The Graviton Gun is an exotic and unconventional Grav-Weapon used by the Imperium. It is a medium-sized weapon which utilises the gravitic reaction principle most commonly seen powering grav-vehicles such as the Land Speeder. Each gun is a rare relic left over from the Dark Age of Technology and are now sacredly guarded by the Adeptus Mechanicus, and very rarely will they allow one to leave their armouries, but some Space Marine Chapters still field a handful of such weapons.
The weapon fires a stream of particles which affects the local gravitational field of a target area, making the targeted object either far heavier or lighter depending on the weapon's setting. The gun also creates a bass rumble as the waves affect the local air pressure, causing the air to vibrate. The effect is generally non-lethal and can be used to incapacitate foes who need to be captured alive, but the power of the graviton gun's highest settings is sufficient to rupture organs and crack bones even inside armour. Some living targets will be affected more variably; a very large creature may be killed under excessive weight, but most targets will either be slowed or completely immobilised. The graviton gun is very useful when fighting on a star ship or a null gravity enviroment, as well as for for demolition and siege work, as it is most effective against massive objects such as bunkers or fortifications, where the building's great mass can be used against it, causing it to collapse. 
- 1: Warhammer 40,000: Wargear (2nd Edition), [Needs Citation]
- 2: Dark Heresy: The Inquisitor's Handbook, pg. 133
- 3: Rogue Trader Rulebook, pg. 128
- 4: Imperial Armour Volume Nine - The Badab War - Part One, pg. 153
- 5: FW Website Space Marine boarding assault upgrade set (last accessed 11 June 2015)