jls:
I have not experienced that problem. In fact, I have not had any blisters from my Rohrbaugh. I did once develop a blister on the front pad of my trigger finger while running a few boxes of ammo through my NAA Guardian .32. However, I was not accustomed to a DAO trigger then, having been carrying only single-action pistols prior to that time. Since that time, I have not experienced the problem with the other DAO pistols I have acquired -- Seecamp .32, Guardian .380, or Rohrbaugh 9mm.
Perhaps you might alter your grip to avoid placing as much pressure on the ring finger.