I just finished reading a thread over at the TMA forum and this is not the first time I've heard or read of those who have had accidental discharges (chain fire) with a BP revolver, and it HAPPENED FROM PINCHED CAPS THAT FELL OFF THE NIPPLE END of the revolver.
This is a quote from a TMA State Rep. who not only uses a lubed (over the powder) wad, but uses over the ball grease as well.
I believe this accident occured, not from the front of the cylinder(its a tight lead seal, Wonder Wad and grease over the ball) but rather from a cap adjacent to the fired cylinder falling off and lighting that cylnder along with the one the hammer hits. I can't stress enough the use of a proper fitting cap and ball. I once had a .36 cal misfire and the pressure from the cap pushed the loose(my bad) ball into the forcing cone. I don't know why I didn't cock and fire another round, but my guardian angel was looking out for me that day and I took the pistol apart and found the ball in the barrel. Make sure your caps are tight and your head is screwed on straight as with all firearms.
I believe the lesson here is "never say never" and it's ALWAYS better to err on the side of caution.
This is why I will never pinch a cap.
Do it right men,
Black Powder: Not because it is easy, but because it is hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win...