in fact, if the gap is around 0,1 mm or 004", it MUST work with BLACK POWDER. It is still a tight gap....many SW´s and COLTS of modern manufacturing are around 0,15 mm or 006"like my outdoorsman in brand new condition or my Diamondback or some modern SAA´s.
as a matter of fact, I shoot only BP in my 1873´s, and with a right gap, the revolver must shoot many rounds, at least 4 or 5 cylinders, before giving any trouble, even with the dirties BP.
i did correct the gap problem in my Taurus as just 1 or 2 shots would drag the cylinder, and if the gap is tight, is more a problem or dillatation (in a 1873) than fouling.
so any time we encounter this problem in a revolver, 99% or possiblites that it is a too tigh gap or cylinder touching barrel in some point which is quite common in open tops.
filing must be done with care, with a medium/fine file, not a coarse one.
this TAURUS as i said gave me exactly the same troubles with cylinder rotation......now, with a gap UNDER INDUSTRY STANDARDS, of around 004, after some careful filing, you can shoot almost all day BP loads...and i insist, the gap is smaller than most brand new SW´s.
The picture was taken first time i shot it...the gun shot terribly high as i came from the previous owner but the last four shots were a lot closer..
at 25 meters, one hand and 230 grain bullet with 23 grains of 3F black powder...more or less, aceptable accuracy. Not great but ok.
i now longer shoot this gun, i decided to give it "collector status", as it is one of the very few in EUROPE. Common in USA, hard to find here.
all the best