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Retro Arms CZ Billet CNC 8mm Ver.2 Gearbox Shell for M4 / M16 Series Airsoft AEG Rifles (Color: Black)

ID: 49403 (GB-RA-CNCV2)
6392 CNC Gearbox Ver. II 8mm
Retro Arms8591884940396392 CNC Gearbox Ver. II 8mm49403
4.0 stars, based on 13 reviews
Retro Arms CZ Billet CNC 8mm Ver.2 Gearbox Shell for M4 / M16 Series Airsoft AEG Rifles (Color: Black)
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Retro Arms


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  • Precision machined from a block of billet EN AW 7075 T651 aluminum
  • Quick change spring guide system
  • Durable anodized finish
  • Reinforcement in key stress points to counter rapid wear from high performance parts
  • Pre-radiused cylinder windows - helps evenly distribute impact force
  • Deeper wire channels along base of gearbox
Unlike most other gearbox shells on the market, the Retro Arms CZ gearbox shells are precision CNC machined out of a solid block of billet EN AW 7075 T651 aluminum giving them unmatched durability and resilience. Combined with reinforcement of key stress points and stainless steel connecting bolts, the gearbox shell has undergone extensive stress tests with M160 springs without any signs of wear.

Version 2 Retro Arms gearboxes feature a quick-change ball-bearing spring guide mechanism, allowing spring swaps in a matter of minutes without complete gearbox disassembly.

Manufacturer: Retro Arms CZ

Color: Black


Compatibility: For Tokyo Marui, G&P, Matrix and other compatible M4 / M16 Series Airsoft AEG Rifles (Modification may be required depending on brand and model)
Material: CNC Billet EN AW 7075 T651 Aluminum

Disclaimer: Please use discretion when installing custom parts as fit and compatibility may vary. Some modification may be required. Professional installation recommended.

13 Customer Reviews

(Write a review)

by Frank H. on 03/19/2021
"Great gearbox. Was everything I thought it would be.

One small problem though: my buffer tube screw was too long for the QC spring guide that came with this gearbox. It was originally M5 x 50mm, had to grind it down to M5 x 40mm for it to fit correctly. Also if you're gonna remove material to fit bushing/bearings, use a hand tool and manually take off a LITTLE bit at a time. Don't go crazy with it!
by Whit M. on 11/18/2020
"These gearboxes are absolutely beautiful and machined very well. FLT bushings fit flush on both sides although they were extremely hard to fit in the shell, I removed some material from the inside of the bushing holes to accommodate. Everything else fit absolutely fine, almost every part in my gearbox is SHS except the cylinder is LCT and the cylinder head is King Arms. This gearbox is extremely light, very strong and easy to use, with extra features making it easier to tech on. Installed a JeffTron Leviathan as a drop-in fit, aftermarket MOSFETs require no modifications to install. Overall great product! I’ll have a video review up on my YouTube channel Octane Airsoft shortly!
by Thomas U. on 07/17/2019
"These Gearboxes from Retro Arms have been a game changer in the teching world. I absolutely love how well these are machined and fit. The fit and finish alone is beautiful and is almost worthy enough just hang on a wall. The level of reinforcement that is in these gearboxes is amazing! I have been running these gearboxes in many different builds and I must say, this is top notch quality

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