The procedure of reassembling the gun is the exact reverse of disassemling it.
Replace the chamber release button and place the spring back ontop of it
Screw back in the big rotating mechanism followed by the trigger (The trigger spring connects onto the nearest peg within the shell and the other end will latch onto a hook on the trigger. This was a problem for me but eventually i figured it out)
Replace the spring at the top, place the catch back into place (be mindful of the spring) then insert the plunger with spring connected back into the catch
Add the chamber and barrel back into place
Find the half of the cocking mechanism that has a metal pin on it and place it so that it is through the internal spring at the top but remains outside the shell.
Screw the top half of the body back together and match up the two halves of the cocking mechanism, replace the spring loaded tactical rail attachment. screw together