WHAT DOES SMOKELESS POWDER MEAN?

I will get conversion cylinders for all of them in .45LC, however the 1858 can even be .38SPL as well as the 1851 .38LC. Since my rifle is .38SPL I'd personally ideally want the pistols for being in precisely the same cartridge, on the other hand I do not necessarily want to own two 1858s and according to my research I am not precisely chomping wit