Shooting update: Although the weather hasn't exactly been balmy, it was good enough to test the bore sized RB (Tanner mould) @ 25 yd. These are the combinations I tried:
Greased felt OP wad + bare "as cast" .618" RB + OS card: These shot low initially, but upping the powder charge to 80gr. FFFg, improved things, but the group was somewhat to the right of center/hold. This one bears repeating.
Greased felt OP wad + roughened .618" RB + OS card These grouped almost as well as the above, but centered on the target. Same powder charge.
Greased felt OP wad + roughened .618" RB, but no OS card: Same powder charge. Very promising and worth revisiting.
Greased felt wad + "as cast" .618" RB, but no OS card: Large dispersion on the 25 yd. target; not worth repeating. Same powder charge.
Btw, I swabbed the bore after each shot so that I could seat the bore diameter RB without undue effort. It certainly helped as I encountered little difficulty on that score, but I can't say if it had any effect on accuracy. Lastly, the best of these test loads came close to, but didn't exceed the groups I obtained from a smaller, i.e., .598" - .603", patched RB (Lee Precision & Tanner moulds cast ~.598"; my Lyman casts ~.603").