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

ID: 49403 (GB-RA-CNCV2)
Retro Arms49403
4.0 stars, based on 4 reviews
Retro Arms CZ Billet CNC 8mm Ver.2 Gearbox Shell for M4 / M16 Series Airsoft AEG Rifles - Black
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$129.00 $99.00

This item is currently Out of Stock Usually restocked within 1-3 weeks.
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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.


  • 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
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
Color: Black

Manufacturer: Retro Arms CZ

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

4 Customer Reviews

(Write a review)

by Robert K. on 05/05/2017
"This gearbox shell is by far the best full sized Version 2 gearbox I have ever worked with. I didn't have to hold anything down when closing it. The anti reversal latch doesn't shift around like some other gearboxes during reassembly. I also dropped a Gate TITAN in here without any modifications whatsoever. Every dimension of this gearbox is perfect.

-Perfect dimensions
-Quick change spring feature
-No modifications needed
-Spring posts are narrow, with indentations to hold the spring in place. You can use thick pliers to install the tappet plate spring.
-Anti reversal latch is secured just enough that you don't have to fiddle with it when closing the other half of the shell.

None. Really. None.
by Taylor P. on 06/04/2016
"Trust me... I REALLY wanted to give this a 5 star review, I wanted to say it was the best gearbox out there. But I can't. From day one I had problems. When It says, "Disclaimer: Please use discretion when installing custom parts as fit and compatibility may vary. Some modification may be required. Professional installation recommended." It should say, " doesn't work with anything." I have had problems with the cylinder, a TM cylinder fitting. The cylinder head pegs are too small which make the assembly wobble. The trigger trolley and contacts won't fit, Semi won't work the spring guide is press fit and can come undone. Some motor grips won't line up. I had the sand down the area for the motor grip to actually fit over. Then the whole shell wouldn't work with itself! literally the two haves never seemed to line up... I wish I had my money back....

It has great features like QD spring guide and large areas for wires. But I'm having problems with it that a 10 buck crappy china shell wouldn't have problems with. For 100-120 bucks I'd say it is MORE than fair so have better fitment with parts. I've tried many brands and all of them didn't work. I really wanted this to work but I can't recommend Retro Arms. Go with a G&P gearbox. I'm glad I didn't buy a m249 shell. I wonder what other problems would occur....
by Ethan W. on 01/23/2015
"Absolutely flawless. That's the only way to describe the quality of this shell. It's expensive as hell, yes, but there is no role that this cannot handle. I am personally running a DSG build in this for now, and I plan to get another one for my next DMR build. Just to measure compatibility, I tested the fit of numerous different manufactures' parts that I had lying around in the gearbox: G&P, Echo1, Lonex, ASG, Systema, Siegetek, BAAL and Matrix. No compatibility issues whatsoever.

CNC aluminum (flawless and smooth inside and out)
Parts compatibility

The ONLY con to this shell is that for whatever reason the screw holes for the cut-off lever and trigger contact assembly is slightly larger than average. I got lucky and while digging through my parts bin I found the gearboxes of some OLD 'Aftermath' AEG's I'd purchased back in 2008 and the screws that held the contacts into the trigger assembly ended up fitting perfectly. You may end up having to find other means to get properly fitting screws.

Overall absolutely great shell. If you can manage the price, it is totally worth it.

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This item is currently Out of Stock. Most out of stock items are restocked within 1-3 weeks. Some items may take longer. Please add this item to your wishlist to keep posted on its availability.