So after further tinkering around with this gearbox (CM 02B) I realize that it not only has a pneumatic blow back system but a RECOIL system as well. There is an open hole in the top/back of the gearbox.. i can see the spring from the top of the gearbox.. the Piston looks like it has a groove or section cut out of it as well..
There is a metal arm that is bolted to the gearbox body and attached with a spring to the front receiver'. To separate the two halves i need to unhook this spring.
what the hell did i buy!!.. if i can't tinker with a gun then whats the fun damm it.