If you removed the outer barrel and hop-up now is a good time slide it back into place and then add the two 2mm hex screws.

If need help with re-assemble of your hop-up go to step 9 of the G&G CM RK47 Airsoft Reassembly guide

Now slide the front of the AEG back on to the rest of the receiver.

Check the holes on the bottom of the gun. Make sure everything is lined up. Once they are aligned take the black 2mm hex screws with the funnel shaped heads and screw them down.