ghk m4 gbb box npas?

[bushman]

hey everyone, i was just curious if anybody has put an npas into this system. i am trying to do a dmr build, but i dont want the fps to be outrageous! i will be running a 509mm length barrel for now but that might change down the road. any help is appreciated. the valve that is currentally in it looks like the we m4 vlave.

we m4 npas
http://www.evike.com/product_info.php?products_id=32177

ghk manual, part 5 i believe
https://www.google.com/search?q=ghk+gbb ... 600%3B1200