Mike- I'll try that system you used some day - if I ever run across a barrel that needs it. At this point, my GM .45 shot well right from the start - maybe I was lucky with it. Pulling the plug and looking down it, the grooves and lands are bright and shiny just as if it had been carefully lapped, THEN polished with Flitz or JB - lots of strokes, BUT the corners are sharp and clean of any blemish or imperfection. It even appears better than my Goodioen barrel - inside. The accuracy is slightly better as well - it was never labeled as a MATCH barrel and cost less than 1/2 as much.
I have a .433" mould which will allow a very heavy patch laden with compound, I'm sure, which will scrub even the grooves - guess I'll hang onto it. I have some WW balls cast from it to try with heavy patches to see if they'll shoot OK.
One other method that could be tried, is to load a small charge of powder, say 20gr., then 2 1/10" tight wads, then another wad with a grease/goop of compound stuck to it's base, so the grinding goop is between the wads, then a patched ball to add inertia to the 'load' to slow down the velocity. The compression between the wads should spread the compound out against the bore and the double wads behind would work to run it against the bore, polishing it.
It's easier to use a tight patch on a jab with compound on the patch, even Flitz, and about 20 to 100 or more strokes up and down will effectively polish most bores. Flitz is substancially more aggressive than JB compound and will polish nicely.
Now, a .20 or .17 cal RB rifle - for small vermin? Silk for patches, of course - or 600 tpi cotton. What twist?