weird double/triple feed

[Reckless]

alright... I'm stumped, customer is fed up with the gun.

gun has a random but frequent double and triple feed

customer bought it as a franken gun. it "fired" but it had massive airseal issues, sloppy mag locking, etc

M4-
Noveske/magpul (G&P) upper/lower.
A&K gearbox


now... I have done:

got rid of airleaks (piston/head, hop rubber, nozzle)
put a G&P hop unit in it (matched with nozzle)
changed the spring, reshim
"shimmed" the hop housing to sit against the gearbox (mainly with the spring, it's not rammed up against the gearbox)

when it fires a single round properly it's a wicked gun... it's consistant, range is great.. etc

and then it starts double feeding... tripple feeding... then it'll be normal again... then .. etc

the only thing I can think of is that the nozzle is being pulled to far back, and randomly it's letting more then 1 through? ... cause it's seating forward beautifully


oh and we've tried 6-8 different brands and types of mags.... and it doesn't seem to make a difference.

as I said .. the customers fed up... as am I cause it appears to work in the shop... and then a new problem (now it's the random multi feeding) ...