Grav-Gun

Graviton Guns are ancient and devastating weapons based on ancient and forgotten technology. Manipulating the very nature of gravity itself, the gun turns a target's mass against it, crushing it to pulp under its own weight. This is especially shocking when used against heavily armoured infantry like Terminators, the hapless warrior brutally crushed by the bulk of their ceramite plates until only a crimson trickle remains of what they once were. Space Marine Chapters are among the few warriors of the Imperium to be gifted with the use of grav-guns, and it is a sacred honour for such a potent weapon.

History
The secrets of grav-weapon construction are known only to a precious few; their design is based upon the graviton weaponry many Space Marine Legions employed during the Horus Heresy era in the early 31st Millennium. Even then, these exotic and rare weapons were little understood by the Tech-prists of Mars. The term "graviton-gun" refers to a group of gravity projector devices whose sophistication is such that the few that remained were relics of a lost age. These weapons proved extremely useful when fighting on a starship or in a null gravity environment. The power of the graviton gun's highest settings was sufficient to rupture organs and crack bones even inside armour, but its primary use was to impede the enemy and damage machinery without the risks of secondary explosions.

But these secrets are still locked away in the deepest vaults on Mars. Only Techmarines who show the greatest promise are entrusted with the sacred binary psalms detailing the assembly and maintenance of such weapons. In battle, grav-weaponry affects the local gravity field, using its victim's own mass against them, an ordeal that will stun those it does not kill outright. Heavily armoured targets find themselves crushed as if by the mighty fist of the Emperor himself, while vehicles are left as crumpled, smoke belching wrecks.