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

"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

"Worked perfect in my cm18 build. I used the prometheus 8mm bearings and they fit like a glove. I had to file one of the corners on the top on the back of the gearbox (buffer tube side) so my charge handle would fit over it when installing the upper (using a krytac aluminum upper and lower). Other then that slight modification and the tedious shimming it went together perfectly.

Parts I used for my build.

Trigger group- Jefftron Leviathan
Bearings- prometheus 8mm
Gears- matrix steel gears
Cylinder- maxx ported
Piston- hellfire
Upper and lower- krytac aluminum.

"Put this in my limited edition vfc m27 with a retro arms j trigger in the matching blue color and it's beautiful. Had my freind who owns a pro shop build it with siegetek gears and a gate titan. Yes go retro arms for a fully built aeg and a great conversation peace ✌

"We installed one of these for a customer, I agree with the first review, and I have to add, if somebody out there is planning to install a Gate Astor, plan to paint the inside of the box flat black. not a big deal, but its soo shiny inside that the single sided boards get all screwy with the light bouncing around. Really should use a Titan or similar, but our customer provided the parts.

"I have this in my VFC mp5, no fitment issues.

We all know how great and strong these gearboxes are so here are some things to note that aren’t as great.

- Was expecting it to come in a box, instead came in a clear plastic bag, kinda lame but didn’t affect the durability on mine
- The holes for the bushings are too small, I tried FLT, Modify, and even Retro Arms but none fit, I had to open the holes up for any to fit
- The screw used to mount the trigger contacts/board isn’t the same size as most gearboxes. Not a huge deal but why?
- The qc spring guide is nice, but the torx head on the back is wayyyy too big, retro arms even sell a screw-in knob for the guide. Again, why?

"The view windows are nice and it overall has a solid build to it, however the spring guide sits very loosely in its channel and for higher powered springs it wiggles out and jams the whole gun when fired repeatedly. not deserving of the 119$ price point in my opinion.