About four or five years ago I took a class on color case hardening at Murray State College in Tishamingo, OK. John Hackley was our instructor. We were taught to select only receivers or parts that had a very low carbon content namely early 98 Mausers, early Winchester lever actions, Martini actions, shotgun actions, 22 rim fire actions, early Marlins, you get the idea. That way only the skin was hardened due to carbon introduced from the charcoal it was packed with. When quinched in water the core of the meatal remained soft and ductile while the outside skin turned out glass hard for a depth of anywhere from .005 to .020 thousandths deep.
If you use this same process on modern high carbon content steel such as ASI 4140 which I believe Ruger No. 1 is made from, the result will be glass hard and brittle steel all the way through. Now if you have access to a good sophisitcated knowledgeable heat treatment facility, they can then temper that same action back down to the desired hardness range, approximately Rockwell C scale of 45.
So in other words the color case hardening proceess for low carbon content steel can be carried out in a small shop providing you have good equipment, however when you start fooling with modern high carbon steels you should plan on using a good reputable heat treatment facility for follow up tempering and hardness testing.
I dont pretend to be an authority on the subject but have had some experience and instruction from a good teacher.
By the way you should see the color photos of some of our projects being quinched at 1425 degees f at night! I wish I had a way to post them.