Md
Bills work is really good. The term in use for gun engraing is basically
Hand engraved or simply engraved.
Engraved which covers all other types of metal engraving. This would be , everything from machine rolled , where there is a design placed upon a metal roller and the steel is rolled through the machine to accept the engraving , to chemical where the picture is etched into the metal.
There are even registered patterns for specalized engraved molds.
If you want to do a simple engraving the process is basically the same as with wood. Using engravers wax cover the outer surface of the steel, then use talc to give you a page if you will. Then draw your pattern in the talc.
After you have your pattern then use a scratch awl to mark the lines of your pattern.
From here it is a matter of using the skews and chisels to make the design. Or you can use an engraving bit .
Very similar to wood carving , just different media.
Here is a good site for seeing some of the work done.
http://www.engravingarts.com/engraver.html
Ash