Sorry for the long response time Blair, just got back from at trip to Berlin. I've got an old Brown Bess in my possession. The exterior is covered in very rough file marks travelling from breech to muzzle, obviously the exterior is round. I'm guessing with military muskets of that time period they just filed them by hand? Or were some ground on large drums like the ones in the pictures posted above? What were those drums made of? Are they stone or just abrasive covered wooden drums or similar?