During the First World War, the belligerents began to use personal armor protection for infantrymen in the form of steel helmets and cuirasses, which at a certain distance could not be penetrated by low-velocity small arms bullets. At the moment, SIBZ with composite plates of boron carbide with a thickness of 9 mm cannot be penetrated by armor-piercing bullets with a steel core of calibers 5, 45x39 mm, 5, 56x45 mm, 7, 62x39 mm, 7, 62x51 mm and 7, 62x54 mm at a distance of less than 100 meters …
To overcome this obstacle, armor-piercing bullets of small arms are increasingly using a core made of a composite alloy of tungsten carbide with cobalt of the VK8 type with a grain size of less than 1 μm, the ultimate strength of which in bending is 2 GPa, in compression of 4 GPa at hardness HRA 85 units. Even more promising is a metal alloy of tungsten of the VNZh97 type, by analogy with the cores of armor-piercing artillery shells. However, the SIBZ plates also have a reserve for increasing durability both by increasing the percentage of boron carbide in the composite and by the thickness of the plates (taking into account the tendency to switch to the use of passive exoskeletons as part of infantry equipment).
In addition, the classic ogival shell bullet is an extremely ineffective carrier of the armor-piercing core, since it requires the use of a lead jacket to pass through the rifling of the barrel without destroying them upon contact with the hard alloy of the core. As a result, the mass of the core itself is reduced to a minimum. For example, a bullet of a cartridge 7N24M of caliber 5, 45x39 mm with a bimetallic jacket, a lead jacket and an armor-piercing core made of VK8 alloy weighs 4.1 grams, of which the weight of the core is only 1.8 grams. In addition, when colliding with the SIBZ plate, part of the kinetic energy of the bullet is spent on crushing the bimetallic shell, piercing it with an armor-piercing core and tearing off the lead jacket.
A more effective method of increasing the armor penetration of small arms bullets is to increase their initial velocity and reduce the cross-sectional area. The first measure increases the kinetic energy of the bullet, the second increases the specific load in the contact patch of the bullet with the obstacle. The bullet speed is limited by the maximum pressure of the powder gases in the barrel, which currently reaches 4500 atmospheres and is determined by the strength of the barrel steel. This limitation is overcome by reducing the mass and diameter of the bullet while maintaining the same bore diameter - i.e. by switching to sub-caliber bullets. To guide a sub-caliber bullet in the barrel bore, developed leading belts on the surface of the core or a polymer pallet are used, the density of the material of which is 9-11 times less than the density of brass or lead.
The first constructive solution in this area is the bullet of the German Harold Gerlich, developed in the first third of the 20th century and equipped with two leading conical belts. The bullet in flight was stabilized by rotation, the rifled barrel had a variable diameter, tapering towards the end, which made it possible to achieve even greater efficiency in using the energy of the powder gases. As a result, a bullet weighing 6.5 grams accelerated to a speed of 1600 m / s and pierced a steel plate 12 mm thick at a distance of 60 mm. However, a rifled barrel of variable diameter was too expensive to manufacture, and the accuracy of firing bullets with leading belts, crumpled when fired, left much to be desired.
The second design solution in the field of sub-caliber bullets is the developments of the American company AAI, headed by its head Irwin Barr, which in 1952 developed a 12-gauge rifle cartridge equipped with 32 arrow-shaped striking elements placed in a container-type push pallet. Tests have shown that arrow-shaped bullets have a large damaging effect, but they have low firing accuracy due to the impossibility of ensuring the specified direction of the bullets flight after their group departure from the barrel.
Initiative work continued under the US Army SALVO research program. AAI has developed a single-bullet cartridge XM110 caliber 5, 6x53 mm with a large elongation sleeve, equipped with a steel arrow-shaped sub-caliber bullet with a diameter of 1, 8 mm and caliber tail. As a leading device, a pulling pan made of magnesium alloy was used, which was cut into parts by a muzzle attachment after the bullet exited the barrel. Shooting was carried out from small arms with a smooth barrel, the stabilization of the bullet in flight was provided by the tail unit. Aerodynamic bevels on the empennage planes set a small angular velocity of rotation of the bullet in order to average the effect on the straightness of flight of manufacturing defects in its manufacture.
During the experiments, an improved version of cartridge 5, 77x57V XM645 was developed, which used a composite four-segment pulling pan made of fiberglass with a Teflon coating, held on the bullet in the barrel due to frictional forces and disintegrated into segments under the influence of air pressure after the bullet was ejected from the barrel. The length of the cartridge was 63 mm, the length of the arrow-shaped bullet was 57 mm, the weight of the bullet was 0.74 grams, the pallet was 0.6 grams, the muzzle velocity of the bullet was 1400 m / s
However, in an effort to provide the greatest elongation of the bullet, AAI had to go for lengthening the cartridge case, which negatively affected the reliability of the reloading mechanism due to high friction in the chamber, and also led to an increase in the size and weight of the receiver of small arms.
Therefore, in the next program of the US Army called SPIW, cartridge 5, 6x44 XM144, developed by the Frankfort Arsenal in the form factor of a low-impulse cartridge 5, 56x45 mm, became the leader. An improved version of the XM216 SFR cartridge had a standard sleeve, the length of the cartridge was 49.7 mm, the length of the arrow-shaped bullet was 45 mm, the weight of the bullet was 0.65 grams, the weight of the pallet was 0.15 grams, the muzzle velocity of the bullet was 1400 m / s
Experimental firing conducted within the framework of the SALVO and SPIW programs using sub-caliber arrow-shaped ultra-low-mass bullets revealed the fatal drawbacks of such bullets - increased lateral drift under the influence of wind and a significant deviation from the specified trajectory when firing in the rain.
In the Soviet Union, the first cartridge 7, 62 / 3x54 mm with a sub-caliber arrow-shaped bullet was developed under the leadership of Dmitry Shiryaev in the early 1960s at NII-61 (future TsNIITOCHMASH). The arrow-shaped bullet differed from its American counterparts in its greater mass, lower elongation (3x51 mm), the absence of narrowing in the tail area and, most importantly, the method of connecting the pallet and the bullet with the help of a comb applied to the arrow shaft. This solution made it possible to provide the necessary adhesion with a greater tractive effort from the side of the pallet to propel a bullet with a multiple of the mass than its American counterparts.
The two-piece pallet was made of aluminum alloy, therefore, when flying apart after leaving the barrel, it posed a certain danger to neighboring shooters. In addition, aluminum intensively adhered to the surface of the barrel bore, which required dry cleaning of the barrel every 100-200 shots. But the most negative property of arrow-shaped bullets turned out to be their low lethal effect on manpower - high-speed bullets perfectly pierced armor and, like needles, passed through soft tissues, without causing a shock water hammer and without forming a wound channel of large diameter.
In connection with these circumstances, in 1965, under the leadership of Vladislav Dvoryaninov, the development of a new cartridge of 10/4, 5x54 mm caliber with an arrow-shaped bullet of a modified design with a weight increased to 4.5 grams was started. During the development, a polymer material was used to make a pallet that does not pollute the barrel bore during a shot, a tail narrowing of the shaft (as in American counterparts) was used to increase the ballistic coefficient, and a cross-cut of the shaft was formed in the area of the comb and flat on the bullet point with the aim accordingly, the constructive weakening of the bullet for breaking into two parts and overturning the bullet in the process of penetrating soft tissues
These technical solutions made it possible to increase the lethal effect of arrow-shaped bullets, but at the same time reduced the degree of penetration of personal armored protection for infantrymen, since a bullet passing through a solid barrier also experiences bending stresses (increasing with an increase in the angle of meeting of a bullet with an obstacle), which lead to the destruction of the bullet shaft, twice weakened (with a comb and a cut) in the most critical section, directly adjacent to the point. The gain in lethal action and the loss in the penetrating action did not allow the adoption of sub-caliber arrow-shaped bullets designed by Dvoryaninov et al.
The study of the process of flow around various bodies in a wind tunnel with supersonic air flow revealed that arrow-shaped bullets of any design have a non-optimal aerodynamic shape - they generate five shock wave fronts at once:
- head front;
- the front at the point of transition of the point to the shaft;
- front on the leading edges of the tail;
- front on the trailing edges of the tail;
- the front at the point of the tail constriction of the shaft.
For comparison, an ogival-shaped caliber bullet at supersonic speed generates only three shock wave fronts:
- head front;
- front at the point of transition of the tip into the cylindrical part;
- tail front.
The most optimal from the point of view of the aerodynamics of supersonic flight is the conical shape of the bullet without fracture of the generating surface and without the tail, which generates only two fronts of the shock wave: head and tail. In this case, the opening angle of the head front of the conical bullet is several times less than the opening angle of the head front of the swept bullet due to the smaller opening angle of the tip of the first compared to the opening angle of the second cone. In addition, the arrow-shaped bullet, fired from a smooth barrel and untwisted in flight (in order to compensate for manufacturing defects) due to the bevels of the tail, is also distinguished by increased braking due to the selection of part of the kinetic energy for the bullet spinning.
In connection with the indicated shortcomings of arrow-shaped bullets, an innovative cartridge under the title "Spear" / SPEAR is offered, equipped with a sub-caliber conical bullet with a pushing pan that does not require a comb on the body of the bullet. The cartridge is made in a telescopic form factor in order to minimize the packaging volume, which is determined only by the length and largest diameter of its sleeve. The cartridge is intended as an ammunition for small arms equipped with a barrel with an oval-screw boring, bored like Lancaster for the purpose of twisting the bullet in the process of passing the barrel bore. The bullet in flight maintains stability both due to the gyroscopic moment and due to the forward displacement of the center of gravity relative to the center of aerodynamic pressure by the formation of an internal cavity in the tail of the bullet.
A conical bullet fired from a Lancaster barrel has an improved ballistic coefficient compared to both ogive and arrow-shaped bullets for the following reasons:
- the smallest number of shock wave fronts generated during supersonic flight;
- no loss of kinetic energy for bullet spinning due to the incoming air flow.
A conical bullet with an inner cavity in the tail section also has an increased penetrating ability - in the process of passing through a solid barrier, the tail section is crumpled inward and the diameter of the cone base decreases to the diameter of the bullet in the section of the beginning of the cavity. The transverse load of the bullet is almost doubled. In this case, the sharpness of the preserved conical surface of the bullet remains greater than that of an ogive or arrow-shaped bullet of equal length. The absence of a comb and transverse cuts on the surface of the conical bullet additionally increases its penetration in comparison with the arrow-shaped bullet designed by Dvoryaninov et al.
At the same time, a conical bullet with an internal cavity in the tail section has a high lethal effect, since:
- it is on the verge of stability due to the gentle pitch of the screw thread of the Lancaster bore;
- after breaking through an armored barrier, its stability decreases due to crushing of the tail section and displacement of the center of pressure beyond the center of gravity.
Losses of kinetic energy for breaking through an armor barrier for a conical bullet with an internal cavity are at the level of arrow-shaped and ogival bullets: in the former, energy is spent on crushing the body in the region of the cavity, in the second, on cutting the tail unit, in the third, on crushing and tearing the shell and shirt from core.
The body of the conical bullet functionally corresponds to the core of the sheathed bullet, there is no lead jacket, instead of a shell made of heavy and expensive brass, a pallet made of light and cheap plastic is used. On the other hand, a conical bullet most rationally uses the strength characteristics of its structural material in comparison with an arrow-shaped bullet, artificially weakened in the place of the comb and the cross-cut. Therefore, the mass of a conical bullet can be significantly minimized in comparison with an ogival and arrow-shaped bullet with equal penetration. This makes it possible to make an economically justified choice of the constructional material of the conical bullet in favor of the tungsten metal alloy, which has the highest density.
Due to the limited internal volume of the telescopic cartridge, it is proposed to use a propellant charge in the form of a pressed powder checker with the addition of crystalline HMX granules (the size of which is less than the critical diameter of detonation of an explosive) in order to ensure the design rate of combustion of the charge for the selected barrel length of small arms. In order to reduce the total weight of the cartridge as a structural material of its sleeve, it is proposed to use a composite alloy of aluminum and dispersed fiber of aluminum oxide, protected by a galvanized brass coating and an antifriction polymer coating with graphite filling, described in the article "Promising cartridges for rifled weapons" ("Military Review "Dated December 9, 2017).
The following table provides a comparative assessment of different types of cartridges and small arms bullets:
As can be seen from the table, the "Spear" / SPEAR cartridge is the leader in terms of minimum packing volume, length and weight, as well as in lateral load of a bullet. The total recoil momentum of its bullet, pan and powder gases is about 1/3 higher than the total recoil momentum of the bullet and powder gases of the cartridge 5, 45x39 mm, while the muzzle energy of the former is exceeded by 1/7 compared to the second.
In addition, when firing a bullet in a polymer pallet from a barrel with an oval-screw drilling, there is practically no thermoplastic wear of the barrel bore due to the absence of grooves. In this regard, an increase of more than 1.5 times the initial speed of a bullet will not affect the resource of small arms. Moreover, a wearless shot creates a reserve for increasing the rate of fire in fixed bursts to the level of 2000-3000 rounds per minute, which was recommended by the GRAU commission of the Ministry of Defense of the Russian Federation following the results of the Abakan competition in order to increase the accuracy of automatic firing from uncomfortable positions.
In addition to small arms ammunition, the "Spear" / SPEAR cartridge can be used as ammunition for hunting weapons with Lancaster barrels of the IZH-27 type using standard plastic sleeves filled with chiseled conical bullets made of steel or brass in a segmented pallet made of molded thermoplastic. While maintaining the recoil of the weapon at the firing level of a conventional 12-gauge shot, a sub-caliber bullet weighing 9 grams will accelerate in a 70 cm barrel to a speed of 900 m / s, which corresponds to the characteristics of the Mosin three-line rifle.
Geometric characteristics of various types of conical bullets (length, cone opening angle, degree of roundness / biconicity of the head end, presence on the tip of a contact area for crushing an armored barrier or an expansive cavity for lethality of shooting at a large animal, depth and thickness of the walls of the tail cavity), taking into account the specified flight speeds and the targets to be hit can be determined on the basis of simulating the passage of bullets in air, gel or solid media using the domestic software product FlowVision.
