Hardness of older 3 screw model Ruger Blackhawk frames

[Flatsguide]

I need to do a bit of engraving on one of these that I mentioned in the title. I have read they are hard steel and difficult to engrave. I wonder what a good alloy of the graver steel would be best to try. Any thoughts or suggestions much appreciated.
Thanks Richard

 

[Dani Girl]

Carbide graver blanks are the hardest we use. Are you chisel engraving or rotary engraving or ...? What is the afore mentioned... knife... gun? maybe pictures could help. Whare are you working on and what are you trying to achieve?