OK, so I started making the barrel for this mortar. Using a drill press, I have created the powder chamber and the bore - no problems. However, the bore is a bit rougher than I'd like; it looks like a brushed metal finish, with fine machine marks around the inner circumferance of the bore. Nothing unusual given the way I drilled it out, but I'm wondering how smooth it needs to be ? I have tried spinning a slotted mandrel with "fine" emery cloth, but the marks are still there. Should I keep going to a mirror finish, or can the design tolerate some minor roughness ? If it matters, the bore is 0.75" and I plan to shoot 0.73" musket balls (which will hopefully be a loose fit). What do you guys think ?