Perhaps a burr or diameter problem at the mouth of the chambers. I have a ROA that had that problem, after seating a ball, it was loose. I sent it to Ruger and they (not very neatly) reamed the mouths of the chambers with a scraper, which I could have done myself, more cleanly, I might add. I expected a new cylinder.... As someone above suggested, measure the chambers for taper.
Also, I have found that Hornady balls are not as round as Speer. I use 454 and 457 Speer balls in my Uberti revolvers, and some are loose with 454's. Thinking of reaming to 29/64 (.453) which is a close match to the bore grooves. That would demand a 457 ball, I would think.
Seating a 454 or 457 ball in the existing chamber cuts a ring, but the resulting ball is the diameter of the chamber, still quite smaller than the bore. Those who have reamed state an improvement in accuracy.