Three drams black powder is a sweet little love tap with the ounce roundball. Ross isn't steering you wrong.
You have absolutely nothing to lose in rolling a few up and blasting them down range. Do it over a chronograph and let us know what velocity you're getting.
Take a look at this photo.
What you see there is what I do with over powder cards, and how I prepare felt wads for blackpowder/roundball.
See that roundball in the tweezers? It's sitting on two felt wads. The one in the middle has a hole cut in it's 'bullseye', it's essentially shaped like a donut. See how it spreads out under the pressure of the ball and the lower wad? That's what you want. See the card in the knurled ring? It's been formed that way via a push through the die on the left. I pushed it through there with the brass punch. That cup-card sits on the powder with the cup opening facing the powder. The combination of that card and the stack of wads does very well to give you good gas seal, while keeping the roundball concentric on it's way to the rifled choke.
Give that a try. Use milk carton for your cards, saddle felt (or circle fly wads, or whatever for the hard felt stock) and normal arch punches like what you see there (get them at the hardware store or make them from tubing that you can get at the hardware store...) to make the cards and wads. You can accomplish the 'cupping' manouver via a block of plywood with a hole drilled in it, and a wooden dowel as a punch.
Grease your felt wads with Crisco if you don't have black powder bullet lube.