[Corleone]

Friend of mine had the same problem on his VFC HK 416, and couldn't figure out why he had such a low FPS. He had just replaced his stock spring with a new 1J one, but it would only give him about +-280 FPS. I had him do the timings differently (correctly), and he got 330+ You should try and check this. I know some people don't believe in timing of gears, and some supposedly even proved that gears reset themselves, but this is not the case with any of my 3 gearboxes or my friend's one. You see, it's all about when the nozzle is let forward into it's foremost position and seals up with the hop-up rubber sleeve. At the same moment the piston is released and it starts moving air. Well this is what's supposed to happen, and it didn't happen on my friend's v2 gearbox, or my own v6, without proper timing that is!

Also, for or better airseal between hop-up rubber and the nozzle, get an o-ring (of the proper size) and thread it over the inner barrel, all the way to the hop-up unit. It might be a tight fit, so don't use too thick an o-ring! This will help press the hop-up unit more tightly towards the gearbox, hence giving you a better airseal between nozzle and hop-up rubber.

EDIT: Guys, I'm pretty sure he didn't say anything about swapping inner barrel or cylinder, only the spring. This would mean that the porting should be ok. As long as the spring is placed the right way around, it should be ok. That's if it's an irregular pitch spring!