I just returned from the range after testing "bare," i.e., unpatched RB's in my 20ga. Green River Forge trade gun (flintlock). The particulars will follow in a moment, but the verdict, at least for my gun, is that patched RB's are significantly more accurate than the bare ones, and those results are repeatable.
Today's frolic involved .618" - .619", i.e., bore diameter, weighed RB's (Tanner mould), seated over 80gr. Graf's Schuetzen FFFg + a grease wad. No OP or OS wads were used as those RB's are a tight fit in the bbl. I also swabbed the bore after each shot for loading ease and consistency. In this test, the balls were rolled between 2 coarse files and dipped in melted Crisco + beeswax. From a rest @ 25 yd. I could keep most of the 7 in an 8" bullseye, with some (2) near each other, but not touching.
Test #2 involved RB's cast (and weighed) from the same Tanner mould, but not rasped like the others. These were also fired with 80gr. of Graf's Schuetzen FFFg, but with the addition of a proper OP wad (~1/8" thick), a felt grease wad, and a thin OS wad to hold the unrasped but slightly looser fitting balls on the powder charge. The results? Better than the rasped RB's, but my 7th and last shot (high at 11 o'clock) really opened the group. This one is worth retesting, but it's still not as accurate as a patched RB in my gun.*
*My trade gun will shoot either a .014" or .018" pillow ticking patch + a .598" (Tanner & Lee moulds) or a .603" RB (Lyman mould) quite accurately @