I was taught option 2 in gunsmithing school at TSJC. I would make a mandrel and true up the face before barreling myself. I know of an excellent rifle builder who uses option 3.
55 degree threads?
The threads are 55 degree form. I measured them by taking a silly putty impress and then comparing the form against a cutter of similar form. Then to make sure I cut a test stub which fits wonderfully well.
After done I smoked the end of the receive and screwed up the stub hand tight. I got at least 270 degrees of impression on the face. I did not "blueprint" or true the front of the action. ie: option 1. And last, I decided the engineers at Steyr designed the gun to only interface with the receiver face so that is good enough for me. Its kind of like following the science.
