I'm sure there are different methods, but I've had one gunsmith tell me he doesn't remove barrels from action and another tell me the barrel must be removed for concentric to the bore threads. After threading he screws the barrel back on and it doesn't need to be headspaced (Remington 700) because it threads on to a shoulder. I realize not all gunsmiths are created equal, and some of the different methods may have to do with available equipment, but how can a guy figure this out?