These days I think it is easier to perform engraving using a CNC mill or CNC laser.
One particular program makes it easy to do even "one off" designs. Artcam
www.artcam.com, check out the site they have some neat demos. It is used by jewelers to create reliefs in rings, bracelets etc.. I have not seen it applied to gun recievers, although it would not suprize me that someone is using it this way.
This seems like a more profitable approach. I can't imaging hand engraving a font when one can select any true-type font and have the machine engrave it using a diamond tipped tool.
Purist my frown, but I think so long as the designs are unique and what the customer desires than I see nothing wrong with using CNC.
After all it's not the tools, but how good the artist is at using them.