A large ring barrel wouldn't go near the threads and with measurement it showed to be a small ring thread or so the GS said. It ended up being irrelevant anyway as getting the new barrel made this an accademic question for me. The new 6.5x55 barrel was a large ring but as I had to have a 1/2 inch cut off the chamber end to rechamber for the 6.5x57 it was rethreaded to suit my action.