Emory cloth wrapped around a dowel rod comes to mind. There may be a reason most fluted barrels are bead blast finished. Depends on how badly you want polished flutes.
if i were inclined i would use bullet shaped points. either in felt or cratex on my dremel tool. on the felt tips i would use successively finer clovers abrasive and keep at it till i got the desired polish.
if a gunsmith shop did it they could use the mill they used to cut the flutes and insert the mandrels in like a cutting burr. that would keep the tool from jumping track and messing up the rest of the barrel.
blasting the barrel or a baked laquer finish first on the barrel abd polishing the fluted would give it a different hue too.
just food for thought. Greg Moyer
They have a nice finis...I saw a polished flute,I liked it.The barrel I saw was flutes,High Polished,rest barrel..well not polished just smooth
Thanks-
My brother-in-law just finished polishing some flutes on a heavily fluted barrel. He took a thin piece of wood and sanded an appropriate radius along one side. Then Kroil and sandpaper on the wood and lots of elbow grease. Turned out very nice.