400fps is to much for that crappy mechbox. Downgrading the spring is a good idea (and metal bushings).
The one i got here is getting a TM mechbox, metal bushing and a systema M100 spring. Systema grease/lub and its good to go.
I think of Jing Gons as mini project guns. Deff worth it once the little bugs have been worked out.
Its true having to take the gun completly apart... sucks! But hey blame TM