They are much closer to the correct fit than the Italian counterparts. I have over a dozen and all have needed a spacer, .005 to .040. I have made spacers over .125 for Ubertis and Piettas. Uberti supplied raw barrels and cylinders, arbors came from in-house. The wedge slots in both the arbor and barrel lug are a better fit. 2nd and 3rd gens have a much better barrel gap, all I have are with in spec out of the box for me.
The 'correct' way to fix this is to remove the arbor, weld the end, machine to proper fit and reinstall. A labor intensive job. I short cut it. I machine a spacer the needed thickness and loc-tite it in the barrel lug hole. You can drill and tap the end of the arbor, use a shcs and file to fit. I have seen jb weld used.