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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
3.8 stars, based on 10 reviews
Retro Arms CZ Billet CNC 8mm Ver.2 Gearbox Shell for M4 / M16 Series Airsoft AEG Rifles (Color: Black)
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Color Options:

Color: Black

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.

10 Customer Reviews

(Write a review)

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
by Johnson P. on 05/26/2019
"Picked mine up at evike on Saturday. The quality is phenomenal, I can’t describe how perfect the dimensions are. Very light compared to stock gearbox. I am using it in my dmr build and hopefully it withstands the m160 it claims to be rated at. Before this my gun shot about 550 fps and the stock gearbox eventually cracked(I knew it would break but at the time this was out of stock). The only problem I have is it fitting the stock Krytac pistol grip. Not a big issue, I was going to replace it anyway. 11 out of 10
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.

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