The usual method is to use a carbide bit to break through the skin, then a standard bit to drill the main hole, and finally the carbide bit again to break through the other side's skin. I use a 3-flute carbide bit sold by Brownell's and it works well.
Many times the hole will then need to be annealed to allow tapping the threads and this can be somewhat tricky. If heated too much, to a red heat, with the heat source removed abruptly, the steel of the hole will then be quenched and re-hardened by the cooling action of the surrounding unheated steel. The solution is to heat the inside of the hole so that the bright steel turns blue or purple, no hotter, and then remove the heat source slowly. The steel in and around the hole will then be soft enough to tap the threads.
An alternative spot annealing method prior to drilling the hole was detailed by Maynard Buehler in the first edition of Brownell's Gunsmith Kinks. He suggested heating a separate cube of steel to a red heat and then placing it in contact with the receiver at the hole's location, and allowing it to cool slowly. This would theoretically anneal the spot of the hole without changing anything else or discoloring the steel. I've never tried this method but apparently it works.
Sounds as though you may need a different smith...
Regards, Joe
