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

ID: 49403 (GB-RA-CNCV2)
Retro Arms49403
4.3 stars, based on 6 reviews
Retro Arms CZ Billet CNC 8mm Ver.2 Gearbox Shell for M4 / M16 Series Airsoft AEG Rifles (Color: Silver)
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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.

California residents click here for Proposition 65 warning

6 Customer Reviews

(Write a review)

by Matthew R. on 09/07/2017
"This is the best gearbox on the market. If you need a no B.S. shell and are willing to spend the money, you will not be disappointed. There are just too many great features on this gearbox to list. I have an entire table covered with just internals, and every single one fits perfectly into this and works flawlessly. If you're not willing to spend the money, Lonex makes nice shells for about 50 bucks.
-Extremely light
-Grooves on tappet return spring notch
-Precise CNC cuts
-Huge range of compatibility
-There's a little shelf for the wires behind where the pinion would go in, makes installation a breeze
-When using Modify ceramics, they lay completely flat to the inside wall

-I installed Modify ceramics into this shell, but with some holes they would fit but others they would not. I measured the diameter of everything with a digital caliper and the bearings measure ~7.98mm on average, and the shell's slots ~7.96mm on average. Its not really a con since it's still very close, but it kills me to have to put super glue on such a beautiful thing.

Overall, don't let that last part turn you away from this. It's still a fantastic shell. P.S. If you like rainbow colors, they have all different colors of these on the Retro ARMS website.
by Jay D. on 08/10/2017
"dropped titan in there with no problem, everything fit in perfect. only issue is standard buffer tube screw does NOT fit. will need a shorter one
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.

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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.