Hi Hugh,
I agree that longrifle engraving was pretty crude compared with European work and drawing on the metal using some sort of whiting is adequate. However, I have trouble drawing smooth simple curves freehand on metal. It is pretty easy to draw on relatively flat patchboxes, but curved shapes such as buttplates, trigger guards, and barrel tangs are harder. I always have to figure out some way to rest my elbow on something to keep my hand steady. For me, it is so much easier to comfortably draw a design on paper and then transfer it to the metal regardless of its simplicity. The only exceptions to that for me are line borders (such as thick and thin) and nick and dot borders. I draw or scribe my guides for those directly on the metal. I think it is worthwhile for folks to learn good transfer techniques even if they only want to engrave simple designs.
dave