Try the exact spot where it's to be drilled and see if it is indeed case hardened there. I've had a couple of Krags and '03s that were able to be drilled and tapped with nothing more than regular HS drills and taps. The negligable surface hardening in the area was easily punched through with the drill and it's soft underneath as it's supposed to be.
If it is a deep hard case, the exact spots can be marked and a very small cone point grinder stone (Dremel type) that can be drill press mounted can be used to first grind thru the case. Make the spot just slightly larger than the needed hole and tapped thread to be cut so you're working in the soft metal only.
The old method of drawing off the hardness with either a very small torch tip like an '0' or the soldering gun trick works, but can either leave a ring of discolored metal in the first instance if it gets away from you and can be very slow in the second instance in my experience.
Another way, if you have them, is to just break through the case with a slightly larger diameter carbide drill.
