GB2299155A

GB2299155A - Discarding sabot projectiles

Info

Publication number: GB2299155A
Application number: GB8712008A
Authority: GB
Inventors: Bernhard Bisping; Hans-Joachim Kaltmann; Ulrich Theis; Siegfried Kessler
Original assignee: Rheinmetall Industrie AG
Current assignee: Rheinmetall Industrie AG
Priority date: 1986-05-21
Filing date: 1987-05-21
Publication date: 1996-09-25
Anticipated expiration: 2007-05-21
Also published as: SE8702034D0; GB8708674D0; FR2730050A1; GB2299155B; GB8712008D0; DE3716609C1; IT8747959A0; FR2730050B1

Abstract

A discarding sabot projectile system has a metal propulsion base 40 provided with a sleeve-shaped receiver 60 having longitudinally axial slits 64 as preset breaking points, and a plastic shroud 80 connected to the propellant base 40 by screw threads 74, 97. Longitudinal axial recesses 90, 92 reduce the mass and the recesses 90 function as preset breaking points. Between a front internal surface zone 68 of the sleeve-shaped receiver 60 and a smooth peripheral surface zone 14 of the projectile 10, frictional contact prevails.

Description

TITLE Discarding Sabot Proiectiles The invention relates to a discarding sabot projectile.

A sabot projectile is known from Swiss Patent 5 36 481. The sub-calibre projectile, made of a material of considerable density, has two peripheral grooves and terminates in a frustum-shaped zone forming a common edge with the tail surface. A supporting surface in the propellant base of the projectile is funnel-shaped and adapted to the frustum-shaped zone at the tail of the projectile, the crosspieces of the receiver are situated inside with the exception of a narrow zone reserved for an annular groove and all rest internally against the peripheral surface of the projectile. To enable the projectile to be fixed in the axial direction by an interlocking principle each crosspiece is pressed from the outside into each of the two peripheral grooves.

The slits between the crosspieces of the receiver only extend as far as a circularly cylindrical zone which rests tightly against the projectile and which is immediately followed at the rear by the funnel-shaped supporting surface. The recesses provided in the centering casing and having the effect of reducing the wall thickness are delimited in the front and at the rear in the longitudinal direction. The insertion aid forms a separate part to be connected with the front portion of the centering casing. At the rear the centering casing is designed, on a level with the part in which it is connected to the propellant base, to form a tightening and guide band.

For attack on manoeuverable and at least partly armoured targets, such as attack helicopters and ground vehicles, a projectile is required which is of a high density of its material (at least 17g/cm-3 as known from DE 29 19 897), and is so brittle that with very thin target skins of a light metal alloy it initially disintegrates into the maximum possible number of highenergy splinters effective both over a surface and in depth. In other words, this means that the projectile can only be subjected to very limited tensile stress, as great a part of it as possible being made of the material in question. Further indispensable demands made on the projectile are rigidity when being fed into position and inserted and maximum firing rate and rigidity under extreme pressure.

If the sabot projecile described previously is considered solely from the point of view of the aforementioned requirements as regards the material and its suitability in this connection, considerable problems arise in the method of fixing the projectile in the axial direction in the propellant base: the very limited tensile strength precludes the provision of peripheral grooves in view of the required insertion and firing rigidity; apart from this and in addition to the costintensive manufacturing process they detract from the final ballistic performance, as a high c coefficient in w which the result leads to a noticeable decrease in velocity. In addition the interlocking connection is cumbersome and expensive and has to be equally counterbalanced over the entire periphery of the projectile at all relevant points, in order not to impede the latter.It is likewise liable to be impeded, however, even after the crosspieces of the receiver have broken away as a result of twist, by the interaction between the cylindrical zone in front of the funnelshaped supporting surface in the propellant base and the tail zone of the projectile which is tightly embraced thereby under considerable pressure. The recesses in the centering casing, which are delimited in the front and at the rear, involve axial and radial movements to enable parts of an injection mould to be detached from the finished workpiece. They also suffer from the disadvantage of causing uncontrolled disintegration of the centering casing in front of the barrel mouth.An additional disadvantage is the fact that the hood-shaped insertion aid forms a special component and a snap fastening between the insertion aid and the centering casing, a connection which calls for expensive operations on both these parts, can be released by hand and may thus give rise to faulty operations when the aforementioned type of fastening does not offer adequate protection against atmospheric influences such as the ingress of moisture. A final fact which must be regarded as a drawback is that the centering casing in its rear zone has to perform simultaneously a number of functions which subject it to extreme stresses.

It may be seen from the foregoing details that the very dense and also extraordinarily brittle material from which the projectile is produced makes almost contradictory demands. For the firmness required in the insertion and firing operations concern not only the projectile itself but also the propellant base and its receiver, the connection between the said base and the centering casing and also the load which the latter is capable of bearing and which is determined by its supporting cross section.

An object of this invention is to provide a sabot projectile for a sub-calibre multi-purpose fragmentation projectile of dense and brittle material, which will be simple to manufacture and which will fulfil the aforementioned requirements.

According to this invention there is provided a discarding sabot projectile system having a metallic propulsion base provided in the front part with a sleeveshaped receiver having longitudinally axial slits as preset breaking points leaving cross pieces and with a plastic centering casing interlockingly connected with the propellant base and having longitudinally axial recesses in each case reducing the wall thickness in order to reduce the mass and functioning as preset breaking points, and with a hood-shaped insertion aid of plastic connected in the front to the centering casing and terminating at a point in the front via a recessed peripheral surface and serving for a sub-calibre projectile designed for twist stabilization and to be fixed in the system until it leaves the rifled barrel of a gun and made of a plastic material with a density of at least 17 g/cm 3, and also with a guide tightening band and at least one twist groove serving for connection with a propellant charge casing, characterized by the following features: (a) the centering casing and the insertion aid form a unit; (b) between a front internal surface zone of the sleeve shaped receiver for the projectile, on the front side of the propellant base, and a smooth peripheral surface zone of the projectile, frictional contact prevails, while by internal surface zones of the centering casing and of the insertion aid respectively the projectile in its circularly cylindrical part and in the zone of a point is tightly embraced and axially centered; (c) the interlocking connection between the propellant base and the unit extends over a conical zone and has the known characteristics of a traction screw connection; ; (d) the recess extends the whole way from a rear zone to the zone of the point of the insertion aid and terminates in that position; (e) the slits extend as far as a flat front supporting surface for the tail surface of the projectile and terminate in a peripheral groove, a radial gap being left between the peripheral surface of the projectile in the tail zone and the internal surface adjacent to the supporting surface; (f) in order to ensure the maximum wall thickness for the centering casing immediately in front of the connection zone between the centering casing and the propellant base, the receiver is given the minimum possible wall thickness in the frictional contact zone;; (g) between a circular line externally associated with a transition from the centering casing to the insertion aid and an internal circular line, in the firing direction S, an axial gap is left which corresponds to between 0.25 and 0.5 of the diameter of the projectile, while an angle associated with the external circular line and left between the track of the peripheral surface of the centering casing and the track of the adjacent peripheral surface of the insertion aid amounts to between 28 and 35e, and (h) the guide and tightening band are each positioned, with an axial gap, between the rear boundary of the unit and a twist groove on the propellant base.

The invention is explained below in greater detail by reference to a preferred embodiment shown in the drawing as example.

In the drawings: Figure 1 shows a sabot projectile in accordance with the invention, shown in longitudinal axial section along a line I-I of Figure 2, Figure 2 shows a plan view thereof on a smaller scale and in the direction indicated by the arrow II of Figure 1, Figure 3a shows a longitudinal axial section through a receiver with first interlocking closure means positioned in an external zone, shown as an enlarged detail drawing, and Figure 3b shows a detail drawing showing a longitudinal section through the rear zone of a centering casing with second interlocking closure means positioned internally.

According to Figure 1 a projectile 10 of extremely brittle material has a density of at least 17g/cm-3, a circularly cylindrical part 12 has a smooth peripheral surface 14 and a front edge 16 in common with the peripheral surface 20 of nose zone 18. A rear edge 26 delimits a conical tail part 28 with a peripheral surface 30 and a tail surface 32. A propellant base 40 of a metallic material of low density and high strength has a rear recess 42 with a boundary surface 44 and a central axial detonation boring 46 for a tracer composition (not shown) in the tail part 28 of the projectile 10. In the peripheral zone 48, at an axial distance apart and behind an offset portion 56, a guide and tightening band 50 and at least one twist groove 52 are provided for the purpose of connecting the sabot projectile with a propellant casing not shown in the drawing.In front of the offset part 56 a circular annular groove 58 is provided which is delimited in the front by a plane 61 belonging to a supporting surface 62 level therewith. The latter rests on the front side 54 of the propellant base 50 and forms the rear termination of a sleeve-shaped receiver for the projectile 10. Slits 64 which continue at the rear as far as the plane 61 evenly subdivide the receiver 60 into crosspieces 66 with a front boundary 76. The internal surface of the receiver 60 is subdivided into a front circularly cylindrical zone 68 immediately followed at the rear by a funnel-shaped zone 70 merging into the supporting surface 62.On the outside the receiver 60 is provided with a conical zone 72 delimited at the rear by the circularly annular groove 58 and containing first interlocking closure means 74 in the form of a conical threading or grooves passing the whole way round. They serve to provide the connection with a unit 80 made of a plastic material and consisting of a rear centering casing 82 and an insertion aid 84, which connects up in a transition 86 and is provided with a point 85. An external surface 88, which is in the main of circularly cylindrical shape, is interrupted by recesses 90 which reduce the wall thickness, take a longitudinal direction and serve to form preset breaking points, and recesses 92 serving to reduce the mass (by reducing the dead weight part of the sabot projectile).

The longer recesses 50 extend from a rear zone 54 open as far as the point 85 of the insertion aid 84. The recesses 92 are shorter but likewise terminate open in the front. The unit 80 is delimited at the rear by a circularly annular surface 96. A funnel-shaped internal surface zone 95 belonging to the unit 80 and adapted to the conical zone 72 of the receiver 60 is provided with second interlocking closure means 97 corresponding to the first closure means 74. The funnel-shaped internal surface zone 95 is immediately followed in the front by a circularly cylindrical internal surface zone 98 of the centering casing 82. An internal circular edge 104 forms the transition to the funnel-shaped internal surface zone 100 of the insertion aid 84.A circular line 102 associated with the transition 86 from the outer surface 88 of the centering casing 82 to the outer surface 89 of the insertion aid 84 precedes the circular edge 104 as viewed in the direction shown by an arrow S (direction of firing) at an axial distance 106 (approximately corresponding to 0.25 to 0.5 times the diameter 22 of the projectile 10). This ensures a front zone 107 with an optimum supporting cross-section. A transition angle 108 amounts to between about 28 and 35c and not only ensures unimpeded operation under extreme conditions but also a further reduction in the dead weight proportion of the sabot projectile.

The injection moulded unit 80 in the example shown in Figure 1 is provided with interlocking closure means 97 such as can be seen in Figure 3b. They may consist of an internal threading corresponding to the closure means 74 (Figure 3a) of the receiver 60 which in this case takes the form of external threading. The aim is to avoid notch effects by radii r as as far as possible and at the same time enable the force to be evenly transmitted throughout the entire connection zone 120 by the conicity of this latter and also to give the projections 75 and 97 equal bearing capacity by heights h, widths b and angles > t and A The foregoing description illustrates the advantageously simple and thus economical manufacture of the sabot projectile according to the invention.

The results obtained when the system was tested were as follows: accelerations transverse to the longitudinal axis A of the projectile, such as occur when it is being fed into position, when the ammunition belt in the ammunition box is suddenly pulled, on the way from that position to the belt feed device and in this latter as well as a phase of the change of direction occurring in the insertion process, cause no damage even when occurring at the highest rate of firing frequency.The achievement of this object is assisted not only by the construction of the said centering casing 82 and the insertion aid 84 as a unit 80 and the construction of the zone 107 (larger supporting cross section being provided by the axial gap 106) but also by the fact that the projectile 10 is supported without play and over most of its length and by the connection between the unit 80 and the propellant base 40. Both the considerable transition angle 108 and the recesses 82 and space 71 offer the advantage of reducing the dead weight part of the sabot projectile. The axial accelerations acompanying the insertion operation likewise have no disadvantageous results. this too is partly achieved by means of the construction of the zone 107. A further considerable contribution to this result, however, is made by the reciprocal (and at the same time centering) supporting action in the zone of the surfaces 20 and 100), the friction contact between the surfaces 14 and 68 in the relevant zone, the ample supporting cross section in the zone 99, the mechanical and constructional characteristics of the conical form-closure connection zone 120 and the resulting interaction with the properties of the material in the unit 80 and the propellant base 40. The firmness obtained in the firing action is likewise due to the individual characteristics adopted for this purpose and also to the interaction between them.In conjunction with the firmness in the insertion process mention should also be made of the nature of the twist connection between the sabot projectile and the propellant charge casing, although this does not form the subject of the present invention.

It must in all cases be borne in mind, however, that the material of the projectile 10 is characterized not only by an extremely high density but also by exceptional brittleness.

The trial also indicated the following method of operation: after the projectile leaves the drawn barrel the preset breaking points 90 become operative under the twist effect. This leads to four separate fragments of largely equal size and thus calculable as regards their range and consistency of departure from the projectile flight traject. It has been proved that they do not form any impediment for the projectile. The friction contact between the projectile 10 and the propellant base 40 is immediately nullified as a result of the fact that the crosspieces 66 rapidly and simultaneously move over outwards, this action being assisted by the circular annular groove 58 operating as a preset breaking point.

Together with the friction contact, however, any contact between the propellant base 40 and the projectile 10 is likewise nullified; the circular annular part belonging to the flat supporting surface 62 and forming the bottom limit for the space 71 having a diameter which is greater than the diameter 22 of the projectile 10 ensures such a high cw coefficient for the remainder of the propellant base that this latter, immediately after passing through the mouth of the barrel is already at a considerable distance from the projectile, which it therefore cannot impede; its non-oscillatory further movement in the direction shown by the arrow S is thus reliably ensured.

As the guide and tightening band 50 is situated on the propellant base 40 at an axial distance behind the rear boundary 96 of the unit 80, this latter is kept free, in a zone in which the wall thickness is critical, from deformation by the fields and rifling of the barrel and also from any stresses caused by hot propellant gases subject to high pressure.

Particular importance attaches to the construction of the connection zone 120. The very different properties of the materials concerned, i.e. that of the propellant base 40 and that of the unit 80, are a decisive factor.

Where screw connections are concerned the following values are mentioned for guidance; the length of the connection zone 120 is between 0.8 and 0.2 times the diameter 22 of the projectile 10. In the middle (at half the height) of the tooth of the threading in each case the width of that made of the same plastic material as the unit 80 is greater by at least a factor of two than the width of that made of the same light metal alloy as the propellant base 40. The depth of the threading (transversal extensions; height h) should be as moderate as possible, this being the only way of ensuring the maximum obtainable wall thickness with the corresponding supporting cross section in the zone 99. It amounts to between about 0.05 and 0. 1 times the diameter 22 of the projectile 10, thus meeting the demands made on it.

Although the conditions required in the connection zone 120 can be ensured in a particularly reliable manner by means of threading, ultrasonic welding has also proved satisfactory. The grooves passing round the outer peripheral zone of the receiver 60 are subject to similar conditions to those which have been described with the threading.

Claims

1. A discarding sabot projectile system having a metallic propulsion base provided in the front part with a sleeve-shaped receiver having longitudinally axial slits as preset breaking points leaving.cross pieces and with a plastic centering casing interlockingly connected with the propellant base and having longitudinally axial recesses in each case reducing the wall thickness in order to reduce the mass and functioning as preset breaking points, and with a hood-shaped insertion aid of plastic connected in the front to the centering casing and terminating at a point in the front via a recessed peripheral surface and serving for a sub-calibre projectile designed for twist stabilization and to be fixed in the system until it leaves the rifled barrel of a gun and made of a plastic material with a density of at least 17 g/cm -3, and also with a guide tightening band and at least one twist groove serving for connection with a propellant charge casing, characterized by the following features:: (a) the centering casing and the insertion aid form a unit; (b) between a front internal surface zone of the sleeve shaped receiver for the projectile, on the front side of the propellant base, and a smooth peripheral surface zone of the projectile, frictional contact prevails, while by internal surface zones of the centering casing and of the insertion aid respectively the projectile in its circularly cylindrical part and in the zone of a point is tightly embraced and axially centered; (c) the interlocking connection between the propellant base and the unit extends over a conical zone and has the known characteristics of a traction screw connection; (d) the recess extends the whole way from a rear zone to the zone of the point of the insertion aid and terminates in that position;; (e) the slits extend as far as a flat front supporting surface for the tail surface of the projectile and terminate in a peripheral groove, a radial gap being left between the peripheral surface of the projectile in the tail zone and the internal surface adjacent to the supporting surface; (f) in order to ensure the maximum wall thickness for the centering casing immediately in front of the connection zone between the centering casing and the propellant base, the receiver is given the minimum possible wall thickness in the frictional contact zone;; (g) between a circular line externally associated with a transition from the centering casing to the insertion aid and an internal circular line, in the firing direction S, an axial gap is left which corresponds to between 0.25 and 0.5 of the diameter of the projectile, while an angle associated with the external circular line and left between the track of the peripheral surface of the centering casing and the track of the adjacent peripheral surface of the insertion aid amounts to between 28C and 35", and (h) the guide and tightening band are each positioned, with an axial gap, between the rear boundary of the unit and a twist groove on the propellant base.

2. A sabot projectile in accordance with Claim 1, characterized by the following features; (a) the length of a connection zone associated with the interlocking connection amounts to between 0.8 and

1.2 times the diameter of the projectile; (b) the width of the individual interlocking element in the plastic of the unit is in its radial centre (at half the height h) at least twice as great as the width of the adjacent interlocking element of the propellant base; and (c) the transversal extension h of the connection zone amounts to between 0.05 and 0. 1 times the diameter of the projectile.

3. A projectile in accordance with Claim 1 or 2, characterized by a screw connection associated with the connection zone.

4. A projectile in accordance with Claim 1 or 2, characterized by a connection by means of ultrasonic welding between the propellant base and the unit.

5. A projectile as described herein and exemplified with reference to the drawings.

5. A projectile in accordance with one of Claims 1 to 4, characterized by the fact that the recesses are interconnected crosswise.

6. A projectile as described herein and exemplified with reference to the drawings.

Amendments to the claims have been tued as tOlIOWS CLAIMS 1. A discarding sabot projectile unit having a metal propulsion base provided with a cup-shaped receiver for a spin stabilised projectile having a density of at least 17g.cm-3, the receiver having longitudinal side pieces defined by slits forming preset breaking points, a plastic shroud enclosing the projectile and receiver and connected with the propulsion base and having longitudinal recesses reducing the wall thickness and thus the mass and forming preset breaking points, the unit having a guide and sealing band and at least one groove serving for connection with a propellant charge casing, characterised by frictional engagement being provided between internal surfaces of the side pieces of the cup-shaped receiver and a peripheral surface zone of the projectile, the shroud tightly embracing and axially centering both a cylindrical body portion and a nose portion of the projectile, the connection zone between the propulsion base and the shroud being conical, the longitudinal recesses in the shroud extending from a rear zone to the nose of the projectile, the slits in the cup-shaped receiver extending to meet a flat front support surface for the tail of the projectile and terminating in an annular groove, a circumferential gap being provided between the tail zone peripheral surface of the projectile and the internal surface of the receiver adjacent to the said front support surface, the transition between the cylindrical body portion of the projectile and a nose part thereof being longitudinally and rearwardly displaced from a transition between a tapering forward surface of the shroud, forming a loading guide, and a rear cylindrical surface thereof, by a distance corresponding to 0.25 to 0.5 of the projectile diameter, the angle between the rear cylindrical surface of the shroud and the tapering forward surface thereof being between 280 and 35O, and the guide and sealing band being positioned on the propulsion base periphery forwardly of the propellant charge casing groove.

2. A sabot projectile unit in accordance with Claim 1, characterised by an interlocking connection between the propulsion base and the shroud, the length of the zone of the interlocking connection being between 0.8 and 1.2 times the diameter of the projectile, the width of an interlocking element on the shroud at the half height point being at least twice the width of the complementary interlocking element on the propulsion base, and the height h of the interlocking element being between 0.05 and 0. 1 times the diameter of the projectile.

3. A projectile in accordance with Claim 1 or 2, characterised by the connection comprising screwthreading.

4. A projectile in accordance with Claim 1, characterised by the connection betueen~the propulsion base and the shroud comprising an ultrasonic ueld.