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Spot anneal the locations to be drilled by putting the tip of a red hot pointed copper rod on them a couple of times or you can carefully grind away the case hardening with a pointed Dremel stone.
An alternative method of spot annealing if you have a battery charger with a start/boost you can electro heat the spot by using a carbon point electrode. Put a point on the carbon and connect to plus clamp, put the charger ground clamp on the recoil lug, and just put the carbon on your mark and hold until the surface just starts to go past red at that spot. Do this in dim light. :thup:
"One can harvest a carbon rod from an old AA or AAA battery."
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An old gunsmith here used one of the old copper soldering irons like a plumber use to use to spot anneal receivers. He would clamp the receiver in his drill press vise, and then chuck the cut off soldering iron in his drill press, lower the heated soldering iron down onto the spot to be annealed. When the soldering iron cooled, the receiver was spot annealed in that spot. Repeat for the other holes.
