CYMA Sport Complete Ver II Gearbox w/ Quick Change Spring for M4 Series Airsoft AEG (Type: Rear Wired / High Speed Motor)

"i only ever buy these gearboxes for the shell and the quick change capability, because it's some of the best i've seen.
the gearbox itself needs a LOT of work to run reliably. the mosfet is trash, the motor is trash, the shimming is trash, the grease is trash, and the lack of aoe correction on the full polymer piston is trash. oh yeah, and the piston itself is trash, and the piston head has a stupid screw that's unlike any other i've seen. i do like the cylinder though.

complaints aside, this shell is not only great for budget builds but it also has one of the best quick change spring systems i've ever seen. this gearbox is great if you're willing to strip it down and rebuild it, but it's pretty expensive if you're just gonna keep the shell like i do. no where else you can get it though, other than a boneyard gun

"This gearbox with a RHop barrel is unbelievably nasty! 10 out of 10 I switched my stock gearbox with this one and used a 6.02 tight bore barrel and went up on BB weight between.30-.36 and it’s sending it every time definitely would recommend to buy!

"very nice GB, it actually come with a full cylinder, rear wiring with deans, plenty of length. I slapped it in my cyma M16a1 as it was the previous gen without these internals, I had to shave down the full stock mounting screw by about 1/8" for proper fit. other than that its shooting 1.4J consistently, 330 fps with .28s and about 20rps on the motor. Ill be buying a second one of these.