General info question about drilling and tapping hardened metal like receiver or barrel for scope mounting. First off, I have no intention of doing this, just interested in possibility. Do you "spot" anneal the target location, or just use special hardened machine tools? I've heard of packing an object in special heat absorbing/disipating comppund and using a torch. In the military, I have used a "carbon pile" to cut lock shakles. (24 VDC truck battery, jumper cables, and a carbon pole from a carbon-zinc D cell battery, sharpened to a point. Peck at the metal; it acts like a cutting torch to eat away the metal) If the sharpened tip is held on one spot, the metal will turn red and the circle will grow. Removing the carbon rod will draw a small arc unless you disconnect the battery first. There will be a small circular discoloratiom, where, I presume, the metal is now annealed, and more easily drilled and tapped. Can the "carbon pile" method be used to spot anneal a receiver?