from: Polskie konstrukcje broni strzeleckiej /
20 mm ammunition of Polish production
Simultaneously with the undertaking of work on the Polish 20 mm heaviest rifle the machine was started to create its own ammunition of this caliber. Initial work was undertaken by the Ammunition Factory in Skarżysko, in 1936, on its own expense. The research material she initially had was composed only of from a catalog with a very sketchy description and two original cartridges of the company
"Solothurn." Only later, after the drawing by the factory Ammunition of main types of ammunition, Department of Small Arms ITU he sent catalogs and more ammunition patterns of this caliber of other companies.
Comparative tests of the “Solothurn” ammunition carried out at that time,“Oerlikon” and “Madsen” showed that it is almost equivalent.Therefore, it was decided to remain on the “Solothurn” ammunition asstarting material.The work program consisted of:
- development of the cartridge case and chamber,
- development of a training projectile AA,
- developing a training-tracer projectile AA,
- developing an explosive-tracer AA projectile. with a high-sensitivity igniter,
- developing a training anti-tank projectile,
- elaboration of an explosive-tracer anti-tank projectile with an igniterbottom.
According to the program, the Factory of Ammunition in Skarżysko joined to develop the husk, while designing a cartridge chamber with it future weapon. The designed scale had a capacity of 3 cm3 greater than the scale the “Solothurn” company, which allowed to assume that it would give faster speed initial projectile. At several conferences held in 1937. with the representatives of the Rifle Factory in Warsaw finally established drawings of the cartridge chamber, according to which chambers were made in 20 mm nkm model A. In order to quickly deliver scales to the Rifle Factory, the first of them made by turning with steel rods. Plans were also developed production of turned brass scales.
Due to advanced works on Polish NKM, it was created the need for a special gunpowder for 20mm ammunition. Deelaborations therefore, the cartridges of the companies “Solothurn” and “Oerlikon”, and powder from them, which samples were sent to PWP “Pionki” with a request for development and execution Polish gunpowder with similar properties.
When designing missiles, work was first undertaken above the projectile. - explosive-light with a very sensitive igniter and exercise. It was assumed that the first one should be very good visible in the day streak and igniter working when hit the canvas airline. In addition, it was assumed that the construction of the fuse should be such that
in the case of failure to hit the target, the projectile did not fall entirely into the nausea, but yielded self-destruction. As a self-destructor, a smothering smudge was used here, which caused ignition of the fire switch from which it caught fire pentryt - explosive located in the projectile. The combustion took place so violently that it caused a large and sudden increase in the pressure it blew up fuse with shell threads. At the same time, the acceleration obtained was yes big, that the trigger of the detonator, placed loosely, hit the incandescent, causing the projectile to explode.
In the second place, a training projectil AA was started, which in terms of ballistics should have features of an acute projectile. Ammunition of this type was also needed by the Rifle Factory to try to act NKM. At the same time, the Ammunition Factory in Skarżysko was preparing for assemble and merge cartridges by adapting appropriate instruments for this purpose and machines. They were made on them in the second half of 1937 to merge the first lots of training AA bullets. with steel scales filled to the massa normal substitute material instead of gunpowder. This ammunition has been sent to The Rifle Factory was used to try out the mechanisms of weapons.
On November 1, 1937, the Factory in Skarżysko received a barrel from the Rifle Factory pressure, and with PWP “Pionki” a sample of gunpowder marked with the symbol BN.II.
Therefore, information shooting with training cartridges was carried out, comparing Polish dust with the Solothurn company’s dust the cartridges received a 40 g powder charge. Some of them also received additionally, black powder ballast.
The research showed a significant superiority of the powder of Polish production, because the projectile velocity was obtained 903,9 m / s at a pressure of 3,380 kg / cm2, while powder “Solothurn” will allow) to obtain 886 m / s at a pressure of 3460 kg / cm2.
It also turned out that it is necessary to use black powder ballast. The shooting, however, did not end in full success, she left in fact, the stabilization of the cartridges, which gave the shields on the backslash, was evident. After investigating the causes of this phenomenon, it turned out that the pressure barrel from which shooting was carried out, it had a badly made thread. Instead of being planned in stroke drawings equal to 720 mm, it had a progressive stroke of 2500-1800 mm. Conducted on 27.10.1937 new tests after receiving a good barrel showed very good stabilization of bullets. Positive results were started in Skarżysko to produce more exercise cartridges with case steel and a larger batch of gunpowder B.N.II was ordered in “Pionki”. At the same time, preparations were made to begin production of brass case.
On November 21, 1937, they were shot at a pressure increased to 4500 kg / cm2, first brass case. Shooting took place with the gap spacing extended by 10.3 mm. The scales were able to withstand 3 such shots without necessity undergo reconstruction. Attempts have also not revealed any defects in the form cracks, streaks or gas outflow on the incinerator, therefore a larger number of them were started. The made shells were merged in cartridges AA excercise. Practice and number of 2000 items were sent to the SmallArms Gun Department in Zielonka.
At the same time, a highly sensitive fuse was being developed in Skarżysko for AA bullets. The bullets consisted of: a shell, a fuse, a sleeve with bottom cap, in which light mass has been pressed, fire connector with pressed black powder and explosive material (pentryt).
The design drawings were modeled on bullets Solothurn, where the detonator was constructed completely different. The fuse protection was centrifugal. The spire rested on two weights having an external conical and embedded surface in the appropriate fuse socket. Weights were pressed spiral spring. After the shot, due to the centrifugal force, these weights they moved outside, rising at the same time by moving around the surface of the conical hull. At maximum extension of the weight they released the firing pin. The igniter then became unprotected and armed. High the sensitivity of the detonator was sought to be achieved using a light needle made of duralumin and by resigning to place the spring between the primer igniter and spire. The sensitivity of the fuse had to be large because of the requirements these types of fuses forced them to act between two