It really is a firing pin! This type iron used a chemical heating
element that was placed into the chamber and started "burning" with the
plunger that punctured the end of the cartridge to begin heating the
tip. You had one chance to get your soldering done while the cartridge
lasted and then you had to wait for it to cool down to change to a new
one. It would heat about 10 min. They were prone to overheating and
the cartridges were unstable. My company used them for years for field
work but finally junked them and used vehicle powered irons (converter
from 12v). I think the last one was junked about 1960.

Jim

Roger Shoaf wrote:
My boss shows up with two old soldering irons today, one is a small iron
probably used for stained glass work but the other was rather strange. The
business end of the iron was about an inch in diameter and hollow. When
this is unscrewed, the handle end has a (for lack of a better description)
firing pin. This is actuated by a spring loaded plunger in the handle.

Any one know about this tool?