Well, with liquid duplication gone, I can now confirm that the metal cannon and liquid duplication are NOT the same bug. \
Behold, the Metal Printing Press, powered by dupes who refine steel, and a snapshot of a single printing.
The metal refinery uses liquid steel as the coolant. The window tile below the metal refinery connects a tiny blob of petro (above the tile) to the coolant pool below the refinery, keeping the refinery nice and chill. The liquid in the refinery itself