I got this from my step-dad. He used it many years ago and he described how it worked.
It is not a cannon. What is it?
It has an unusual muzzle:
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It has a powder chamber (about 3" deep too).
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And it has a most unusual touch-hole - about 1/4" in diameter for most of the depth and less than 1/8" in diameter where it leads into the powder chamber.
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I've only seen one or two others in my life and run across one or two old-timers that knew it's purpose.
It is a tool.