"Stalker" is a Russian Language movie by Andrei Tarkovsky. The movie is loosely based on Roadside Picnic, a 1972 novel by Russian science fiction authors Boris and Arkady Strugatsky, who also wrote the screenplay. Despite being filmed entirely in Estonia (a USSR Republic at the time) the film was released internationally under the English Title "Stalker". The film takes place in "The Zone", an area with no specific time or location. The film is very peaceful, and instead uses firearms as symbols rather than for action scenes. This film was a partial inspiration for the 2007 Videogame S.T.A.L.K.E.R.: Shadow of Chernobyl, and many of its elements were incorporated into the game.
One of the scenes features Writer (Anatoly Solonitsyn) taking out a WW2-era Hungarian Femaru 37M before opening a closed door. He is asked to leave it, as "Zone" is not a good place to go around waving weapons. Moments later we see Stalker (Alexander Kaidanovsky) pushing the pistol further into the water, out of the sight.
In the dream sequence we can see a Thompson Submachine Gun submerged in water. It is difficult to discern the exact model, but it is most likely a M1928A1 Thompson. The Soviet Union received a number of M1928A1s during WWII as part of lend-lease program. They were included as standard equipment in M3 light tanks, but never used because .45 ACP ammunition was not standard in Russia at the time. It is possible that the film makers could have obtained on of these military surplus weapons. Another Thompson is seen being fired by one of the guards at the Zone checkpoint.
When three movie protagonists illegally enter the Zone through a checkpoint, the guards start shooting at them. A Thompson (see above) and another unidentified rifle/machine gun on a bipod are used by guards. Unfortunately there is no other take and this weapon probably cannot be identified.