New CTW is double feeding every 5th shot

Bit baffled on this one so thought I'd throw this out for some help.

A mate of mine has just purchased a new CTW MX-2 and when in either single or fully auto it will double feed approx. every 5th BB.

I have replaced the O ring in the piston head ( the yellow one), checked that cylinder head is screwed on tightly, ensured the nozzle is tight but still doing it. I have tried several mags that work fine with the other team CTWs so I know its not mags - anybody any ideas??....

It must be the hop unit, but stripped it down and rebuolt it but cant see any issues.....

Said it was a baffler - thanks is adance fellow CTW gods

I assume that the double feed its not in fact a chopped bb? Just to be sure..

You can try changing the upper and lower (not at the same time) - just to narrow it down to half a gun..

Does it backspin on single?

If you fire on single with only the lower, does the sector gear stop in the same position?

I think its a hop issue as I tried the new lower on an older gun and it was fine.

I also tried the cylinder from the 'problem' gun in an old gun and it was fine.

I think I've cured it by smoothing the inside of the hop unit with a dremmel, but I have another new one which is also doing the same thing - perhaps some flaws in the castings????.

I think I'll investigate into getting a better hop unit made that compliments the new nozzles from the UK as then the CTW will be an awesome pice of kit.