I've only done one, so I took some soft wood, i think it was white pine, cut it the length of my vise jaw, bored a hole the length of it to the smaller size of the barrel taper, sliced it lengthwise, rasped a rough tapir on each half, folded a piece of 220 every around the barrel just above the breech plug, sandwiched my wood over the emery, placed it in the vise and clamped it. it worked.
Robby