Doom is a 2005 sci-fiction horror film, based on the popular Doom 3 video game developed by id Software. The movie takes place on Mars in the year 2046, and stars Karl Urban and Dwayne "The Rock" Johnson as members of the RRTS (Rapid Response Tactical Squad) tasked to investigate the happening at the Union Aerospace Corporation (UAC) Olduvai Research Facility. The movie was directed by Andrzej Bartkowiak (Exit Wounds, Romeo Must Die and Cradle 2 the Grave).
The Heckler & Koch G36 visually modified is the futuristic rifle carried by Sarge (Dwayne Johnson), Reaper (Karl Urban), Portman (Richard Brake), and Duke (Razaaq Adoti). Mac (Yao Chin) also carries what appears to be one of these rifles with some sort of grenade launcher attachment. According to the ammo counters, the beefed-up box magazines are supposed to hold 65 rounds.
Some of the marines including Mac (Yao Chin), Duke (Razaaq Adoti) and Reaper (Karl Urban) use H&K USP handguns with stainless-steel barrels as their sidearms. It is most notably seen when Mac hands one to Pinky (Dexter Fletcher) for protection.
Sarge's (Dwayne Johnson) sidearm is an IMI Desert Eagle Mark XIX. He most notably uses it to kill a mutated Dr. Carmack. His gun is quite clearly the .44 Magnum version, as evidenced by the fluted barrel in the screenshot below.
Browning M1919A4E1 (mocked up as a Handheld Minigun)
Destroyer (Deobia Oparei) uses a minigun which is actually built over a World War II Browning M1919. More specifically it appears to be the Browning M1919A4E1 judging by the bolt retracting bar visible in the behind the scenes images. The M1919A4E1 was designed for use in armored vehicles, with the bolt retracting bar allowing the machine gun to be operated more easily from inside a turret. It is built to resemble a man-portable version of the General Dynamics GAU-19/A.
The Bio Force Gun, adapted from the game's BFG 9000, also makes an appearance in the movie. Like the game, it's the most destructive weapon used. It is wielded by Sarge (Dwayne Johnson). There were two working (vibrating) props of The Bio Force Gun, built from scratch out of resin and fiberglass.
Mac carries what appears to be a modified or artificial grenade launcher type weapon attached to his rifle. This however, cannot be confirmed as the weapon is never fired in film.
