Bull Craft M249 / MK46 HPA Gearbox

A purpose-built HPA gearbox designed specifically for the M249 and MK46 platform.

Traditional M249 gearboxes are heavy, bulky, and were never designed around HPA engines. The Bull Craft M249 / MK46 HPA Gearbox was engineered from the ground up as an HPA-specific solution, delivering substantial weight savings, improved engine alignment, and simplified maintenance.

The complete gearbox with a PolarStar engine installed weighs approximately 10 ounces, compared to a fully assembled OEM gearbox at approximately 2 lbs. 3 oz. The gearbox shell itself weighs only 3 ounces.

Designed with both performance and serviceability in mind, the engine sits securely inside the shell for precise nozzle alignment and consistent feeding performance. Dedicated mounting provisions for the FCU plug board ensure proper placement without the need for custom mounting solutions.

The shortened gearbox design creates additional room inside the receiver, allowing an 11.1V 1000mAh stick battery and FCU to fit neatly within the gun.

Features

• Purpose-Built HPA-Specific M249 / MK46 Gearbox Design
• Significant Weight Reduction Compared to OEM Gearbox
• Approximately 10 oz Fully Assembled with PolarStar Engine Installed
• Lightweight 3 oz Gearbox Shell
• Secure Engine Mounting for Consistent Nozzle Alignment
• Dedicated FCU Plug Board Mounting Location
• Shortened Design Creates Space for Battery and FCU Inside Receiver
• Front Maintenance Access for Engine Service
• Rear Maintenance Access for Electronics and Plug Board Service
• Eliminates Common Alignment Issues Found with Converted Gearboxes
• Compatible with Polymer and Full Metal M249 / MK46 Platforms

Installation Notes

• Uses PolarStar #3 M249 Nozzle
• Compatible with PolarStar HPA Engine Systems
• Designed for M249 and MK46 Platforms
• Fits Both Polymer and Full Metal Receivers

Additional Information

The demonstration video below was filmed using the stock hop-up unit, a 310mm inner barrel, a Maple Leaf bucking and Bull Craft M249 nutsack mag insert.

Note: Some photos may show markings referencing M60 and PKM fitment. Production M249 / MK46 gearboxes will not include those markings. Updated product photos are coming soon.