Now she is cycling fine, and there seems to be a good bit of air coming out the barrel.
However she is only shooting 160fps with .2g bb's! Would it be the new piston head? Or the plastic air nozzle looks a little messed up on the inside? Or would it be the hop up chamber? (I took that apart too) :shrug:
(Spring is fine, cycling fine, and sounds the exact same as my other one)
Just test the airleak of nozzle by pushing the piston inside the cylinder, and keeping the nozzle shut with your finger, the issue might be with the nozzle->hopup.
Just google for some mp5k nozzles and see if your nozzle is alright.