Gunwork is a favorite of mine as well...I regard real gunsmiths as ultimate Toolmakers. Got my start, 1960's reading about J.M. Browning in sixth grade.
Anyway, on replaceable punches; I built them like the primer punch of reloading dies but far more depth of engagement in the body. Bottomed out in the head for positive impact. 01 Drill rod for softer punches, drill blanks for tough ones. Bodies of drill rod too, but W2, was economical, machined and knurled beautifully.