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

ID: 33549 (GB-M4-MOS8mm-F)
JG / ASP / GE33549
4.3 stars, based on 3 reviews
JG / CYMA 8mm Reinforced Gearbox for M4 M16 Series Airsoft AEG w/ MOSFET - Front Wired
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Sorry, this item is Discontinued

The JG MOSFET Enhanced 8mm Gearbox is a high performance and high quality release from JG / 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 JG 8mm Gearbox.


  • Wired to the front
  • Integral MOSFET
  • 8mm metal bearings
  • Ball bearing metal spring guide
  • Reinforced piston & piston head
  • Reinforced JG 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: JG / CYMA

California residents click here for Proposition 65 warning

About JG / ASP / GE

JG / Jing Gong (China) / ASP (Hong Kong) is among the world's largest Airsoft OEM (Original Equipment Manufacturer) and pioneer for high quality Airsoft AEG rifles. With superb production capability, volume, and their close relationship positioned JG to provide the world market with great reliable products.

3 Customer Reviews

(Write a review)

by Trevor W. on 06/29/2014
"Gearbox is pretty okay, but the mosfet is poop. The mosfet blew out after i plugged in my 11.1v 20c lipo battery. As for the internals, they're pretty decent. Mine came JAM-PACKED with lube. There was literally enough lube for 2 gearboxes inside of it, though strangely they didn't use any of it in the cylinder. As for airseal... it could be better. A lot better. And i purchased mine directly from the evike superstore, so i believe the gearbox had been sitting on the shelf for a year or 2 because the "M130 spring" this thing allegedly has was shorter than my stock M110 spring. As for the shell itself, ive had an m120 in it running at around 15 rps and it's stood up fine. I've had the thing for about 3 months now and the only sign of wear it's showing is on the paint outside. Now as for the individual parts, Here ya go:
*M130 spring (or at least thats what it should be) - great
*Reinforced 18:1 gearset (my spur gear recently stripped because of a jam :'() - great
*Polycarbonate piston head with small o-ring (had a poor airseal) - sufficiennt
*Polycarbonate piston with metal tooth strip (just the last tooth is metal) - standard
*Polycarbonate cylinder head with one o-ring (and an extremely long nozzle) - standard
*Non-ported aluminum (I think) cylinder - great
*Reinforced metal spring guide with ball bearings - excellent
*Clear polycarbonate tappet plate - standard
*Polcarbonate nozzle - standard
*Mosfet (this one was crappy but in most cases a mosfet would make it excellent) - good
*Steel 8mm bushings - great
*Low resistance silver wiring - excellent
*Polycarbonate selector plate w/ copper contacts - good
*Reinforced metal cutoff lever - great
*Reinforced metal shell - great
That's about it, its a decent reinforced gearbox for mid-level airsofters, and definitely go get a Gate mosfet for this is you know how to solder.
by Brad B. on 10/08/2013
"Some of the below review seem outdated mentioning what seem to be JG's older gearbox from 2010. I am sure evike gets these from JG with their orders of guns and these are the gearbox found inside a JG or Echo1 M4 carbine. It has 8mm bushing, my selector plate is black instead of yellow like the image and the mosfet has a nice hard casing to protect it from accidentals.

415 FPS out of the box on my new custom M4 running a stock JG 363mm barrel.

Over all, the item work as expected. Good strong parts and gearbox.
by Ryan G. on 11/12/2011
"This is a good quality, high value mechbox for the price. Out of the box it was shooting 430fps with a standard 363mm barrel and m4 hopup. I swapped the spring with a M120 and it shot 398fps on avg, perfect for outdoor use as most of my fields cap full auto at 400fps.

Upon disassembly, the interior of the box seemed well lubricated - not full of the vaseline type grease seen in some other JG AEGs. I regreased and reshimmed the box before using but coming straight out of the box it looked fine - shimming could have been a bit tighter for lipo use but that is nitpicking. The piston head, cylinder, cylinder head and air nozzle form a tight airseal. Wiring is a decent gauge and can handle the load of a 11.1v lipo no problem.

Mosfet works well, trigger response is excellent with a 11.1v 1300mah PEQ lipo battery. ROF is exceptional, a quick tap of the trigger on auto will give you a double tap. The Mosfet chip is slim ehough to fit under a standard M4 RAS handguard (electrical taped to barrel to keep steady and water resistant) - just run the plug up to a PEQ box.

One potential issue: The control wire for the mosfet chip is very thin and the solder point rather fragile. When installing the wiring be gentle and DO NOT apply pressure/pull to the wiring harness - this applies to when you split the M4 receiver as well. Make sure to give yourself adequate slack.

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This item is Discontinued.