For armour piercing projectiles a general rule is that a heavy core is desirable, this being the active part of the projectile by impact in a target. It is aimed at making the non-active mass, the parasitic mass, as small as possible. The ideal would be that the projectile merely consisted of the core and a charge, but this does not lead to an optimum solution for full calibre ammunition. This can be explained as follows.

The penetration capability of a projectile is related to the kinetic energy by impact against a target, and which is determined by the formula E = 1/2 m v2. However, the penetration capability also is a function of the core diameter, and more precisely it is inversely proportional to the core diameter. The following empirical formula has been derived for determination of the penetration capability: <BR> <BR> <BR> <BR> <BR> <BR> <BR> Cmv<BR> <BR> <BR> <BR> <BR> <BR> T =<BR> D where C is a constant determined by the type of target and the shape of the core, m is the mass of the core, v is the impact velocity and D is the diameter of the core. A presupposition for the formula is that the shape and internal integrity of the core is maintained during the penetration. The formula shows that as small core diameter as possible theoretically is the most favourable. In practice, when the core must have a large mass, this will lead to a long and thin core, which will collapse by impact without penetrating. Nevertheless, it will be favourable that the core has a smaller diameter than the projectile as a whole, i. e. that the core is subcalibrated. What is aimed at is that a largest possible amount of the projectile mass is to be constituted by the core.

A subcalibre core necessitates a lining around the core, and as such lining is among else used a plastics jacket. Thereby, also a charge, usually an incendiary charge, may be situated in front of the core inside of the jacket. In the core is used a heavy and hard material, for instance tungsten, tungsten carbide or hardened, alloyed steel. The use of a plastics jacket is, however, limited to small calibre projectiles, as the plastics jacket will not withstand the strains of propulsing itself and the remainder of the projectile in rotation

in the barrel of the weapon. Rotation is achieved in that the jacket is deformed into the rifles in the barrel, whereby the jacket is forced to rotate during the launching.

Simultaneously, the jacket causes sealing for the propulsive gases. Such deformation means a weakening of the plastics jacket. Moreover, a plastics jacket is unfavourable because it results in that the projectile has a small mass adjacent the periphery. This reduces the stability of the projectile in the trajectory. Pure plastics materials, therefore, have only been used for light projectiles, i. e. without a heavy core.

In practice ammunition for simulating shooting with armour piercing ammunition have been used cores of lead, having approximately the same weight and weight distribution as the core of hard metal, and the core may be surrounded by a jacket having the same external shape as the corresponding armour piercing ammunition. However, lead is a heavy metal which is undesirable to spread in the nature. For practice ammunition it is also substantial that it may be manufactured at low costs. As regards use, the practice ammunition should have approximately the same trajectory as armour piercing ammunition up to a certain distance, for instance 300-400 meters, but the maximum range should be smaller, for instance the half. Moreover, it is desirable that practice ammunition ruptures into fragments by inclined impact against targets, in order to avoid ricochets.

A jacket has not been used for armour piercing projectiles of larger calibre of more than about 15 mm, because the jacket, like plastics jackets for small calibre ammunition, will not withstand the strains of propulsing itself and the remainder of the projectile in rotation in the barrel of the weapon. It must be taken into consideration the enormous acceleration, also angular acceleration, which the launching entails. (For instance up to about 100000 G in linear acceleration). Therefore, guide bands of metal or plastics have been used, mounted in a circumferential groove in the projectile, in order to cause sealing for the propulsive gases and rotation, in that the guide band is deformed into the rifles in the barrel. As metal in such guide bands alloyed copper, soft steel and galvanized steel have been used.

As it will appear, a common aim for all these projectiles is to achieve that the core constitutes as large amount as possible of the mass of the projectile. This may be achieved by using a plastics jacket which is light and cheap, but such a jacket has shown to involve severe strength limitations. Moreover, the mass of the projectile adjacent the periphery is small, due to the low density of the plastics material.

An object of the present invention is to solve the problems related to the use of plastics jackets for projectiles which are to be driven in rotation in weapon barrels.

Thus, the invention relates to a projectile which contains a heavy core surrounded by a jacket, and is characterized in that the jacket is of plastics and is formed by two parts, with a circumferential partition, that a metal band is mounted about the partition between the jacket parts, and that the jacket parts are glued to the core. The metal ring is mounted in connection with the joining of the jacket parts. Each jacket part has a step on the end which is to be joined to the other jacket part, whereby the steps together form a circumferential groove in which the metal ring will be situated when the jacket parts are connected.

The jacket parts are glued to the core, in order to be kept on the core, and in order to be able to move the core; i. e. to impart angular acceleration to the core, during the launching.

The metal band causes rotation of the projectile in the barrel of the weapon and causes sealing for the propulsion gases during the launching. The metal band can be made of tombac.

During the launching. the metal band is pressed radially due to the rifles in the barrel, and the pressing increases the fixing of the metal ring against the jacket and secures transmission of torque thereto. Moreover, the metal ting is favourable in that it increases the mass of the jacket around the circumference and thereby improves the stability of the projectile in the trajectory.

The principle can be used for all the projectile types mentioned above. When the projectile is armour piercing, incendiary charge may be placed in front of the core inside the jacket. For practice ammunition a core of hard metal, for instance tungsten or tungsten carbide, may be used, but the core may be lighter than for armour piercing ammunition. In order to achieve that the core is fragmentized during an inclined impact, whereby ricochets are avoided, the core may be weakened by recesses or incisions, in order to burst in the impact.

For all embodiments the jacket, including the metal band, will be cheaper to manufacture than a continuous metal jacket.

For projectiles of larger calibre, for instance in excess of 15 mm, the fixing of the metal ring with respect to transfer of torque can be secured by mounting of the jacket parts mutually spaced and by pressing the metal ring into a groove in the core. Optionally, the groove may be formed with a pattern of flutes which prevent mutual rotation of the metal ring and the core.

When the core has weakenings in the form of circumferential grooves, rings can be mounted in the grooves in order to take up the pressure during launching. The rings must fill up the grooves axially. The rings have no influence with respect to the tensile strain which occurs in the core in an inclined impact, and do not prevent that the core bursts into fragments.

In the following examples of embodiments of the invention will be described, with reference to the accompanying drawings. Equal or equivalent parts have been given the same reference numerals.

Fig. 1 shows a longitudinal section through an armour piercing projectile according to the invention.

Fig. 2 shows a longitudinal section through a practice projectile according to the invention.

Fig. 3 shows a segment of a projectile according to the invention, with a metal ring pressed into the core..

Fig. 4 shows a segment of a core included in the projectile according to the invention, with a ring inserted in a weakening groove in the core.

The Figs. 1 and 2 will be described as a whole. The Figs. show projectiles having a heavy core surrounded by a jacket of plastics, formed by a front part 1 and a rear part 2.

The jacket parts 1,2 are glued to the core 4. A metal ring 3 is mounted in a circumferential groove formed at the transition between the jacket parts 1 and 2. The jacket parts 1 and 2 are shown mutually spaced. Thereby, tolerances with respect to the length of the metal parts 1 and 2 are avoided.

Fig. 1 shows an armour piercing projectile, and the core 4 is of hard metal and is rounded on the front end. Alternatively the core 4 may be more or less pointed. As material may as example be used tungsten, tungsten carbide or alloyed, hardened steel.

The chamber 6 in the nose portion of the projectile may be filled with an incendiary charge.

The practice projectile shown in Fig. 2 contains a core 4, which does not need to be of hard metal, as the purpose is to impart the desired ballistic properties to the projectile.

The core 4 is shown having blunt ends, as it shall not have any penetrating effect in a target. In order that the core shall not ricochet undivided by inclined impact against a target surface, the core 4 has weakening grooves 5, which will cause that the core will fragmentize by impact.

In particular for larger calibre projectiles it may be favourable, or necessary, to attach the metal ring 3 also to the core 4, and not only to the jacket. Fig. 3 shows how this can be achieved. The metal ring 3 has an inner, circumferential rib, and upon mounting of the metal ring 3 about the jacket parts 1 and 2 the metal ring 3 is compressed such that the rib protrudes into a circumferential groove in the core 4. The groove may have flutes in the axial direction of the projectile, whereby the metal ring 3 cannot rotate relatively to the core 4. Thereby, a large torque can be transmitted from the metal ring 3 to the core 4.

When the core 4 has weakening grooves 5, as shown in Fig. 4, bursting of the core 4 due to the strain at the launching can be prevented, in that a ring 7 is mounted in the groove or in each groove 5. The ring 7 transfers compressive strain through the groove 5.

The metal ring 3 is mounted in connection with the mounting of the jacket parts 1 and 2 on the core 4, in that the metal ring 3 is moved axially onto the jacket part 1 prior to mounting of the jacket part 2.

By launching in a rifled weapon barrel the metal ring 3 is pressed against the jacket part 2 because the metal ring 3 is deformed by the rifles.