45 mm semi-automatic universal cannon 21-K

45 mm semi-automatic universal cannon 21-K
Semi-automatic cannon of 45 mm caliber, which was in service of the USSR Navy in the 1930s-1950s. The 21-K artillery system, according to the design documentation, is an adaptation of the 1932 model 45-mm anti-tank gun (19-K) to a naval machine gun. The body of the 21-K gun was borrowed from the 19-K cannon and consisted of a stapled barrel and casing. Since before 1935 semi-automatic bolt had not been mastered at Factory No.8, all guns manufactured by the factory until 1935 did not have a semi-automatic bolt. The bolt closed when the next cartridge was inserted, and opened manually. The 21-K systems, made after 1935, featured a semi-automatic inertia-type bolt that opened automatically after firing.
The barrel of the 21-K consisted of a tube and a casing, put on the tube when hot and made in one piece with the breechblock of the gun. Guns of later production had a monoblock barrel. The barrel of the gun was a bollard. The gun had no shield.