of the cylindrical wall, a wad
 member disposed within the cartridge and spaced from the end closure and
 the base portion whereby the space between the end closure and the wad
 member is adapted to receive shot means and the space between the wad
 member and the base portion is adapted to receive a powder charge, and a
 plurality of grooves extending axially from the end plane and defining a
 plurality of displaceable regions of the base portion, whereby the
 plurality of displaceable regions of the base portion are axially
 displaceable by means of the powder charge gases released by the
 cartridge.
 In accordance with a preferred embodiment of the shotgun cartridge of the
 present invention, the cartridge includes the primer disposed in the
 central opening, the primer including an outer surface for contacting the
 inner surface of the central opening, the outer surface of the primer
 including a pattern of recessed means.
 In accordance with another embodiment of the shotgun cartridge of the
 present invention, the central opening in the base portion includes a
 first portion adjacent to the end plane having a first width and a second
 portion adjacent to the inner wall of the base portion having a second
 width, the second width being greater than the first width. Preferably,
 the cartridge includes adhesive means disposed within the second portion
 of the central opening for adhering the primer to the central opening. In
 a preferred embodiment, the second width of the central opening defines an
 enlarged cylindrical surface in the central opening.
 In accordance with another embodiment of the shotgun cartridge of the
 present invention, the first portion of the central opening and the second
 portion of the central opening have substantially the same axial length.

DETAILED DESCRIPTION
 The shotgun cartridge case shown in FIG. 1 is manufactured in one piece by
 the injection molding of plastic material. In a preferred embodiment, the
 material is HD-polyethylene. The injection molding takes place in a
 multi-stage tool which is provided with means for core drawing or the like
 in order to make shaping as simple as possible. Measures have been taken
 in the mold to counteract shrinking of the plastic material, though at the
 same time this is done so that optimal material thicknesses can be used
 throughout the final product. The material thicknesses in question are,
 for example, cartridge case sleeve with about 1 to 2 mm thickness and the
 base portion in the axial direction being about 5 to 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 15 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 a preferred embodiment extends 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 and 14, in FIG. 1 have been shown as having the same depth,
 though it is also possible to provide the grooves with different depths,
 as shown in FIG. 10, 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 about 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
 and 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 and 29, with
 an axial length somewhat shorter than the depth of the groove in the shown
 embodiment, radially in respective groups, 13 and 14, and made in one
 piece with both the heels and the material portions, 20 and 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 this 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 provide 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 will be 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 enabled 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
 above-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 present invention, including the primer, is a
 mass-produced product, every change to constituent standard components
 naturally implies an increase in the cost of the end product. In certain
 applications, it is not justifiable to manufacture particular primers or
 subsequently machine standard primers, and there is thus 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, there is provided a circumferential widening 35, in
 the example in the form of an enlarged 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 this 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, while the cartridge case is entirely manufactured from
 a monoplastic, for example HD-polyethylene. Means for achieving adhesion
 are present in many forms, including flowing forms. The choice of a
 suitable adhesion means/adhesive is made by initially taking into account
 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 the
 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 molding, though this demands further measures when removing the
 cartridge case from the mold.
 Since the means which create adhesion are preferably very fluid, a certain
 quantity of this 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 locating of the primer.
 Primarily, however, 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 is entirely or partially
 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
 hereof 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 favorably
 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.
 Although the invention herein has been described with reference to
 particular embodiments, it is to be understood that these embodiments are
 merely illustrative of the principles and applications of the present
 invention. It is therefore to be understood that numerous modifications
 may be made to the illustrative embodiments and that other arrangements
 may be devised without departing from the spirit and scope of the present
 invention as defined by the appended claims.