The film begins with a sequence (supplemented by subsequent flashbacks) in which Mikhail Kalashnikov, a young farmer’s son from Altai, is seen secretly working on a functional toy rifle. The film switches to the year 1941, in the midst of World War II, where the now adult senior sergeant Kalashnikov serves as a tank commander in the Red Army. During the Battle of Bryansk, Kalashnikov is seriously wounded while taking out a German anti-tank gun, and he is taken off the frontlines.
While being transported to the rear, he and a companion encounter a group of German soldiers, and he witnesses his comrade’s new submachine gun failing at a critical moment due to design faults in the magazine. This inspires him to use his self-acquired talent at inventing to design a new automatic weapon for the Soviet army.
On his way home, Kalashnikov visits Matai Station in Kazakhstan, where he previously worked as an engineer but was dismissed for using the depot’s workshop to build his private weapon designs. He appeals to his former superior, Krotov, to let him assemble his latest invention, but Krotov refuses. When Kalashnikov proposes his design to a passing high-ranking officer named Basarov, he gets authorization to proceed, and with the help of the workers he successfully assembles his new submachine gun.
While trying to bring it to Basarov, he is mistakenly arrested, but an ordnance officer takes notice of the gun’s innovative design and has it sent off for evaluation. As a result, Kalashnikov is released and encouraged to present his gun to General Pavel Kurbatkin, the district commander of Central Asia, who approves him for a national arms design competition.