Thanks Eagle --
Closer look and reference to my reloading manuals, more probably a 300 Winchester Mag -- or the like. That would suggest the slimline style. There are a number of 30-06 casings in the garage that my father sent me via his "policing the brass" from the American Legion Honor Guard activity. They shot blanks which were made from rejects with flawed primer pockets. They should make good pens though....
Reloaders anneal brass necks to avoid splitting during the sizing processes. Heat the brass to a dull read and dump it into water. Normally you do not want to soften the head of a shell, but it would make drilling easier.
In reading through past threads, I did not find any reference to any silver solder or high-force solder being used to bond the brass tubes to the shell casings. Will have to try that, as it would provide a more positive long term connection than most of the glues. I have a bag of slimline style parts to experiment with.
Please keep on showing pictures of pens and jigs. I enjoy the puzzles you provide for me to try to solve with the photos. I am not interested in coppying what you do, (as if I could), but always appreciate your sharing what did not work. I just go the same place more carefully.
Blessings!!!