ARMOUR PENETRATING PROJECTILE

This invention relates to a high precision armour piercing projectile for light arms.

Background

Personnel in anti-terror units, special task forces in both police and army, may encounter situations that require putting out specific targets in narrow and sometimes also fortified positions from a long distance. Examples of such situations may be passivating a hostage taker hiding in a building/vehicle, military sniper missions etc.

Such situations requires light fire arms and ammunition which delivers a projectile at extreme precision over long distances in combination with a high penetration capability and a very good directional stability during/after penetration solid objects standing in-between the shooter and target.

Prior art

There are known many different projectiles for small arms that are made armour piercing by inserting a dense and hard core, such as a cylindrical object of a heavy metal. Most of these are however encumbered with a relatively complicated design including a mantle layer, soft matrix material, usually lead, and an embedded armour penetrating core which make them relatively costly in production. It is also questionable if these projectiles will be sufficiently directional stable through and after penetration of an in-between standing solid barrier, since they contain a soft matrix material that will deform upon impact with the barrier material. Examples of such solutions are disclosed in US 4,895,077, US 4,633,782, US 4,384,528, US 4,108,073, FR 2,771,496 Al, and DE 41 39 598 Al.

The problem of obtaining extreme precision for small arms ammunition is more or less solved by manufacturers of hunting ammunition for rifles. The requirements for weight distribution spin and bullet design for giving the projectiles an optimum precise trajectory are well known to a person skilled in the art, and need no further presentation. Hunting ammunition is however, designed to deform upon impact on the target. Thus they will in general have a poor armour penetrating ability, and they will suffer from a poor directional stability if they need to pass through a solid barrier in-between the shooter and target.

Object of the invention

The main object of this invention is to provide a projectile that combines excellent precisions and excellent penetration capability in solid materials without being excessively deformed and without being unsatisfactory deflected of course.

A second objective of this invention is to provide a simple, cost-effective and versatile manufacturing method for producing projectiles according to the invention.

The objectives of the invention may be obtained by a projectile that has the features as defined in the claims and/or the following description of the invention.

List of figures

Figure 1 shows a preferred embodiment of the invention based on the bullet design presented in Swedish Design Registration No. 69721.

Summary of the invention

The inventive idea is to employ the bullet design of conventional high-precision ammunition made of yellow metal, bore a hole from the tip and downwards along the centre axis of the projectile until a short distance above the base of the projectile, and then insert a dense and hard cylindrical object which is somewhat longer and have a somewhat larger diameter than the bore hole. Thus the central cylindrical insert will be held firmly in place and protrude a distance in front of the yellow metal body of the projectile, and therefore function as the projectiles first point of contact and the main transmitter of the projectiles kinetic energy to the target.

One advantage of the projectile according to the invention is that is has a simple construction made up of only two metal components, a body of yellow metal and cylindrical rod-shaped insert made of an armour penetrating material. The term "yellow metal" means a body of brass, copper, bronze or gilding metal. All of the mentioned metals may be used as the body material of the projectile. The term armour penetrating material means any material, metal, alloy, composite or other solid material that has a density, Young's modulus and sufficiently high melting point to function as an armour penetrating object. Thus any material known to be armour penetrating to a person skilled in the art may be employed as the cylindrical insert in this invention.

The design of the body of the projectiles is not essential as long as the design shows high-precision capability, preferably at muzzle velocities up to 1250 m/s. Thus, any high precision bullet design known to a person skilled in the art may be implemented into the body of the projectile according to this invention.

The annular distal end (front end) of the protruding cylindrical insert should preferably be sharp in order to provide a good gripping ability of the projectile when hitting a surface at other angles other than perpendicularly onto the target surface (90°). The length of the protrusion, that is the length of the part of the cylindrical insert protruding out of the projectiles body, should be sufficiently long to allow the front end of the insert to be the first point of contact at hitting angles up to at least 45°.

From the point of view of obtaining a maximum flight stability, the length of the cylindrical insert embedded into the projectiles body should be as long as possible

in order to obtain a density distribution along the projectile's centre axis as homogeneous as possible. Thus the insert should run all the way through the body down to the base in order to obtain a maximum flight and impact stability. However, from a mechanical strength and penetration point of view, the cylindrical insert should have a sufficiently thick base of the projectiles body to avoid that the insert loosen and penetrating the base of the projectile's body upon firing or contact with the target. This will be detrimental to the projectiles armour penetrating and directional stability through a solid target, since in this case, it will be the relatively ductile body material of the projectile that becomes the first point of contact and transmitter of kinetic energy of the projectile to the target. Thus there is a trade off between the need for avoiding destabilising the flight trajectory (maintain high- precision trajectories) and the need for giving the base a sufficient thickness to avoid penetration by the insert. It has been found that the thickness of the base, that is the distance from the bottom of the bore to the base, should preferably be in the range of from 1/2 to 1/30, more preferably from 1/3 to 1/10, more preferably from 1/4 to 1/6, and most preferably about 1/5 of the longitudinal length of the projectile.

The projectile according to the invention may have any calibre, or outer diameter, ranging from saloon rifles to heavy military fire arms. The diameter of the centre insert should be in relation to the calibre of the projectile. A ratio diameter of insert over total diameter of projectile of about 1/4 has shown to function very well for projectiles with calibre .308 (7.62 mm), or a centre cylinder of about 2 mm diameter. However there is no known reason why other diameter should not function, such that the inventive idea should not be limited to this diameter ratio of 1/4. It is envisioned that different needs and bullet designs may allow any conceivable diameter ratio ranging from about 1/12 to about 2/3.

The simple construction of only two metal components of the projectile according to the invention gives a great benefit in that the body of the projectile may be turned out from a solid rod of yellow metal in for example a CNC (computer numerical controlled) lathe. Thus most of the complicated productions steps with a filler metal in-between a hard core and jacket, which in general is case with conventional armour penetrating bullets, are avoided. The use of a CNC-lathe is a very versatile and cost-efficient production method that allows customising the design of individual bullets/projectiles to meet different user demands, without need of making new and very costly dies as in the conventional production methods.

The excellent armour penetration capacity of projectiles according to the invention, a body of ductile yellow metal with a protruding rod of armour penetrating material, is highly unexpected for a person skilled in the art since the yellow metal body is known to provide excellent deformability properties making the material suited for use in hunting ammunition where the projectile should attain a mushroom shape upon entering an animal body. It is also unexpected that high precision bullet designs maintain their excellent precision when equipped with a protruding insert

with a sharp annular front end. Nor is it obvious that a soft bodied projectile will be suited for high precision targeting through an in-between lying solid obstacle such as a window, wall, metallic sheet, brick wall, armour plate etc.

Detailed description of the invention

The invention will be described in more detail under reference to preferred embodiments of the invention. However, these embodiments should not be interpreted as a limitation of the general inventive idea of providing a yellow metal body a protruding insert of an armour penetrating material.

In general it is preferred to employ a bullet design with a flat base, no boattail, for projectiles intended to be fired at short ranges and at moderate wind conditions. A preferred bullet design for such applications is presented in SE design registration 69721, belonging to the present inventor. This design is preferred since this bullet design has commercial success and has proven to form premium high-precision bullets at muzzle velocities up to 1100 m/s. In the same manner, the inventor's bullet design as given in SE design registration 69722 is preferred for projectiles intended to be used at longer distances or in windy conditions.

Both designs registrations are incorporated into this application by reference.

Preferred embodiment of the invention

Figure 1 shows a schematic drawing of a preferred embodiment of the invention intended for military use. In the drawing, numeral 1 refers to a body of yellow metal which is given a similar bullet design as in SE design registration 69721, numeral 2 refers to a bore into the body 1 running from the tip 3 towards the base 4 along the centre axis. An armour penetrating insert 6 is placed into the bore 2 in such a way that it protrudes a distance above the tip 3 of the body 2.

The body 2 is made of electrolytic copper. The calibre is .308 (7.62 mm outer diameter of the body), and the body is equipped with an interface area 8 comprising nine driving bands that bears against the inside of the barrel as firing is commenced. The length of the engaged area is 14 mm. The driving bands give the projectile several advantages over conventional designs without such bands: less bullet friction down the barrel and thus less heat generation from the passage of the bullet, less contamination of the inside of the barrel by material of the projectile, and thus less build up of friction due to deposits from the projectiles, less barrel vibrations trough the firing sequence, and less friction means increased muzzle velocity, usually of about 15-30 m/s depending on the calibre and bullet type.

Another specific feature of this bullet design is that at the cross section where the last driving band meets the ogival, a bore rider that is a cylindrical portion for 2mm

length is positioned. This is a unique feature because it lets the bands right in front of the chamber rest against the borerider portion of the bullet, such that a precise alignment of the bullet partly in the bore is assured. Thus the possibility of ruining ^" the precision is eliminated. Also, in accordance with the CIP and SAAMI standard accredited in the gun industry of today, the bullets according to the invention are custom tailored such that the bore rider sections are touching what is the land diameter on a CIP and SAAMI standard diameter rifle. This is believed to be the single most important reason to why the projectiles according to the invention outperform conventional bullets in accuracy tests.

Preferably both the first belt behind the bore rider and the last belt at the base of the bullet are twice as broad as the other belts. Thus the front belt will have sufficient material for the lands to grab the bullet and sustain the rotational movement without spinning to much on the lands as the bullet starts moving into the barrel. This is especially a problem on the heavy calibre projectiles. The rear bands sole purpose is to make an effective gas seal against the bore avoiding the very warm (2000 to 2200 °C) and high pressure gasses (340 to 380 MPa) start leaking past the bullet base.

The armour penetrating insert 6 in the preferred embodiment of the invention, should preferably have a diameter of two mm and reach down to about six mm above the base 4 of the projectile body 2. The annular edge 7 of the insert 6 should be sharp and protrude about 0.4 mm above the tip 3 of the body 2, in order to obtain a good gripping and penetration capability at impact angles up to 45°. The preferred material of the insert 6 is tungsten carbide, since it has a very high melting point of about 287O ⁰ C, a density of 15.8 g/cm ³ , and a Young's modulus of about 620-720 GPa.

As most military cartridges is held inside stringent standards for ballistic coefficient and weight of projectile, the preferred embodiment for military applications is without a boattail in order to keep the weight at 155 grain, 10.0 g. However for long distance shooting, the tungsten core would enhance the ballistics of a long sleek bullet with a Very Low Drag boat tail and a slightly extended ogival with a radius of about R-60.

Method of production.

It is preferred to manufacture the preferred embodiment of the invention by turning out the body from a rod of yellow metal in a CNC-lathe since this method is cheap and gives the excellent tolerance and repeatability that is required for high precision projectiles. Another advantage with use of a CNC-lathe is that it is easy to customise the design of the projectile according to a wide range of intended appliances. CNC production is commonly used and well known to a skilled person, such that there is no need to go into programming details.

There are two tolerances on the body of the projectile that is important in order to obtain the intended high-precision performance; the outside diameter engaging the lands in the bore and the dept and diameter of the hole holding the tungsten core. The acceptance criteria is +/- 0,01mm on the OD of the bullet. The driving band bullet is a very forgiving bullet design when it comes to shooting bullets with lager than standard diameter.

The projectiles made for verification of the invention is produced on a Goodway 150 SLC, a 3 axis CNC with power driven drilling from the turret. The capacity of the machine in respect to tolerances on the finished product is normally 0.005mm which is satisfactory for any type of bullet.

It is preferred to employ any of electrolytic copper, brass, bronze, or telleur copper as raw material for the projectiles body. The especially preferred and mostly used' material is copper followed by brass. The material is delivered in 5 to 6 m long bars 8, 10, 12, and 14 mm depending on the calibre being produced. Our opinion is that copper both gives the best properties for internal ballistics, meaning the barrels is easy to keep free of copper fouling and it also gives less barrel wear than the harder and more brittle alloys as brass and bronze but these alloys gives a slightly higher muzzle velocity with the same power charge all other parameters being equal.

Copper is also the chosen alloy because it is more ductile and less brittle than brass therefore it transfers all the kinetic energy to the tungsten core much better than the brass bullets that has a tendency to disintegrate on impact against metal targets causing less energy transfer to the tungsten core.

Verification of the invention.

In order to verify the precision and penetration abilities of the invention, there is performed test shootings with the preferred embodiment of the projectile as specified above (body of electrolytic copper, calibre .308 or 7,62 mm diameter, insert of tungsten carbide protruding 0.4 mm in front of the body, bullet design according to Swedish design application SE 69721, and weight 10. Og).

The first series of tests was aimed at verifying the necessary penetration capability. For these tests there was used 308 Norma Magnum rifle that gave the projectile according to the preferred embodiment specified above a muzzle velocity of approx. 970 m/s. The projectiles were fired against a 25 mm thick steel plate (grade ST 42) at 90° angle from a distance of 25 m. All projectiles managed to penetrate the plate, showing that a penetration ability of at least 25 mm steel is established.

The second series of tests was aimed at verifying the precision of the preferred embodiment of the projectile. For these tests there was employed a Tikka T3 Varmint Stainless steel with Leupold scope 6,5 -20 x 40, and the bullets were loaded with 42,5 and 43,5 gr Norma 11 powder. The cartridge length was 71.6mm. RR cases with Remington 91/2 large rifle primers. This gave the projectiles a

muzzle velocity of 840 m/s. The projectiles were fired at a distance of 97 meters against a soft target (cardboard sheet) in two series of three shots. The two groups showed a spread centre to centre of maximum of 7 mm and 10 mm, respectively. This corresponds to approx. 0,25 and 0,50 MOA (minute of angle), which is an exceptional good precision.

The third series of tests was aimed at verifying the stability of the flight trajectory when passing a solid obstacle. These tests were performed with the same equipment and set up as the second series of tests above (the precision test), with the exception that a plate of laminated glass of 8 mm thickness was placed between the shooter and target in a distance 2 m from the target. The target was a coloured square of 15x15 mm on the cardboard sheet. First the laminated glass plate was placed such that the projectile will hit with a 90° angle, and there was fired one shot. Now the hit point was approx. 8 mm from the precise centre of the target, showing that the projectile obtained an insignificant deviation in the flight path when passing through the glass plate at a perpendicular angle. Then the test were repeated with the laminated glass plate inclined such that the projectile would hit the glass plate at an angle of 45°. This time it was fired two shots, which hit the target at 15 and 17 mm from the precise centre of the target, respectively. Thus, when passing a solid in-between standing solid object at the highest intended hit angle of 45°, the projectiles flight trajectory was deviated less than 0.5°. This is a deviation well within acceptable limits.

Thus the preferred embodiment of the invention is verified as a high precision projectile with excellent penetration abilities.