Grey Birch’s Grass Rat is a versatile firearm designed for light weight, accuracy, and adaptability. It features a unique upper receiver with a free-floating bolt, a pinch system for barrel stability, and a rotatable Pic rail for adjustable elevation. It utilizes AR-15 trigger systems and supports three different calibers with interchangeable parts.
Built from the ground up with four objectives: light weight, interchangeability, accuracy, adaptability. Nothing on the Grass Rat exists for any other reason. At the center of the Grass Rat is an upper receiver built around a bolt that rides on two precision-ground stainless steel rods. The bolt is fully free-floated — it never contacts the receiver. The result is a consistent, low-friction cycle that isn’t fighting machining tolerances or fouling in a bearing surface.
The barrel is secured by a pinch system that holds it concentric to the receiver. Swap barrels in the field and return to zero — dependably, repeatably, without a trip back to the bench. An industry first at the top rail. The Pic rail rotates 180 degrees to move between 20 MOA and 40 MOA. No shims, no swapping mounts, no second rail in your pack. Rotate it, torque it, and keep shooting at distance.
The lower receiver houses the trigger controls and accepts AR-15 pattern triggers and selectors, which opens the widest possible field of aftermarket options — run whatever you already trust. That same lower is also compatible with our .17 HMR and .22 WMR upper receiver groups, so one lower carries you across three chamberings. The Grass Rat is compatible with every Grey Birch stock and fore-end offering.
SPECIFICATIONS:
via Grey Birch MFG
- ACTION: GR Upper
- TRIGGER GROUP: MIL SPEC AR15
- SELECTOR: AR15
- STOCK: GB Folding Stock
- BARREL: 12.5″ Carbon / Stainless
- TWIST: 1:15
- MUZZLE: 1/2-28 Threaded
- WEIGHT: 4 lb 9 oz
- OVERALL LENGTH: 30 1/4″
- FOLDED LENGTH: 21 1/2″
- LENGTH OF PULL: 13″ – 14 1/2″
Learn more about Grey Birch: https://gbmfg.co/