Transvaal,
The BRNO guns are made from what the Czechs called Poldi Elektro Steel which I assume was made in an electric reduction furnace. It is of very high quality, strong, and in my experience is fairly resistant to corrosion though certainly not stainless. The guns that I have worked with were not surface-hardened and I would think could be cut with a regular high speed steel graver. About 10 years ago I built myself a double rifle in calibre .450 #2 Nitro Express on a BRNO ZP-49 action. That gun has AT LEAST 1000 full loads through it and is still going strong and shoots wonderfully for a double. The Sable that I referred to above was taken at 208 yards, which is a good range for any double. I believe that that speaks well for the quality of these BRNO guns.