You're watching a popular Science Fiction film when suddenly the argument you were about to launch over whether or not Han shot first is derailed by the realization that you saw the same weapon the night before being used by a German officer in the trenches, only then it wasn't a Frickin' Laser. The firearm equivalent of Hey, It's That Guy!, Hey, It's That Gun! is where the viewer recognizes a firearm playing a role in a world one would not expect to find it. This most frequently arises in fictional, fantastic or alien settings where prop designers are looking for something realistic, functional or available off the shelf. Is not to be confused with A.K.A.-47 where Real Life weapons are simply renamed in their proper context or Improperly Placed Firearms where they are used in an inaccurate context. This describes where a viewer is able to recognize a firearm that itself is playing a role that is accurate within the context of the work. Just like human actors, firearms may be visually modified or simply left as is. The latter is frequently the case with Cool Guns or Rare Guns, but using something that is too common/recognizable may break the viewer's Willing Suspension of Disbelief. Does not apply when an existing firearm is sufficiently modified as to be unrecognizable to anyone not using the IMFDB. Will re-apply if sufficiently modified weapons are in turn used in other works where they can be recognized from their other appearances.
- In the 1968 Planet of the Apes film the gorilla soldiers carry Lugers, which could be this or a clue that it's Earth All Along.
- The Robocop franchise has a couple good example with Robo's famous "Auto-9" handgun being played by a modified Beretta 93R and the "Cobra Assault Cannon" being played by an M82 Barrett sniper rifle.
- Said famous Auto-9 handgun reappears in the film version of City Hunter as the weapon of choice for the Big Bad.
- Serenity shows the crew finding a World War II era German Flak 30/38 20mm anti-aircraft gun and strapping it to the ship's hull to pass as reavers
- The original Star Wars films were the Trope Codifier with all weapons props being created from military surplus stocks and then visually modified to look futuristic.
- Han's DL-44 blaster is, quite obviously, a C96 "Broomhandle" Mauser pistol.
- The standard Imperial E-11 blasters were made from surplus British Sterling submachine guns.
- The DLT-19 heavy blaster rifle was a modified German MG-34 machinegun, parts of which were also used in the prequel DC-15A blaster rifle.
- The DLT-20 blaster rifle was constructed from German StG-44 assault rifles.
- In Total Recall and a number of other films set 20 Minutes into the Future the Calico Light Weapon System has become quite popular.
- In Firefly Jayne's beloved Vera was modified from a Saiga-12 combat shotgun.
- In Halo, set about five hundred or so years in the future, the UNSC apparently still uses twentieth-century South African 14.5mm anti-materiel rifles (albeit converted to semiautomatic fire and with the magazine in the bottom rather than the side of the rifle).
- In Dr. Horrible's Sing-Along Blog, the titular character's freeze ray is the same as the stun guns used by Alliance troops in Firefly, only turned upside down.
- In 2012 after the Free Syrian Army captured 70 year-old World War 2 surplus stocks of German Sturmgewehr 44 assault rifles they started turning up in various rebel videos.
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