Here is a soldering iron I've made today.
The tip is a chunk of copper I forged square and then to a tapered point. it was bored through in the back and then threaded to accept the threaded shank of a long nail which I had ground to a taper on one end to push into a handle while hot.

The handle is made from a piece of sassafras wood and the ferrule is a .308 Winchester cartridge. The cartridge was cut a little past the middle towards the necked down portion and was rammed open with a tapered drift and spread open further with the horn of a small bickern so it's a nice tapered ferrule.

I made some solder as well and that is what it is tinned with on the tip. Quite fun to use these with a gasoline blowtorch or a charcoal tinsmiths stove (which I will make later on)