Another "maybe" cause of the misfires could be residue from the 'wet' patch getting into the opening of the nipple. Is that long nipple thread reaching into the bore?
I used to have a Pedersoli "Kentucky" that would always misfire right after the wet patch/dry patch operation, and many times it would take 3 or 4 caps to get the fire channel dried out enough. I switched to both a thicker patch and mink oil lube, and then no further need to clean until I got home. Many times before I switched, I would have to take the bolster and nipple out, and use pipe cleaners to clean out the holes.
Darn shame, cause that .45 was extremely accurate, often making a small clover-leaf in the X-ring at 100 yards, prone position.