The Hawks are really easy on the old guns. I don't know right off what the hardness spec is but they do seem to be softer than many others.
That article in DGJ that you're referring to, I believe, is the one written by Jeff Munnell. If I'm recalling correctly he included pictures of one of his early hammer double rifles that is quite a bit like yours. Jeff is a very experienced hand-loader and as you probably noticed, an entertaining writer. The .43 Mauser is all over the place when it comes to bore and groove diameters with most seemingly running on the higher end of the spectrum.
