The RetroArms CNC Gearbox M249/PKM (8mm) – QSC is a CNC gearbox designed for M249 and PKM airsoft replicas, machined from a single block of aircraft-grade EN AW 7075 T651 aluminum and clearly labeled by the manufacturer as an airsoft part, not for real gun. The build focuses on rigidity, machining precision, and durability beyond conventional zinc-aluminum shells.

The 8mm version refers to the bushing/bearing seat diameter. RetroArms also highlights several practical improvements: spring holders with anti-jump grooves, bearing seats with reduced tolerance to prevent rotation, formed threads for better strength, centering grooves between the two halves, a dedicated groove for the anti-reversal latch spring, and lightened outer edges in non-critical areas.

The QSC system allows the spring guide to be removed with a hex key, making spring changes possible without fully opening the gearbox. The official page also notes that the spring guide must be secured with the correct screw depending on the replica; on folding-stock or stockless setups, the dedicated QSC screw may be required, otherwise the spring guide can get stuck with the spring.

Technical features

• Model: CNC Gearbox M249/PKM (8mm) – QSC.
• Item No.: 6390.
• EAN: 8596308063905.
• Material: EN AW 7075 T651.
• Version: 8mm.
• System: Quick Spring Change (QSC).
• Weight: 253 g.
• Warranty: 24 months.
• Compatibility: M249 and PKM airsoft replicas with Tokyo Marui-compatible standards.
• Finish: protective anodizing.

Package contents

• 1 CNC Gearbox M249/PKM (8mm) – QSC.
• Screw set.

How to use

• Install only on replicas compatible with the Tokyo Marui standard.
• Use only compatible internal parts and never force the assembly.
• Tighten screws to a maximum of 1 Nm.
• With the QSC system, secure the spring guide correctly according to the replica setup to avoid jams.
• Do not use a MAXX cylinder head.

Safety warnings

• Intended only for airsoft, not for real firearms.
• Do not tamper with, modify, or force the product.
• Do not exceed the recommended screw torque.
• Always verify correct spring guide retention and centering of the gearbox halves.
• Keep out of reach of children.
• Installation requires technical skill; incorrect assembly can damage the mechanism.
• Stronger springs reduce system durability.

The RetroArms CNC Gearbox M249/PKM QSC is a premium base for serious custom builds, offering a very robust shell, precise machining, and faster maintenance than a traditional gearbox.