Originally Posted by ShadowNet
If you bought it from Shootsoft, Buy Airsoft, CAS or Velocity Arms, then the upper receiver is Nylon Fibre. Even says so on their websites. Like I said, the nylon fibre isn't cheap plastic. They are extremely tough and feel cold to the touch. I've gotten my hands on both G&Gs from Mach1/007 and Buy Airsoft/Shootsoft. They are very similar, except the upper receivers.
That's strange, because I'm now 100% sure that my upper receiver is metal. The paint on some spots has worn down (charging handle area, inside areas from disassembling), and underneath it's a shiny silver colour. Perhaps the first batch was different?
HUGE EDIT: My gearbox shell is indeed metal, painted black. Sorry for any trouble or confusion caused.