I have never had "ball creep", at least not in my ROA. I load 40-45 grs FFFG with Bore Butter or Crisco over the top of the ball. Once or twice, in my Walker, the ball was sucked back out when the rammer was removed - this was due to too much lube and too deep of a bevel in the tip of the rammer.
The bevel at the chamber mouths is called chamfer. Sam Colt devised it as a way to deflect the gasses from the firing chamber away from the adjacent ones.
You cannot test, or push, the limits of a ROA with black powder.
Like I said before, in my opinion (and several others that I've read) the ROA's design is very similiar to the Rogers & Spencer in it's feel, hammer cock, etc.
Great gun. Great shooter. Best built BP revolver ever made. But due to it's several small springs and parts, I don't think it would have been very popular back in the day.