Could you use a boring bar to make an existing chamber or throat more concentric before running in the finish reamer? I know this would be a delicate operation and my cross slide probably wouldn't handle it on my Sheldon , but a heavier duty lathe might do a clean job of this as long a you're only talking about a light pass on the non-concentric areas?
Barrel blank in the headstock with Deltronic pins in either end. Indicate both ends. Drill and then reach in and indicate the throat. I use a solid carbide boring bar to taper bore to the shoulder. If you indicate the throat and taper bore it, it will be concentric to the bore. Your reamer will now follow the taper bored hole. I use no bushing as I do not want it to influence the direction of the reamer.
