@ Blobface: Yes you've got it. It was a Blackviper in clear plastic.
The only advantage was the price.
All internal have been changed by standard material (I mean metal, reliable and strong enough to support our hobby): Gearbox, hop-up bloc, hop-up, precision barrell, replacement of plastic parts by metal such as sights (F&R), installation of a red-dot and grenade launcher to add some weight and a paint work (inside and outside).
Now this replica is working fine, the only outstanding issue is the weight feeling in your hands, still on the light side.
I will surely not treat this replica as I do with my LCTs, E&Ls, VFCs or NPOs