CASTING A LEAD LAP. After unbreeching the barrel and cleaning it as well as can be done, I get a hickory rod close to bore diameter and at 1/8” from one end I file a square section 2” long. Below that I file a narrow groove and wrap string around that groove till it acts as a gasket. I slide the whole length of the rod in from the muzzle so the end with the relieved square portion is about even with the muzzle. I hold the barrel upright in my bench vise, heat the top 6” of the barrel to sizzling with a torch and pour molten lead in and top it up. This forms a lap that, after trimming a bit, will follow the rifling.Exactly how do you refresh the rifling? Special tool? Thanks
MAKING CUTTERS. I then make 2 cutters. One is precisely the width of the rifling grooves and about an inch and a quarter long. It is about 1/8” tall and has about 12 hand filed teeth per inch. It is inlet into the lead lap, precisely aligned with one of the ribs on the lap; the ones that slide in the rifling grooves. Opposite that I inlet a cutter for the lands.
CUTTING AND SHIMMING. The cutters which are inlet in the lap are shimmed up in their mortises till level and barely cutting. Paper about 0.0015” is used as shims under the cutters. Then the lubed cutters are drawn through the bore one groove at a time, cleaned of fine shavings (swarf) and drawn through the next groove. Typically 3 passes are made in each groove before it passes without cutting and needing shimming up. Eventually the cutters cut continuously end to end and remove all pits. The bore is then lapped with lapping compound. Usually on a modern barrel, half a caliber is enough. Like from .500 to .505. On an original of my own I’ve gone from .34 to .370. That barrel has about 20 hours in it.
This work is not for the faint hearted or impatient type. These are pix of a set of cutters and lap, very dirty after a job. The lap is beat up and worn from use and running through fine shavings a thousand times. I make no attempt to evenly space the hand filed teeth. All that matters is they are of the same height.