SHELL FOR GUN WITH SMOOTH-BORE BARREL

Abstract: The present invention relates to a method for converting mortar shells (1) for use as non-rotating, fin-stabilized shells in guns with unrifled barrels. According to the invention, the warhead (14) of the original mortar shell is supplemented with a guide casing or discarding sabot (6, 17), adapted to the new barrel, and is provided with a tail fin (12, 15) without internal propellant charge, together with a conventional propellant powder charge for the gun in question. The finished shell is also included in the invention.

Description: Shell for gun with smooth-bore barrel The present invention relates to a method for converting certain mortar ammunition for use as fin- stabilized, non-rotating shells in smooth-bore guns, in particular tank guns. The invention also includes ammunition which has been converted in accordance with this method. The invention thus includes, on the one hand, a method for converting mortar shells for use as fin- stabilized, non-rotating shells in smooth-bore gun barrels, in particular tank guns, of essentially the same calibre as the mortars for which the shells in question were originally intended, and, on the other hand, a method for converting mortar shells, of smaller calibre than the gun barrels in question, to subcalibre non- rotating shells provided with discarding sabots, where the discarding sabots are separated in a known manner from the shells outside the muzzle of the gun barrel. The invention is considered to be of great value since there is plenty of mortar ammunition in stockpiles, and the high-explosive mortar shells in particular have well-designed shell bodies with good fragmentation properties, and at the same time there is some need for high-explosive shells for the tank divisions, who generally have artillery pieces with smooth-bore barrels. Of course, the invention also includes the converted shells and the complete rounds of which these form part. According to the invention, the actual conversion is carried out in such a way that the warhead of the original shell is kept unchanged, while its original tail fin, with internal propellant charge chamber, is either replaced by a new tail fin adapted to the new and higher velocity of exit (Vo) of the projectile, or is merely deprived of its internal propellant charge, at the same time as which the warhead is always provided with a guide part or guide casing which is adapted to the calibre gauge of the smooth-bore barrel in question and which is preferably provided with a bourrelet of the type regularly used as a powder gas seal in barrels of the type in question here. In purely general terms, the ordinary tail fin of the mortar shell is usually secured on the warhead by means of a screw thread. Particularly in those cases where the tail fin is to be replaced by a new one, the said screw thread can be used for securing the guide casing on the warhead, while the guide casing is in turn provided with a screw thread for the screwing-on of the tail fin. Moreover, the shells converted in accordance with the present invention are always intended to be supplemented with the propellant powder charge which is appropriate for the gun in question and which, in the case of tank guns, generally involves fixed propellant charges, and with which they can be combined to form complete rounds. The invention further includes two alternative possibilities for converting the mortar shell for use in smooth-bore barrels. The first variant is based on mortar shells intended for mortars of the same, or essentially the same, calibre as the smooth-bore guns in which the converted shells are intended to be used, and in this case the guide casing is mainly in the form of a casing which encloses and supports the rear part of the warhead of the original shell, the inside of which casing is shaped matching the outer shape of the warhead in order to increase the strength of the warhead against the firing stresses, and the rear portion of which casing is designed to be relatively strong, and the front portion of which casing consists of an approximately tubular and relatively thin-walled portion which adjoins the outer periphery of the warhead in the vicinity of its maximum diameter. In the more solid rear portion of the guide casing, there is also a bourrelet groove which is provided with a conventional bourrelet. The second variant of the invention is based on a mortar shell of smaller diameter than the gun barrel in question, and this shell is provided with a guide casing designed in accordance with the principles applying to discarding sabots for subcalibre projectiles, i.e. it is designed in three or more parts in the longitudinal direction, these parts being held together by means of locking bands which are intended to be torn off by the effect of the ram pressure when the projectile leaves the barrel. As in the first variant of the invention, the guide casing/discarding sabot in question here is also given a relatively strong rear portion, with an inner shape adapted to the outer shape of the warhead in order to increase the strength of the warhead against the firing stresses, and with associated guide grooves for a conventional bourrelet, and a more thin-walled front portion which expediently opens out in a cup shape at the front in order to offer a good point of attack for the relative wind. The method and the arrangement according to the invention, and the finished round which is obtained in accordance therewith, are defined in the attached patent claims and will now be described in somewhat greater detail in connection with the attached figures. Fig. 1 shows a side view of the starting point, namely a conventional high-explosive mortar shell, and Fig. 2 shows a partially cut-away side view of the converted high-explosive shell adapted for use in unrifled gun barrels. Fig. 3 shows a partially cut-away side view of a converted subcalibre-type shell provided with discarding sabot. The mortar shell 1 shown in Fig. 1 comprises a front warhead 2 (also seen in Fig. 2) and a rear tail fin 3 with inner propellant charge. The shell 4 shown in Fig. 2, and modified for use in unrifled barrels, comprises the explosive-filled warhead 2, while the tail fin 3 has been disassembled and its assembly screw thread 5 has been used for screwing-on of the guide casing 6. The latter has a relatively thin- walled, tubular front part 7, which encloses the rearwardly narrowing rear part 2a of the warhead 2, and a rear part on which a new tail fin 12 is firmly screwed, the said tail fin 12 being adapted to the new and higher velocity of exit (Vo) of the converted shell. The finished shell also includes a fuse 13, which can be the original mortar fuse or a newly constructed mortar fuse. Fig. 3 shows the second variant of the shell according to the invention. In this case the starting point is a shell 14 of smaller calibre than the barrel in question, and here the original tail fin 15 has been retained, but deprived of its original internal prop¬ ellant charge. The fuse 16 has also been retained in its original form. In contrast, the shell has been supple¬ mented with a discarding sabot (guide casing) 17 a-c, which is divided in three parts in the longitudinal direction and is held together by connection rings 18 and 19 and also the bourrelet 20. These come to be torn off by the ram pressure when the shell leaves the barrel muzzle, after which the discarding sabot parts leave the shell in a known manner, with the shell continuing its trajectory alone. The three parts 17 a-c of the discar¬ ding sabot are designed in such a way that the latter has a relatively solid rear and central portion 21, which fits closely against, and supports, those parts of the original shell body which, upon firing, are exposed to the greatest stresses, while its front portion 22 is relatively thin-walled and opens out in a cup shape at the front around the forward part of the shell body 14, in order to give the ram pressure a good point of attack there. The shells which are converted according to the invention are always supplemented with a conventional propellant powder charge for the artillery piece in question.

Claims: PATENT CIAT-MS 1. Method for converting mortar ammunition for use as fin-stabilized shells in preferably smooth-bore gun barrels, characterized in that the warhead (2) of the original shell is kept unchanged, but is supplemented with a guide casing (6, 17) which is adapted to the smooth-bore barrel and which adjoins at least the rear part of the warhead (14) and supports the latter, and with an associated bourrelet (9, 20) adapted for sealing against the inside of the barrel, while the propellant charge incorporated in the tail fin (3, 15) of the original shell is replaced with a conventional propellant charge for the gun in question. 2. Method according to Claim 1, characterized in that the original tail fin (3) of the shell, with its internal propellant charge chamber, is replaced by a tail fin (12) which is adapted for the new and higher velocity of exit (Vo) of the converted shell. 3. Method according to Claim 2, characterized in that the tail fin (3) of the original shell is disassembled from the warhead (2) , and the screw thread (5) on which this tail fin was originally secured is used for mounting of the rear guide casing (6) , while the new tail fin is in turn screwed securely around a rear cylinder (11) projecting from the guide casing (6) . 4. Method according to Claim 1, characterized in that the guide casing (17a-c) is designed as a multi-part discarding sabot which is adapted for subcalibre projectiles and which, at the level of the barrel muzzle, is separated, by means of the ram pressure, from the warhead, chosen with a smaller calibre than the barrel, and its associated tail fin (15) . 5. Fin-stabilized, non-rotating shell intended for smooth-bore guns and converted from a mortar shell (1) in accordance with the method according to one or more of Claims 1 or 4, characterized in that it comprises, firstly, the warhead (2, 14) of the mortar shell, i.e. its active charge and associated housing, secondly, a tail fin (12, 15) without internal propellant charge, and, thirdly, a guide part (6, 17) whose outside is adapted to the calibre gauge of the gun barrel, and whose inside has at least in part been adapted to bear against the rear part of the warhead. 6. Fin-stabilized, non-rotating shell intended for smooth-bore guns in accordance with Claim 5, characterized in that its guide part (6, 17) adapted to the gun barrel in question has the form of a guide casing (7) , which encloses at least the rearwardly narrowing rear part of the original mortar shell, and a bourrelet (8, 21) running about the outer periphery and adapted to the calibre gauge of the barrel. 7. Fin-stabilized, non-rotating shell intended for smooth-bore guns in accordance with either of Claims 5 or 6, characterized in that the guide part (guide casing) (6) of the shell is secured on the threaded cylinder (5) which has originally held the original tail fin (3) of the mortar shell, while the said guide part itself has its own threaded part (11) on which the tail fin (12) of the converted shell is screwed. 8. Fin-stabilized, non-rotating shell intended for smooth-bore guns in accordance with either one of Claims 5-7, characterized in that the guide casing (6) has a solid rear part (8, 21) provided with a bourrelet (9) which is adapted to the calibre gauge of the artillery piece in question, and a thin part in the form of a collar (7) of essentially unchanging external diameter which, at the front, adjoins the forward part of the warhead, and whose frontmost part has been adapted to the external diameter of the warhead (2) at the point, along its length, where they adjoin one another. 9. Fin-stabilized, non-rotating shell intended for smooth-bore guns in accordance with Claim 5, characterized in that its guide casing has the form of a multi-part discarding sabot (17a-c) which is adapted for subcalibre projectiles and which is designed in such a way that, upon firing, it is separated, at the level of the barrel muzzle, from the warhead (14) , chosen with a smaller calibre than the barrel, and its associated tail fin (15) . 10. Fin-stabilized, non-rotating shell intended for smooth-bore ' guns in accordance with Claim 9, characterized in that, in addition to its rear part (21) which is adapted to the warhead, the guide casing (17a-c) also has a part (22) which opens out in a cup shape at the front, in the direction of firing, and which extends along at least part of the front part of the warhead and forms, between its own inner side and the said front part of the warhead, a forwardly directed open space. 11. Complete round for a smooth-bore gun, in particular a tank gun, characterized in that it includes a shell modified from a mortar shell (2, 14) in accordance with any one of Claims 5 - 10, and a conventional propellant charge for the gun in question.

Inventors: FREDRIKSSON LENNART, WIKSTROEM ARNE, FREDRIKSSON, LENNART, WIKSTROEM, ARNE
Applicants: BOFORS LIAB AB, FREDRIKSSON LENNART, WIKSTROEM ARNE, FREDRIKSSON, LENNART, WIKSTROEM, ARNE
Application year: 1995
Main classification: F42B30
IPC codes: F42B14, F42B30