Fede, this is a very interesting document!
Not that I can say anything about the ammunition but 1931 fits well into the time period when the USSR was trialing and developing the own 12.7x108 cartridge and Russian sources mention that even a copy of the .50 M2 chambered in 12.7x108 was tested (made in Russia to what I understood).
Alex, thanks, interesting thought. I’m really curious about the purpose of this ammunition, even if this sale was never approved.
IN the Late Twenties and early 1930s, Stalin’s Soviet Union was combing the world for all sorts of Equipment (Military and Non-military)…example, they ordered and had delivered, massive Beyer Garret articulated locomotives from UK, Heavy Electric Locomotives from Ansaldo (Italy) ,heavy steam Locos from Alco and Baldwin, on Union Pacific Designs; the list goes on and on. The USSR also had several German (Weimar) Tank development factories in the Ukraine, and the Wehrmacht regularly conducted flat land exercises there with armour.
After WW I, the Soviets first worked with the German MG18 (TuF MG) and its ammo, the 13x92SR; they also had examples of Browning’s first ( 1921) MGs, both WC and AC. .50 cal ammo was probably supplied initially by FN, which incidentally was also making 13mm T18 ammo for China in the 20s. They would have followed the Vickers developments (12,7x81 SR,) as well as the Breda counterpart.
An order for only 5,000 rounds was probably for a “comparison shoot” ( using a Known standard to derived new data from experimental ammo, as in a 12,7x108 cartridge.).
All these “studies” led to the designs used successfully in WWII ( T26 and T34 Tanks, FD series Locomotives (2-10-0), DShK 12,7x108 etc guns and ammo.) and after…
An interesting footnote from History.
The Soviets took a very systematic approach to the business of developing automatic weapons. I recall reading that they established a college in the 1920s purely for the purpose of training gun designers. The result has been weapons which outperform any equivalents from elsewhere to this day.
Perhaps they were as interested in testing the Browning HMG as the .50 cal ammo?