Like most of you, I have made tools for specific jobs. One that has seen a lot of use is a cutter I made from a 5/16" twist drill bit to re-cut the nose cavity in percussion hammers. As cast, those cavities are too shallow, at the wrong angle, in short, wrong. So I ground the tip off the bit, ground a taper to the tip, and then some relief to allow it to cut. I have re-cut literally hundreds of hammers with this same tool, without having to sharpen it. The photo shows an example.
The second is a mandrel I made to lap rifle barrels as small as .40 cal. It is made out of a section of bridge spike (mild steel). One end is threaded 8 x 32 for a cleaning rod, and the other, 10 x 32 with a nut and washer, for forcing the lead lap up the taper to increase it's diameter. The rod is inserted into the centre of the barrel's breech, with a rag plug to stop the cast in the bore. Several inches of the rod protrude from the barrel. The lead is cast over the rod, and it is marked for index with the sight. Then it is removed, attached to the swivel handled rod, the nut given a turn, the lap charged with oil and abrasive, and reinserted into the bore. After ten trips down the bore, the lap is pulled out, tightened, and recharged, and the process repeated. After 8 hours of this you have a slick bore with a slight taper, if you stop before exiting the muzzle.
