In the first months of the war in the hands of Soviet specialists were a captured sample of a 47-mm sub-caliber projectile of the then non-existent Polish army and a German memo on the use of cartridges with a 37-mm special armor-piercing projectile of the “40” model. It was not possible to get a real sample of the German sub-caliber projectile, so the engineers had to use the translated manual. In it, in particular, German specialists wrote:
These ammunition are used to combat highly armored targets at a distance of 0 to 300 meters. At distances exceeding 300 meters, the use of these ammunition is useless; therefore, when shooting at distances exceeding 300 meters, normal armor-piercing shells should be used.
A crew of Soviet artillerymen fires a 45-mm anti-tank gun of the 1937 model (53-K) at a German tank on the street of the village. The crew number gives the loader a 45-mm sub-caliber projectile. Source: waralbum.ru
This thesis very clearly demonstrates the real advantage of sub-caliber projectiles, which are considered by some experts to be almost an absolute weapon against Soviet armored vehicles. Based on the data of the German training manual and the only captured 37-mm Polish shell, the Main Artillery Directorate of the Red Army proposed to develop its own analogues. At the end of August 1941, with this non-trivial task, they turned to NII-24 or, as it is better known, the Armored Institute.
For obvious reasons, the engineers were unable to restore the drawing of the 37-mm German APCR shell, but they could cope with the 47-mm Polish one. It turned out that the trophy sample of the sub-caliber projectile was an exact copy of a 47-mm similar projectile of the French company “Komissan”. As a result, it was decided to develop domestic versions of armor-piercing sub-caliber for 45-mm and 76-mm in full accordance with French patterns.
At NII-24, the topic of the development of domestic subcaliber projectiles received the number 5044 and the name “45-mm and 76-mm armor-piercing subcaliber projectiles similar to the shells of the French company” Komissan “. It should be noted that the engineers managed to create and test prototypes by September 1941. I would like to emphasize that the ammunition was developed and manufactured in an experimental batch in just a few weeks!
The 45 mm projectile received the internal code 2-1742. The ammunition weighed 850 grams, of which 270 grams fell on the carbide core. For the 76-mm sub-caliber projectile, the index 2-1741 was dispatched, and it, of course, differed in a greater mass of 3.65 kg, of which a little more than one and a half kilograms fell on the core.
45-mm APCR projectile. Drawing 2-1742. Source: Report NII-48
The prototypes were made according to the drawings of the NII-24 in a pilot plant attached to the institute. A total of 40 subcaliber rounds, 20 of each caliber, were produced. As a core for 45-mm and 76-mm projectiles, a single tool alloy steel KHVG was used, which is an alloy of tungsten (1.49%), chromium (1%), sulfur (0.023%), phosphorus (0.011%), silicon (0.24%), manganese (0.24%) and carbon (0.97%). Everything else, naturally, was occupied by iron. The main alloying elements were chromium and tungsten. The sabot pan was made of st35 steel, and it was identical to the core material, with the exception of expensive chrome and tungsten.
76.2-mm APCR experienced projectile. Drawing 2-1741. Source: Report NII-48
Briefly about the heat treatment of the core material of armor-piercing shells. In many ways, it was this process that determined the mechanical properties of steel. In accordance with the technology, the core blank was first hardened. Heat treatment technologies for the 45-mm and 76-mm differed slightly. Initially, the products were heated to 600 degrees, then they were heated to 830 degrees for 50 minutes (the core of the 76-mm projectile was heated for 1 hour) and, finally, they were kept at a maximum temperature for 10-15 minutes. There were significant differences in the cooling procedure. The smallest billet was cooled in kerosene, and the larger one – in water at a temperature of 45 degrees.
After hardening the core, tempering followed. The items were again heated to 220-230 degrees, held for an hour and a half, and slowly cooled in air.
Testing 45 mm caliber
Fire tests of subcaliber shells samples took place on September 6-7, 1941 at the Sofrinsky test site and turned out to be discouraging. The assignment to the testers was as follows:
According to the test program, it was necessary to determine the armor penetration of projectiles up to 300 meters and at the same time select normal charges by pressure with the determination of the initial speed and speed drop at a distance of 300 meters.
As a target were chosen armor plates with a thickness of 50, 60 and 70 mm, installed at an angle of 30 degrees. They hit them with experimental shells from a distance of 100-200 meters from a 45-mm cannon of the 1932 model, a 76-mm regimental cannon of the 1927 model and a 76-mm divisional gun of the 1902/30 model. The last two guns, frankly, are not the most anti-tank and not the freshest. The testers even counted the number of shots that the guns fired before testing the sub-caliber shells: for the 45-mm gun – 1717 shots, for the most worn-out 76-mm sample of 1927 – 3632 and for the 76-mm sample 1902/30 – 1531.
45-mm anti-tank gun model 1932, used for testing prototype shells. Source: ru.wikipedia.org
The conclusions on the fire tests were disappointing. 45-mm APCR shells from a distance of 100-200 meters could not penetrate the 50-mm armor plate in four cases out of eleven. The testers recorded only one conditioned penetrating defeat and as many as six blinds. At the same time, the initial speed of the ammunition approached 950 m / s. The testers noted that firing 45-mm projectiles was accompanied by large dispersion, the cause of which was the unstable flight of the ammunition due to cutting off the belt or turning the core. A conventional armor-piercing or, as it was called, a 45-mm projectile of the “standard drawing” could not hit similar armor.
Subcaliber 76-mm shells were used to hit the armor plates from two cannons. The short-barreled regimental gun, as expected, could not disperse the armor-piercing projectile to speeds above 535 m / s, which negatively affected the efficiency. Nevertheless, the 50-mm homogeneous armor was pierced by the experienced projectile, in contrast to the standard ammunition of a similar caliber. For a 50-mm cemented armor plate, out of three hits, only one was counted as conditional. Against a 60-mm cemented slab, the new sub-caliber projectile was powerless.
The divisional gun of the 1902/30 model, due to the long barrel, provided the anti-tank projectile with a much higher muzzle velocity – 950 m / s. On the 50-mm cemented armor, the projectile was not even tested, obviously, there was an understanding of its excess power. They fired ten times at 60-mm cemented, of which nine were not counted, and only one shell pierced the target through and through. Against thicker 70-mm armor, 2 substandard defeats were recorded. In all test episodes, the shelling was carried out from 100-200 meters.
76-mm regimental gun model 1927, used in tests. Not the best example for fighting tanks. Source: ru.wikipedia.org
Now let’s move on to the conclusions of the main developer of the NII-24 shells. The engineers decided that shells of this design did not show advantages over standard armor-piercing ammunition. Moreover, according to NII-24: “Further work in general on sub-caliber projectiles in the case of the manufacture of a core (active projectile) from instrumental or structural steel with a specific gravity of about 7.84 should be stopped.” This is how the defense industry of the USSR almost lost the most progressive anti-tank type of projectile! NII-24 engineers claimed in a report that they came to this conclusion, not only testing their own shells, but also examining captured samples. The German core contained up to 75% tungsten, had a specific gravity of 16.5 and a Rockwell hardness of about 70 units, but it could not impress domestic gunsmiths either. True, in a top secret report, the engineers did not reveal what exactly the German ammunition did not please them.
It’s not all bad
The specter of hope for the further development of domestic sub-caliber projectiles gives the last point in the conclusion of the NII-24:
Work on the final clarification of the feasibility of using subcaliber armor-piercing projectiles should be carried out in the case when the issue of producing a sufficient amount of hard alloys for the needs of the shell industry is positively resolved and the problem of the possibility of machining hard alloy cores for such shells in mass production is solved.
For March 1942, when the report was signed, a murderous wish, to put it bluntly. It was with difficulty that it was possible to organize production at the evacuated enterprises, and then the requirement to master the mass processing of tungsten alloys.
76-mm divisional gun model 1902/30. Source: ru.wikipedia.org
The Artillery Committee of the Main Artillery Directorate read the report with interest, and one of the military engineers wrote by hand on the title page:
The report does not indicate the resistance coefficients of the slabs used for testing. The speeds at which the tests were carried out are confused, and it is not clear what thickness of armor they correspond to. These data will be updated at NII-24. The conclusion of the NII-24 is correct in terms of evaluating the results and in terms of using a core with a specific gravity of 7-8 in this design and incorrect in terms of refusing to search for new, more advanced designs of sub-caliber projectiles, which make it possible to replace the “heavy” core with its design. Take note of the report.
Perhaps it was this military expert, whose signature cannot be made out, who saved the domestic armor-piercing sub-caliber shells.