First thing, wash your bucking in warm mild soapy water.
Second thing spray some watered down simple green down your barrel and wipe dry. Then if you want to get even more serious spray some isopropyl alcohol down the barrel and wipe dry with a lint free cleaning rag (or my trick which is to use coffee filters since they don't leave lint behind). Isopropyl is also used as an electronics cleaner and will dissolve any remaining oils as well as evaporate out quickly afterwards.
Third, re-seat ALL THE THINGS! Honestly I've seen situations before where you install something (and it looks good), get crap results, take it down and re-seat everything and it magically starts to work better. Take your barrel assy. all down to the base components (hop up unit, bucking, barrel, spacer, etc.) No need to disassemble the hop up assy. but at least make sure it's functioning and the arm moves when you turn the dial and all that. After that put the bucking on the barrel making sure the "line" on the bucking lines up with the line on the bottom of the barrel and put it all back together.
Also I haven't used the KWA 2GX but I do believe it's somewhat popular-ish in the states but IMO you could probably get better for the same price like a Guarder Black, Prommy Purp, or whatever.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE