My one and only chain fire happened in a Uberti Pocket Navy using my own cast .375 round balls. A few of these should have been rejected as they had some fairly deep wrinkles. They had somehow made it into my "inspected" supply, it was at the end of my shooting day and I thought "Just a few more shots". I can only assume these imperfect round balls were the cause of the chain fire which thusly happened at the front of the cylinder. Lesson learned, Mea Culpa.