This is what I have just sent as my contribution to the debate:
As Bill said, most gun and ammo developments are based on previous work. Most of the automatic gun operating principles were pinned down well over a century ago, and so was ammo design: what’s happened since has mainly been a process of refinement and minor variations, with different materials anmd manufacturing techniques becoming more significant since WW2.
I have a translation of a Russian history of the 7.62mm M1943 round by Bortsov, Korablin, Lovi and Sazanov. They clearly had access to official documents when researching the history, and say the following:
“The immediate spur for the development of the new round was a meeting of the Technical Council of the People’s Commissariat for Armament (NKV) held on 15 July (1943) on the topic ‘New foreign weapons firing lower-powered rounds’. Those attending the meeting were shown trophy weapons captured form the Nazis at the front, as well as an American M1 Carbine that had been made available to the USSR for examination. The authors have been unable to find reliable information as to whether the USSR had any previous knowledge of the development of intermediate rounds in the West. The experts were particularly interested in the new German 7.92mm round with its 33mm case and the accompanying MKb42(H) carbine, which had undergone trials in the field army….Those attending the meeting…correctly judged the importance of the new German personal automatic small arms system…The meeting decided that a new reduced power round must be developed….The OKB-44 design bureau was given responsibility for developing the new round…”
I think that this report is credible because it isn’t the usual nationalistic claim, it acknowledges that the 7.62×39 was directly inspired by the German 7.92×33.
There are various other claims often made about the origin of the 7.62×39, so I’ll deal with them below:
As far as the Geco cartridge used in the Vollmer M1935 is concerned, this is dealt with in “Assault Rifle Ammunition 5.6mm to 11mm Calibre” by Peter Labbett, a specialist military ammunition historian. This was a 7.75×40 round based on the 7.92×57 case, and was therefore fatter than the 7.62×39 (11.9mm diameter rather than 11.3mm). So the Russian cartridge was not a clone of that.
Labbett goes on to describe two other Geco rounds: one from the 1930s was attributed to Winter, but this measured 7.9×33.5mm so again was different from the M1943. The final Geco round sometimes quoted as the origin of the MM1943 is the 7.62×39 Mittelpatrone, which sounds as if it might be the same – except that it is also 11.9mm in diameter and, according to Dynamit Nobel (Geco’s postwar parent company), dates from 1960.
So, there is no known German cartridge of which the 7.62×39 M1943 could have been a copy.
As far as Kalashnikov’s gun is concerned, I have not the slightest doubt that the Stg.44 was studied carefully as a part of the design process (the Russians had loads of them by then), but it was taken as a starting point for improvement rather than copied.
There’s an article on the history of assault rifles and their ammunition on my website here: quarry.nildram.co.uk/Assault.htm