I've always installed bare blanks or pre-threaded and short chambered barrels. A customer brought in a pre-threaded but un-chambered carbon barrel the other day. 99% of the time i chamber through the headstock and dial in off the bore at both ends. I dialed in the blank to thread for a brake in the same fashion and after if was dialed in I measured the off of the portion of the tenon that rests under the recoil lug, its off by several thou. I'm sure the threads are off by this much also. I cant recut the threads and I would think its more important for the chamber to be spot on with the bore. I can re-cut the shoulder on the barrel after dialing in which might help. Any suggestions??