Sig 552 not feeding reliably

[axisofoil]

Okay... my project gun... a JG Sig 552.

Version 3 gearbox

When I fire it, the gun cycles... and it sounds like the gun is firing regularly.
However, it will only fire about every 5th-6th time the piston cycles... with the gearbox out, it looks like the nozzle isn't cycling the same number of cycles as the gearbox (i.e. every 5 times the piston fires, the nozzle moves back and forth 3 times) or something like that. It also has a severely lowered fps (160-250 instead of 410 like it used to be) (i suspect this is from the same problem) when it does fire.

Any idea what's going on?

I've tried:
Opening the gearbox, the tappet plate is not damaged, and the sector gear is not damaged.
Changing the piston/piston head/spring
Crying in the corner


Any suggestions, tips, insider information, new ways to threaten the gun into firing?

[yammie r6s]

are you sure about the tappet plate?, if your nozzle isn't moving every time you fire then something is wrong period. either the tappet plate is broken(you say it isn't) or the nozzle is broken (in which case you could pull it sraight off the front without opening the gearbox. i guess it could be possible the cam on the gear isn't doing its job but i've never seen that fail.... check to make sure you still have your return spring that hooks on to the tappet plate

[axisofoil]

Return spring is on
Tappet plate is in one piece
Nozzle isn't broken either.

Maybe the tappet plate is jumping the cam on the gear instead of engaging?

I know that something is wrong... all I can think of is the tappet plate or the nozzle... and they aren't broken.

Another piece of information... this problem seems to be on and off...
I took it apart to clean the gearbox and the problem showed up.
Took the gearbox apart to figure out what was wrong, couldn't find anything, put it back together, it chronoed at 200fps... i checked airseal and replaced the piston/spring with a good-sealing piston and a m110/sp100 (i'm not sure which... that fps range) to see if that was the issue with the 200fps stuff... now it's not feeding again and firing at 200-250fps or so on the rare time that it fires without double-feeding.

[axisofoil]

I noticed that sig 552 nozzles are sold separately from other version 3 nozzles... I think I may have put in a different nozzle than the stock one when I opened it up to shim it...

Could an incorrectly sized nozzle do this?