Bolt, Bolt Carrier, Recoil Spring, Spring Button, Dust Cover, and Magazine have been removed.
It's functional?? Or why the spring?
It's not necessarily "functional," but the spring can be used to push the bolt carrier forward and keep the spring pushing the spring guide/cover button back, securing the dust cover.
ohh I see, in the AR V4 are you going to include springs to?
In the end, it's the builder's decision. As far as the design, however, I haven't attempted to make room for them yet, but it'll probably be necessary.