Any idea of what kind of velocity you were getting out of those 6 grain loads?I also used 5gr Unique in my loads under a 200gr HB bullet. It shoots pretty good. I think that the .41 will probably shoot better with black powder because the HB bullet is like a small minie ball and the BP would seal the bore better. I never tried it because I didn't want to have to clean BP residue out of DA revolvers. I carry my .41 Army Special in the woods pretty often so I loaded up a box with 6grs of Unique and they shoot really well, but I think this would be as close to a 'Ruger only' load as you can get with the .41 Colt and should only be used in sound Army Specials and smokeless SAAs, never in 1892s, BP SAAs or especially Thunderers.
I don't have a chronograph but I reckoned it was somewhere in the area of 750-8. It doesn't seem like much but there was a noticeable difference between the 5gr loads.Any idea of what kind of velocity you were getting out of those 6 grain loads?