Sorry if this is not in the right section of the forums by the way.
So all I can show you is this one video. It explains it all:
https://www.youtube.com/watch?v=_W3roaUXbGA
UPDATE
I forgot to mention the gun specs, my bad.
- DBoy's M4 CQB Non Blowback AEG Full Metal.
- Openable Dust Cover with dummy bolt catch.
- 420+ FPS with Barrel Extension.
- 1/1 Scale High Performance
- Reinforced Gearbox with 7mm Bearings.
It Costs about $280 where I live. With all the tax.
Thanks.