I've done an Encore barrel using an action truing jig , not the best idea but doable if you lake light cuts.
I've also seen a bushing made than barely slip fits into the bore of the chuck and has a center hold bored to fit the muzzel end of the barrel very snug , assuming that the bore is perfectly concentric with the OD of the barrel I can see this working as the hole bored in the bushing is cut the same time the OD of the bushing is cut.
If sombody had told me that this was a good way to do it , I'd have laughed , but i have seen a VERY well respected builder use this method for ALL the barrels he chambers including record setting match rifles and he has a 3/8" guarntee with his rifles chambered in the non mag calibers. I now another guy that most likely using this method also , maybe he'll chime in