The Mosin–Nagant was adapted as a sniper rifle in 1932 and was issued to Soviet snipers. It served quite prominently in the brutal urban battles on the Eastern Front, such as the Battle of Stalingrad, which made heroes of snipers like Vasily Grigoryevich Zaitsev and Ivan Sidorenko. The sniper rifles were very much respected for being very rugged, reliable, accurate, and easy to maintain. Finland also employed the Mosin–Nagant as a sniper rifle, with similar success. For example, Simo Häyhä is credited with killing 505 Soviet soldiers using his M28 Mosin–Nagant.[6]
In 1936, the 91/30 was again modified, this time to speed production. The receiver was changed from its octagonal shape (colloquially referred to as a "hex receiver" for reasons that are not clear) to an easier to make round receiver. When war with Germany broke out, the need to produce Mosin Nagants in vast quantities led to a falling-off in finish of the rifles. The wartime Mosins are easily identified by the presence of tool marks and rough finishing that never would have passed the inspectors in peacetime. However, the functionality of the Mosins was unimpaired.
By the end of the war, approximately 17.4 million M91/30 rifles had been produced.
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Model 1891/30 (винтовка образца 1891/30-го года, винтовка Мосина) – The most prolific version of the Mosin–Nagant. It was produced for standard issue to all Soviet infantry from 1930 to 1945. Most Dragoon rifles were also converted to the M1891/30 standard. It was commonly used as a sniper rifle in World War II. Early sniper versions had a 4x PE or PEM scope, a Soviet-made copy of a Zeiss design, while later rifles used smaller, simpler, and easier-to-produce 3.5x PU scopes. Because the scope was mounted above the chamber, the bolt handle was replaced with a longer, bent version on sniper rifles so the shooter could work the bolt without the scope interfering with it. Its design was based on the Dragoon rifle with the following modifications:
Flat rear sights and restamping of sights in metres, instead of arshinii.
A cylindrical receiver, replacing the octagonal (commonly called "hex") one. Early production rifles (from 1930 to 1936) and converted Dragoon rifles retain the "hex" receiver.
A hooded post front sight, replacing the blade on previous weapons.
I really don't think the russians were using finn rifles then