Never having been able to get a nice, even, aligned stamp on a barrel I decided to make a fixture to hold the stamp while striking with a hammer.  Since virtually all the stamping done is on the breech end of the barrel the fixture was made as a feature o
In use the bushing is slid over the barrel with the slot positioned over the area to be stamped.  This assembly is then clamped in the bench vise equipped with padded jaws while being supported underneath by a block of wood.  The type slugs are installed 
FWIW