Bull Craft M240 HPA Gearbox Shell

Drop the dead weight. Keep the firepower.

The Bull Craft M240 HPA Gearbox Shell was engineered from the ground up as a purpose-built lightweight replacement for bulky stock gearbox systems. While the factory gearbox weighs approximately 1 lb 9 oz, the Bull Craft gearbox with a PolarStar engine installed weighs in at only 8 oz — dramatically reducing weight while improving alignment, wire management, and overall install simplicity.

Designed specifically for PolarStar and Wolverine HPA engine configurations, this gearbox uses an M249 nozzle setup and was built with ample room for wiring, FCU routing, and clean internal organization without the cramped headaches of traditional conversions.

No shims. No fighting alignment. No guessing.

Just a clean, lightweight HPA conversion built the way it should have been from the start.

🔥 Built Different. Built Bull Craft.

Optional Add-On

✔ Extended 14" Grip Line Upgrade

The standard grip line measures approximately 10 inches, positioning the air adapter directly near the buffer tube area.

For builders wanting additional adjustment room, we also offer a 14-inch grip line option. Simply cut the line to your desired length, install your air fitting, and you’re ready to go.

Complete PolarStar Conversion Kit Available

For customers performing a full HPA conversion, Bull Craft also offers a complete PolarStar setup package including:

✔ Bull Craft Gearbox Shell
✔ PolarStar Plug Board
✔ Trigger Switch
✔ JST Wire

Everything needed for a cleaner, simpler conversion setup.

✅ Core Features

✔ Ultra-Lightweight Design — Only 8 oz with PolarStar engine installed
✔ Massive Weight Reduction vs Stock Gearbox
✔ Compatible with Wolverine Engine Configurations
✔ No Shim Kit Required for engine installation
✔ Spacious Wire Routing
✔ Uses M249 Nozzle Configuration
✔ SLS Nylon PA12 Construction
✔ Made in the USA

Bull Craft...Built Better.