Description
Retro Arms CNC Gearbox M249/PKM (8 mm) QSC
The Retro Arms CNC Gearbox M249/PKM is a high-strength gearbox shell designed for compatible M249 and PKM airsoft machine guns. It is CNC-machined from EN AW 7075 T651 aluminium alloy and provides a considerably more precise and robust foundation for demanding support-weapon builds than conventional cast zinc-alloy gearbox shells.
The gearbox features 8 mm bearing seats, a Quick Spring Change system and several construction details designed to improve durability, alignment and ease of assembly.
CNC-machined EN AW 7075 T651 construction
The gearbox is manufactured from EN AW 7075 T651 aircraft-grade aluminium alloy using CNC machining. Retro Arms states a tensile strength of approximately 590 MPa for the material and compares this with approximately 390 MPa for common structural steel.
Unlike conventional cast gearbox shells, the CNC-machined construction allows the gearbox halves and critical internal dimensions to be produced with high precision.
Protective anodized finish
The gearbox features a protective anodized surface that helps protect the 7075 aluminium alloy against corrosion and surface wear.
Quick Spring Change system
The integrated QSC system allows the spring and compatible removable spring guide to be accessed through the rear of the gearbox without opening the gearbox shell.
The spring guide must be properly secured in the replica. Depending on the platform and stock configuration, a separate QSC retaining screw may be required.
8 mm precision bearing seats
The gearbox is designed for 8 mm bushings or bearings. The bearing seats measure approximately 7.98 mm, making them slightly undersized to help prevent the bearings from rotating or moving inside the shell.
The edges of the bearing seats are chamfered to make installation easier.
Improved internal design
- Grooves help retain the tappet plate and trigger switch springs during assembly
- Dedicated groove for the anti-reversal latch spring
- Gearbox halves are aligned using CNC-machined grooves and mating edges
- Critical areas have been redesigned for improved strength while reducing unnecessary material
- Threads are formed for improved strength
- Outer edges are chamfered to remove unnecessary sharp corners
Compatibility
- Compatible M249 AEG platforms
- Compatible PKM AEG platforms
- Designed around Tokyo Marui-compatible internal standards
- Commonly used with CA / A&K-style M249 and PKM configurations
- Designed for 8 mm bearings or bushings
Compatibility may vary between individual manufacturers and models. Parts from different airsoft manufacturers can have dimensional differences, so fitting may be required.
Important installation information
Do not use MAXX MODEL cylinder heads or similar cylinder heads that transfer the piston impact incorrectly to the gearbox shell. The cylinder head locating pins are intended to position the cylinder head and should not absorb the piston impact.
Retro Arms recommends a maximum tightening torque of approximately 1 Nm for the gearbox screws. Excessive tightening can damage the screw heads or threads.
Technical specifications
- Manufacturer: Retro Arms
- Product type: CNC gearbox shell
- Compatibility: M249 / PKM
- Material: EN AW 7075 T651 aluminium alloy
- Manufacturing method: CNC machining
- Bearing size: 8 mm
- Bearing seat diameter: approximately 7.98 mm
- Quick spring change: yes, QSC
- Surface treatment: protective anodizing
- Weight: approximately 253 g
- Product number: 6390
- EAN: 8596308063905
Package contents
- 1 × Retro Arms CNC M249/PKM gearbox shell
- Gearbox screw set
Spring guide, bearings and gearbox internals are not included.
Installation requires experience with AEG gearbox assembly and component fitting.
