Interlocking copper core sections.
Previously made to fit inner core copper tubes.
I cut a 33mm section off the outer core tube and filed ends flat, then cut a 16mm section.
Cut a 25mm section off the inner core tube and marked out slot positions on the ends of both sections.
Cut slots into both ends.
Using the file then flat stones I smoothed off the end sections square...
To make two neatly interlocking inner core tube sections.
The idea being, with the rotary tail switch, the sections will not move when holding the light/ rotating the switch. 
Most of the inner & outer copper core pieces, exploded view.
Showing interlocking sections and head rubber o-ring placement. 
Inner body cores roughly put together. The tail end still requires to be shortened to fit the cell & rotary switch.