Dave, next I am going to make a test run in a piece of barrel blank. Since this stamp is circular, I can cut it with an endmill or a boring head. Cheating? If Herr Heinz Immel had one, he would have used it!
Seriously, if the stamp were odd shaped, like a shield, for example, I'd cut a pocket first by milling, then finishing up with chisels and gravers. Once the pocket is prepared, THEN the gold is stamped in place. The deep pockets I have seen in the Steinschloss book look cut to me, rather than pressed or pounded. As Dave mentioned above, the bore could be badly distorted with enough pressure.
Ironwolf, I used a surface grinder to flatten the face of the stamp. Initially, I was thinking of making a background of parallel lines, but then I'd have to line the stamp up PERFECTLY with the barrel, or it would look strange.