At the beginning of the war, the Mosin–Nagant 91/30 was the standard issue weapon of Soviet troops and millions of the rifles were produced and used in World War II by the largest mobilized army in history.
The Mosin–Nagant Model 1891/30 was modified and adapted as a sniper rifle from 1932 onwards with mounts and scopes from Germany at first and subsequently with domestic designs (PE, PEM) and from 1942 was issued with 3.5-power PU fixed focus scopes 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 Vasili Zaitsev and Ivan Sidorenko.
These sniper rifles were highly respected for being very rugged, reliable, accurate, and easy to maintain. In fact, some German Snipers reportedly used captured Mosin Nagants over their own Karabiner 98 rifles. Finland also employed the Mosin–Nagant as a sniper rifle, with similar success with their own designs and captured Soviet rifles. For example, Simo Häyhä is credited with killing 505 Soviet soldiers, many falling victim to his Finnish M/28-30 Mosin–Nagant rifle. Häyhä did not use a scope on his Mosin. In interviews Häyhä gave before his death, he said that the scope and mount designed by the Soviets required the shooter to expose himself too much and raise his head too high, increasing the chances of being spotted by the enemy.
In 1935–1936, the 91/30 was again modified, this time to lower production time. The octagonal receiver was changed to a round receiver. When war with Germany broke out, the need to produce Mosin–Nagants in vast quantities led to a further simplification of machining and 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, despite a lack of both aesthetic focus and uniformity, the basic functionality of the Mosins was unimpaired.
In addition, in 1938, a carbine version of the Mosin Nagant, the M38, was issued. The carbine used the same cartridge and action as other Mosins, but the barrel was shortened by eight inches to bring the weapon down to an overall length of 40 inches, with the forearm shortened in proportion.
The idea was to issue the M38 to troops such as combat engineers, signal corps, and artillerymen, who could conceivably need to defend themselves from sudden enemy advances, but whose primary duties lay behind the front lines. Significantly, the front sight of the M38 was positioned in such a way that the Model 91/30's cruciform bayonet could not be mounted to the muzzle even if a soldier obtained one.
The slaughter of the rear area troops, and increase in urban combat, led directly to the development of the Model M44 Mosin. In essence, the M44 is an M38 with a slightly modified forearm and with a permanently mounted cruciform bayonet that folds to the right when it is not needed. In terms of handiness, the M44 was an improvement on the Model 91/30, particularly for urban warfare; but few M44s saw combat on the Eastern Front.
By the end of the war, approximately 17.4 million M91/30 rifles had been produced