Update:
So the piston is complete crap. The rifle has started slam firing.....
This after about 4 mags maybe....
I have done a lot of mods to try get it to work but what ever I do it lasts a few shots the slam fires again. The Plastic that the piston is made from is very soft and deforms quickly under stress.
No other option but to replace the piston with an after market metal one.
The piston is 104mm long.
I will probably order this piston in the next few days.
http://shop.ehobbyasia.com/action-vs...-rear-end.html