I wrote an article on the .43 Spanish a few years ago, based on my experiences. I initially had problems with severe case stretch and separation, caused by using 0.072" thick rims in a 0.090" rim recess-the equivalent of 0.018" headspace, which is definitely excessive. I solved the problem in a temporary way, and subsequently Dave Gullo modified my cases to have ~0.090" thick rims, which he now offers in .43 and .43 basic brass. I found the cartridge easy to load with black powder and accurate with the Lyman bullet (haven't tried the RCBS).
I'll e-mail a copy of the article to anyone who posts a private message to me with your e-mail address.
I have an unfired 1879 Argentine as it came from arsenal refit, with new barrel, almost commercial-quality blue, good wood. I don't have the heart to fire it-will probably keep it as a collector and eventually sell it.
Clarence