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

"Put this gearbox for a 30 RPS 300fps build with the Leviathan trigger and I have to say I'm very impressed with this gearbox and could be the best gearbox shell I've ever seen and used!
It's extremely light, very solidly built, and comes with everything you need to build it. The one thing that stands out a lot, is there's a groove for the wires that go under the motor, rarely do I see something like this in a gearbox and this makes it so the wires don't get entangled with your motor. A very nice addition and very necessary for high speed builds. The AOE window for the sector gear and piston, is also a nice plus. Lastly, the weight, it is ridiculously light and when you finish your gun there is a difference in feel, not significant, but a difference nonetheless.
Ran 250rnd midcap full auto straight, no stops, and the gearbox took no damage.

There are some small caveats though, if you've teched before, is an easy thing to handle. Retro arms own bushings require some sanding on the gearbox holes for them to fit properly. One or two minutes on the Dremel and it solves that issue, no problem. Also, the trigger threads for the screw are not the same as a standard gearbox but they do give you the screw for it. Not sure why they decided to go this route, but as long as I got the screw I'm good.

Excellent product by retro arms. Will buy again!

"This is a great gearbox shell that fits everything I want in it and is finished with superb percision.

"Man this thing is well built. Lots of great viewing windows for shimming and AOE checks. If you're a great builder I'm sure you can use this to do a bang up job unlike myself. 10/10