Same here.. Unique smokeless powder in very conservative quantities is what my antique iron gets. I actually undercharge a little bit at first to see how well it goes, then add some more powder on each reload to see if the accuracy gets better (while never exceeding recommended loads, of course).
Personally, I think jacketed bullets and BP are a big no no if you want to keep your antiques in good shape. A cast bullet will never wear out a bore, whereas jacketed ones will strip rifling pretty fast. Hence my recent investment in a lead melter & a variety of molds in order to feed my collection with a healthy diet.