this is my configuration:
1. ra-tech inner barrel (more precise shot)
2. ra-tech metal rail (plastic rail is too soft)
u have stated that 發現彈道到20米後開始偏
i believe the main reason is the hop up, the hole for the hop up dial on the plastic rail will make a bigger hole after some adjusting on hop up dial
which causes the hop up dial to shift left or right instead pf remaining in the center
p.s. there is no need to change hop up rubber, the orginal one has a very good design