CYMA 8mm Reinforced Gearbox for M4 M16 Series Airsoft AEG w/ MOSFET - Rear Wired

4.0 stars, based on 11 reviews


This item is currently Out of Stock

Usually restocked within 1-3 weeks. Add to your wishlist to stay posted!

ID: 33550 (GB-M4-MOS8mm-B)
The manufacturer of this product enforces a strict minimum advertised price (MAP) policy which excludes this product from any additional discount coupon codes. This item, however, may qualify for free shipping.

11 Customer Reviews

by Kenneth L. on 07/28/2015
"I made a previous review about it and I want to write another one for it. I officially had this gearbox for over a year. I had it as a spare gearbox since I "supposedly" got a newer one. Lo and Behold, I fried my new one and switched it back to this one.

From last time I chrono (my last game was in November 2014) it was shooting in between 378-381FPS with .20g. I chronoed sunday (7/26/15) and had the same fps on a M130. My gun is using the Madbull ultimate hopup with a 6.05 inner barrel and I can hit easily about 160ft using .25g. I gave it slightly more hop up and I was able to hit some at 102 yards. EVERYTHING is stock except the trigger contacts due to malfunction.
by Kenneth L. on 08/18/2014
"I got this about 2 weeks now, and had to wait to my upcoming event to have a true test. I was able to hit targets at least 50+ft with confirm hits, debatable around 80ft. Mine came with a ported cylinder shooting at 348fps, which it isnt that bad. However, if you want full power change it to a non-ported cylinder.

MOSFET is COMPLETELY different from the picture and its an APS MOSFET. Since its rear wired, you have to either use a stick battery or use a nun chuck for crane style stocks.

All in all, it performs really good, and I am satisfied with my purchase :D
by Steve J. on 08/06/2014
"I bought this gearbox to replace an old gearbox that had issues.
Taking it out of the box everything looked in order. I dropped it into my KA OA-15 M8 and tested the weapon. The first 10 shots seemed decent, that's where it goes bad. After about the 10th round bb's started flying everywhere, dropping, rising, no consistency whatsoever. 50 Ft shot group was about 15 feet wide. So I checked out my barrel / hopup to see if there was something wrong with the gun, nothing found. So I decided to look further into the new gearbox... I opened it up.

There was rust on the gearbox housing internally.... yup....
Bushings not Bearings
There was enough grease to drown the fonz (old reference?!)
The cylinder had almost no air seal / compression
The Air nozzle and piston had the quality of a cheap model car set.
Horrible Shimming
The spring had no... spring...

So I paid to basically get a set of spare parts, which I was able to use to create a decent gearbox when I cleaned it up, reshimmed, put in a new spring, piston, air nozzle and properly sealed the cylinder.

I gave it a two for two reasons -
First, at least all the parts were there?
Second, the wiring harness and mosfet were in excellent condition.
CYMA 8mm Reinforced Gearbox for M4 M16 Series Airsoft AEG w/ MOSFET - Rear Wired

CYMA 8mm Reinforced Gearbox for M4 M16 Series Airsoft AEG w/ MOSFET - Rear Wired

The CYMA MOSFET Enhanced 8mm Gearbox is a high performance and high quality release from CYMA which has been proven by their release in the popular rifles. Need to replace your gearbox or just looking for something new to upgrade your old AEG? Look no further than the CYMA 8mm Gearbox.


  • Wired to the rear
  • Integral MOSFET
  • 8mm metal bearings
  • Ball bearing metal spring guide
  • Reinforced piston & piston head
  • Reinforced CYMA gear set
  • Reinforced cylinder and cylinder head
  • Low resistance silver wiring
  • Reinforced gearbox shell
  • Velocity output for this gearbox is estimated to 370~460 FPS, depending on inner barrel length, hopup, and associated parts
Compatibility: For Tokyo Marui, JG, CYMA and other compatible M4/M16 Airsoft AEG rifles

Manufacturer: CYMA

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.

Wanna chat about CYMA 8mm Reinforced Gearbox for M4 M16 Series Airsoft AEG w/ MOSFET - Rear Wired?

Have questions about this item? We monitor these comments daily, but it may be faster to email us directly or call us at 1-626-286-0360.

Facebook about THIS with your friends! Comment for a chance to win awesome airsoft prizes. Details can be found on The Evike Facebook Fan Page HERE! Remember to leave "Also post on Facebook" checked to qualify your comment!

Items on Sale