A hand-built break-action double-barrel shotgun constructed by the Forge-Smith Collective, a loose guild of independent weapons artisans operating in GLMZ's industrial underbelly. Each Thundermouth is unique — built from reclaimed industrial materials, hand-fitted, and test-fired by the smith who made it. The weapon uses conventional chemical propellant but the barrels are lined with carbon-lattice composite tubing that handles pressures far beyond what traditional steel can manage, allowing massively overcharged loads.

The Old Testament designation is not a model number — it is a cultural label applied to any Thundermouth that has been chambered for the Collective's proprietary 'sermon shells,' oversized 8-gauge cartridges packed with a mix of tungsten bearings and thermite fragments. On firing, the thermite ignites from propellant flash and the shot pattern arrives at the target already burning. The effect at close range is apocalyptic.

The Forge-Smith Collective operates without corporate oversight, patents, or quality standards beyond individual artisan pride. Each weapon bears the maker's mark — a personal sigil stamped into the receiver — and reputation within the Collective is built entirely on the reliability and lethality of the weapons produced. A smith whose weapon fails in the field loses standing that may take years to recover.