Slugging is (was?) routinely used in finishing shotgun barrels for repeaters (single barrels). On a tour of the Ithaca factory years ago, I watched a lady operate a machine that forced a rotating lead slug spinning slowly on a shaft (literally, shaped exactly like a rifled slug) back and forth through the barrel the length of the bore. After two passes, she pulled the barrel out of its fixture and inspected it visually. She said the process helped to polish the bore as well as "move" (I assume by swaging) any tiny imperfections left by the 'Roto Forge."
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