Hi Molly dodger, You can always do it the shade tree gunsmiths way, use the lathe to cut a chamfer or radius on the end of a (short!) steel rod. Then using a small drill, coat the end of the barrel, or tool, with lapping compound and holding the drill and tooling you just made straight off the end of the barrel, slowly and lightly resurface/recut the crown! It only takes a little and you can track your concentricity by the polish marks and depth...
If you decide to go the lathe route, you will need a boring bar to cut the taper for the aluminum barrel sleeves... It would only need an inch plus to hold for that type of job... you could probably modify a tool to bore with in that short of distance...Good luck, til...lat'r....GT
