Thank you everyone for the replies, incredibly helpful.
I removed the recoil slider as it kept jamming the piston, especially after full auto use. I don't know if the whole gearbox was replaced including the MOSFET (I have a picture of the writing on the MOSFET if that would help to Identify the Gearbox make). Now going to see what ratio of gears it has as I have already had it apart a couple of times and did not see on the gears what they were, all though I was never looking for it.
Any ideas as to what ratio it might be? 16:1 or 13:1? It does shoot quickly on full auto and is faster than my stock Double Bells PDW.
Thanks again all
Simon