To make it I drilled out the back of a 50 cal. shell. I cut the primer side of a 308 shell off with a pipe cutter. Next I dropped the 308 shell into the 50 cal. shell. I reduced the mouth of the 50 cal. shell until the 308 shell fit snug. Finally I soldered it together and glued the mechanical pieces in place.
The fourth picture shows it compared to a .45 cal shell which is the same diameter of my original bullet pen.