How a SVT-40 Rifle Works

Wikipedia: In the early 1930s, the Soviet Union requested the development of a semi-automatic rifle to replace the Mosin-Nagant, taking inspiration from the Mexican Mondragón rifle. The design was left up to two individuals, Sergei Simonov and Fedor Tokarev.[7] Simonov, who had experience in developing the Fedorov Avtomat, created a prototype for the AVS-36 in 1931, which was used during the Winter War but due to design flaws it was removed from service by 1941.

SVT-38:
In 1938, Tokarev's rifle was accepted for production, under the designation SVT-38 with hopes that it would become the new standard issue rifle of the Red Army. Ambitious production plans anticipated two million rifles per year by 1942. Production began at Tula Arsenal in July 1939 (production at Izhmash began in late 1939).

The SVT-38 is a gas-operated rifle with a short-stroke, spring-loaded piston above the barrel and a tilting bolt,[1] a system that would later be used in the FN FAL.[9] The SVT-38 was equipped with a bayonet and a 10-round detachable magazine. The receiver was open-top, which enabled reloading of the magazine using five-round Mosin–Nagant stripper clips.[9] The sniper variant had an additional locking notch for a see-through scope mount and was equipped with a 3.5×21 PU telescopic sight.

The SVT-38 saw its combat debut in the 1939–1940 Winter War with Finland. The rifle had many design flaws, as its gas port was prone to fouling, the magazine would sometimes fall out during use, and it was inaccurate, only being effective up to 600m.[9] Production of the SVT-38 was terminated in April 1940 after some 150,000 examples had been manufactured.

SVT-40:
With the removal of the SVT-38 from service, an improved design, the SVT-40, entered production. It was a more refined, lighter design incorporating a modified, folding, magazine release. The hand guard was now of one-piece construction and the cleaning rod was housed under the barrel. Other changes were made to simplify manufacturing. Production of the improved version began in July 1940 at Tula and later at factories in Izhevsk and Podolsk. Production of the Mosin–Nagant M1891/30 bolt-action rifle continued and it remained the standard-issue rifle to Red Army troops, with the SVT-40 more often issued to non-commissioned officers[citation needed] and elite units like the naval infantry. Since these factories already had experience manufacturing the SVT-38, output increased quickly and an estimated 70,000 SVT-40s were produced in 1940.

By the time of Operation Barbarossa, the German invasion of the USSR in June 1941, the SVT-40 was already in widespread use by the Red Army. In a Soviet infantry division's table of organization and equipment, one-third of rifles were supposed to be SVTs, though in practice they seldom achieved this ratio. The first months of the war were disastrous for the Soviet Union; they lost hundreds of thousands of SVT-40s. To make up for this, the production of the Mosin–Nagant rifles was reintroduced. In contrast, the SVT was more difficult to manufacture, and troops with only rudimentary training had difficulty maintaining it. Submachine guns like the PPSh-41 had proven their value as simple, cheap, and effective weapons to supplement infantry firepower. This led to a gradual decline in SVT production. In 1941, over one million SVTs were produced but in 1942 Izhevsk arsenal was ordered to cease SVT production and switch back to the Mosin–Nagant 91/30. Only 264,000 SVTs were manufactured in 1942 and production continued to diminish until the order to cease production was finally given in January 1945. Total production of the SVT-38/40 was around 1,600,000 rifles, of which 51,710 were the SVT-40 sniper variant.
A 1941 Tula SVT-40 in original sniper configuration.

AVT-40 automatic rifle
To supplement the Red Army's shortage of machine guns, an SVT version capable of full-automatic fire (designated the AVT-40) was ordered into production on 20 May 1942; the first batches reached the troops in July.[11] It was externally similar to the SVT, but its modified safety also acted as a fire selector allowing for both semi-automatic and fully automatic fire modes. When fired automatically the rifle had a rate of fire of approximately 750 RPM, faster than even the DP machine gun which fired the same cartridge at 550 RPM. o better resist the stress of automatic fire, the AVT featured a slightly stouter stock made of hardwood usually distinguished with a large “A” engraved in it; surplus AVT stocks were later used on refurbished SVTs. In service, the AVT proved a disappointment: the automatic fire was largely uncontrollable, and the rifles often suffered breakages under the increased strain.