I've took pictures. And found the problem at the same time.
Hectic is really close.
while thightening the hop up, the bucking slip by like 1mm and was blocking a little little the hole where the bbs come from. and since there is not much force apply to them at this place, they were not able to go through.
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20160415_225350.jpg
see the small red portion blocking the hole? thats the problem. So, I hope this can eventually help somebody else. and thanks for the help.