I've done it two ways and the first was the best. I have an early 58 Pietta Remington. After noting the out or round and different diameter cylinder chamber mouths I removed the barrel and machined a bushing that fit through the frame barrel hole very snugly with no slop on the major thread dimeter tops of the frame hole threads. I then made a very close fitting hole through the bushing center for the shank of a .450 dia. chucking reamer. The bushing housed both the reamer blades and it's shank within the portion fit to the barrel frame hole so that all was co-axially lined up. This kept everything in perfect alignment with center of the barrel boar. I then installed the cylinder back in the frame and reamed all six chambers to the same depth. This is about as close as one can get to actually line boring a fresh cylinder, indexed to the bolt notches. I took clean metal all the way around in each chamber so I wound up with jig reamed round holes, indexed to the revolver it lives in.
I had read it could also be done accurately by hand so I used this method the next time. It was not as successful as the first job . I got some chatter going in two of the holes that I don't care for but in the end with a bit of lapping to smooth things up they are round and within a few 10/1000's the same diameter. The finish is not quite as sharp as the one done with the jig bushing but I think it will prove to probably be just as accurate. I won't actually know though until I get out to the range. I did the second one to bring the ball diameter up to the barrels groove diameter.
