Actually I remember a gif somewhere that showed the mechbox and it's workings and such. I'll see if I can dig up a link. It basically showed the gear movement, pulling the spring back and such. I believe there was also one for GBB's too (just a diagram of the gas propelling the BB).
Anyone else know the link I'm talking about???
It looked similar to this one except animated.
EDIT: Yep.... Like that video posted... I didn't bother to actually watch the video, I only read the replies.