I echo the jug of soapy water at the range for my BP brass, but I also have a Lee handpress with a universal de-capping die to decap also, so the primer pocket gets hit with the soapy water solution. This holds them until I get home for a good cleaning in hot, soapy water, rinse in hot water and the leave upside down to drain and dry. To get the rifle home, I have been just "cleaning" the bbl with regular Hoppes #9 & scrubbing the bore with several patches 'til it "looks" clean until I can get it home for a regular cleaning. A solution of equal parts of 1) rubbing alcohol 2) hydrogen peroxide 3) Murphy's Oil soap make for a real good BP cleaner....a dirty bbl can be Clean in as little as 6-8 patches soaked in it. Good for cleaning your hands too or on minor cuts....maybe, kinda like Balistol as ordered by the Kaiser!
I vote for REAL Black Powder & I use Fed 215M primers, plus I also enlarge the flash hole a bit to make ignition easier, can't 'member just now what size drill but it is a letter drill. CAUTION: if you enlarge the flash hole for your BP loads DO NOT use this same brass for smokeless powder loads!
I have heard that some guys use the duplex loading for better ignition of the BP and to keep the bbl cleaner. I cannot vouch for either as I have never used the duplex loadings.