Okay, i'm not sure about this, but these BBs MIGHT be leaving residue on my hop up rubbers after each shot.
The grouping got quite inconsistant after a while, so I took out the hop up rubber and saw that there were "white" residue(or smeared off plastic) on the little rubber part that pushes down on the BBs. I had to wash it off with kitchen detergent like you clean grease with.
I've tried to smear off these off the BB with my hand but I couldn't(I really don't think these are coated), so I went on to rub these BBs against my hard wood floor. Indeed the plastic started smearing off. Then I tried some Metal tech 0.25g and found that they do not smear off the floor as easily as Madbull BBs(Still smears off after a while though).
I need further testing to prove this, right now it's just a theory, but I don't like the result at all.