RetroArms CNC Gearbox HPA, V2

Building a no-compromise HPA rifle? The Retro Arms CNC Gearbox HPA V2 (2025) is a benchmark among gearbox shells. Where traditional gearboxes are designed for mechanical gears and pistons, this special version is machined specifically for installing HPA engines (such as PolarStar, Wolverine, Redline or Gate Pulsar).

Machined from a single piece of aircraft aluminium (EN AW 7075 T651)

Retro Arms is known for high build quality, and the 2025 model is no exception:

• Precise HPA alignment: Because the shell is CNC machined to tight tolerances, your HPA engine sits centred every time. This eliminates nozzle alignment problems and gives you a tight air seal, consistent muzzle velocity and high accuracy.
• High durability, low weight: The gearbox is machined from a solid block of EN AW 7075 T651 aircraft aluminium and can withstand the punishment of hard use on the field.
• Optimised HPA design: Unnecessary features for the traditional AEG system (such as gear bearings, piston guides and AOE cut-outs) are omitted or optimised. This leaves plenty of room for your HPA lines and wiring, so you avoid pinched cables.

Easy installation and well-thought-out details

The 2025 version has updated wiring channels and an even sharper finish, so it slides into practically all standard V2 M4/AR15 receivers. The surface is anodised, which protects the aluminium against corrosion and wear.