I think I had Wild Bunch on my mind when I put on that bit about the Colt hammerless (I will get a thread on what guns to use at Wild Bunch later.). I went looking at
http://www.wvcass.org and they said that the latest they would let you get away with is the 1899 (History tab, all the way to the bottom). So I guess the question is akin to the one about the tootsie pop... the world may never know.