The PPS-43, designed by Alexei Sudayev based on a previous submachine gun design by I.K. Bezruchko-Vysotsky, was the Soviet replacement for the PPSh-41. The Shpagin submachine gun was a very effective combat weapon, but was time-consuming to produce and required specialized manufacturing tools. The Soviet military wanted a weapon that was cheaper and faster to make, and which could be produced at small shops not experienced in firearms production. The Sudayev design fit these criteria extremely well, being made almost entirely of simple bent mates components.
Production of the first prototype Sudayev submachine guns begin in 1942 in the besieged city of Leningrad, where guns were quite literally taken from the factory door to the front lines and put into service. A few minor flaws were discovered and corrected, and by the time the siege was broken the gun was suitable for mass production. It was designated the PPS-43, and while it was theoretically a replacement for the PPSh-41, it never did actually replace the former weapon. It was decided to continue PPSh-41 production in the factories already tooled up for it, while making use of the PPS-43’s simplicity to put it into production as a range of new factories that did not have the technical capacity to make more complex weapons.
Mechanically, the PPS-43 was a simple blowback gun, using basically the same conceptual operating system as the PPSH-41. However, Sudayev resolved the most significant practical problem with the PPSH-41 by abandoning its unreliable drums and developing his own new double stack, double feed 35-round box magazine. The PPS-43 magazine is simpler to load, more reliable in used, and much smoother to insert and remove from the weapon that then PPSh magazines. The improvement was substantial enough to justify the use of different and incompatible magazines in the two guns. In conjunction with the discarding of the drum magazine, Sudayev also designed his gun to have a lower rate of fire than the PPSh, to better manage ammunition supply. However, the roughly 600 rpm rate of the PPS-43 is actually relatively difficult to control in that light weapon, where the PPSh-41 was substantially smoother shooting despite (or perhaps because of) firing faster.