Gotta love Google. Here is an e-library holding of Lewis's American Sportsman that discusses the various metals used. It also discusses fraud and sham artists in the gun business. Read pages 34 and 35 from this
link. The writing style is a treat to read as well. Of great interest to me (no prior knowledge) is the description of making "stub twist", the "stub" being
used and rusted horse/mule shoe nails left over after the animal is re-shod. Those are then cleaned to silver shininess and blended with steel in a forge oven. It could take 40 to 50 pounds of "stubs" to make one barrel. Interesting example of early re-cycling.
Cheers,
Jack