M249 / MK46 / PKM HPA Gearbox Shell

Drop the weight. Simplify the conversion. Built specifically for HPA.

The Bull Craft Industries M249 / MK46 / PKM HPA Gearbox Shell is a purpose-built replacement for the heavy factory AEG gearbox found in compatible M249, MK46, and PKM airsoft platforms.

Instead of modifying, gutting, or working around an AEG gearbox that was never designed for HPA, we engineered this shell specifically around an HPA engine. The result is a significantly lighter, cleaner conversion with secure engine mounting, consistent nozzle alignment, organized electronics placement, and easier access for installation and maintenance.

At approximately 3 oz for the shell alone, this system eliminates a substantial amount of unnecessary weight from your support weapon while providing the structure needed for a proper HPA installation.

Major Weight Reduction

Weight matters on an M249, MK46, or PKM—and the factory gearbox adds a lot of it.

The Bull Craft HPA Gearbox Shell weighs approximately 3 oz.

With a PolarStar engine installed, the complete gearbox assembly weighs approximately 10 oz, compared with approximately 2 lb 3 oz for a fully assembled factory gearbox.

That's more than 1.5 pounds of weight removed from the platform just by replacing the factory gearbox assembly.

Purpose-Built for HPA

This isn't an emptied AEG gearbox.

The HPA engine is securely positioned within the shell to help maintain consistent nozzle alignment and reduce movement that can contribute to feeding and alignment issues.

The shortened gearbox design also creates additional usable space inside compatible receivers. Depending on your configuration, there is enough room to house an 11.1V 1000mAh stick battery and FCU within the available receiver space.

Separate access areas simplify installation and servicing:

• Front Access — HPA engine installation and removal
• Rear Access — electronics and plug-board placement

HPA Engine Compatibility

The Bull Craft HPA Gearbox Shell is not limited to PolarStar engines.

It can be used with compatible HPA engines from other manufacturers as long as an appropriate M249-spec nozzle is available for that engine.

Compatible configurations may include:

• PolarStar
• Wolverine
• Other HPA engines with an available M249-spec nozzle

Compatibility is determined by the engine and nozzle configuration—not simply the engine manufacturer.

If you're unsure whether your engine has an appropriate M249-spec nozzle available, contact us before ordering.

Available Add-Ons

The base product includes the Bull Craft Industries HPA Gearbox Shell only. Nozzle and electronics components can be added when configuring your gearbox.

M249 Nozzle

Optional M249-spec nozzles are available for:

• PolarStar F2
• PolarStar JACK
• No Nozzle

Choose the appropriate nozzle if you're converting an F2 or JACK that does not already have an M249-spec nozzle installed.

The F2 and JACK use different nozzles. Be sure to select the nozzle that matches your engine.

PolarStar Electronics Kit

An optional electronics kit is available for PolarStar conversions and includes:

• PolarStar plug board
• Trigger switch
• JST wire

The gearbox shell includes a dedicated location for the PolarStar plug board, helping keep the electronics organized and securely positioned within the assembly.

The electronics kit does not include an HPA engine, FCU, battery, wiring harness, airline, or air fitting.

The nozzle and electronics kit can be selected independently or together.

Platform Compatibility

Designed for compatible:

• M249 airsoft platforms
• MK46 airsoft platforms
• PKM airsoft platforms
• Polymer receivers
• Full-metal receivers

Fitment can vary between manufacturers and production generations. Minor fitting or adjustment may be required depending on the replica.

Features

✅ Purpose-Built HPA Design — engineered specifically around an HPA engine rather than adapting an AEG gearbox

✅ Massive Weight Reduction — approximately 3 oz for the shell and approximately 10 oz with a PolarStar engine installed

✅ Secure Engine Mounting — maintains consistent engine and nozzle positioning

✅ Multi-Engine Compatibility — supports compatible HPA engines with an available M249-spec nozzle

✅ M249 / MK46 / PKM Compatibility — designed for multiple support-weapon platforms

✅ Optional PolarStar F2 & JACK Nozzles — configure the gearbox for your existing engine

✅ Optional PolarStar Electronics Kit — available with plug board, trigger switch, and JST wire

✅ Dedicated Electronics Placement — integrated location for the PolarStar plug board

✅ Additional Receiver Space — shortened design provides more room for your FCU and battery

✅ Separate Service Access — independent access for the HPA engine and electronics

✅ Polymer & Full-Metal Receiver Compatible

✅ Made in the USA — designed and manufactured by Bull Craft Industries

Specifications

• Shell Weight: Approximately 3 oz
• Approx. Weight with PolarStar Engine: 10 oz
• Factory Gearbox Comparison: Approximately 2 lb 3 oz
• Platforms: M249 / MK46 / PKM
• Engine Type: Compatible HPA engines using an M249-spec nozzle
• Receiver Compatibility: Polymer & full-metal
• Manufactured by: Bull Craft Industries

What's Included

Your order includes:

Bull Craft Industries M249 / MK46 / PKM HPA Gearbox Shell

Plus any nozzle and/or electronics options selected before adding the product to your cart.

An HPA engine, FCU, battery, wiring harness, airline, fittings, regulator, tank, and any other components not specifically selected or listed are not included.

Demonstration Build

Our demonstration build is shown running with:

• Factory hop-up unit
• 310 mm inner barrel
• Maple Leaf bucking
• Bull Craft Industries M249 Nutsack Magazine Insert
• Bull Craft Industries Cattle Drive feed system

Before ordering, confirm that an M249-spec nozzle is available for your HPA engine.

Not sure which nozzle or electronics configuration you need? Contact Bull Craft Industries before ordering and we'll help you determine the correct setup.