I bought a snail capper for my 44Pietta Texan (my first cap and ball gun) from the biggest BP supply place in Australia. It doesn't go anywhere fitting any revolver I have ever seen. I have a straight line capper, which is a pain and caps fall out al the time ($13.50 a 100 down here! I don't cap off, I use a pipe cleaner and some alcohol at home and a dry pipe cleaner at the range, ($1.62 to cap off two revolvers).
As to seating caps, the best ones I have seen are cartridges with a dowel fitted into it and a loop. The guys who ise these usually walk to the loading table with the loop around their wrist, cap teh chambers and then use the dowel to push them on.