Okay will try to explain as best as possible. Have gotten a Yugoslavian rapid fire milled receiver and a original barrel that was in another cut off receiver that came as a kit and the compliant parts. this is a threaded barrel and receiver. When I installed the barrel the headspace is okay although there is a couple thousandth space between the barrel and the receiver. I am looking for the correct solution for the dilemma. If I tighten the barrel down to meet the receiver the sight block and gas block are about a quarter turn from where they should be and the headspace would be over tight. I do have a mill and a lathe although if I trim off the barrel do I have to rechamber and recut the recess in the barrel at the back for the ejector relief. I have not been able to find any other post on this subject If someone could give me a solution it would make my life easier if it were a press fit I would not have any questions thanks