Barrel bung hole reamer?
Rob
Yes.
It seems very large to be used by hand, but the handle obviously doesn’t attach to anything save a hand.
I was thinking a water well drill bit, but again, it can’t connect to anything.
Thanks for the link! I had one of these on my site 3-1/2 years ago, it’s a cooper’s splitter, used to split a white oak sapling for making wooden barrel hoops. The one that I posted can be seen here:
The only other reference that I have for it is on page 449 in the ‘Dictionary of American Hand Tools’, I recommend this book to anyone interested in tools.
Thanks, Emerson! The 3rd & 4th pics on the link match exactly.
Now I wonder just how it was used. Looks like it was struck after all.
I love the 'Dope!
And I feel honored that Emerson used one of his valuable, once-yearly posts to respond to me. 
Great that this has been solved. As a last resort I was going to suggest microwear analysis, which can be used to show what a stone or metal tool has been used for. I suspect it’s rather expensive however.
Just as a confirmation, we’re going to take this tool to Ralph, who runs the sawmill nearby. His dad (now deceased) was quite a cooper, I hear, and Ralph might recognize it.
For splitting staves cut from saplings/coppice, it might not be struck - it could be held against the end of the stick, then the opposite end of the stick struck against a hard surface - the momentum of the heavy iron tool thus driving itself into the wood.
Or it might be designed to be struck by a wooden mallet, rather than a steel hammer.
Cool! I was in the right ballpark.
Now what I really came in to post,
Your website should be banned. :mad:
Hardcore tool-porn like that is proven to lead to the purchase of tools that you really don’t have any use for . . . but are just to cool not to own. 
I have no need to carve my own spoons or bowls, yet somehow I own a spoon/bowl carving knife. 
CMC fnord!
Boy, are you easy.
this is probably it. I think back to the Woodwrights Shop TV show, he splits wood with various tools, and always uses a mallet instead of a hammer. Small pieces of dry wood split pretty easily.
(bolding mine)
I’m with you on that, crowmanyclouds. 
I don’t presently own ‘a spoon/bowl carving knife’, but after looking at that site, I sure as hell want one now!
Almost everything is, except for smithing and stone tools. But that handle would make a mess of the face of a wooden mallet if you struck it much. I suspect no striking is intended at all.
I’m not exactly buying the explanation. My extensive knowledge of coopery (that’s barrel making right? :)) would indicate that it isn’t used to make hoops, which would be either metal, or thin flexible strips of wood. Maybe it was useful for rough cutting or shaping staves though. But they would have been hand worked afterwards to get the angles and shape correct.
Staves, surely.
Would a tube with a large flat back have fit over the handle?
What would that do? (If it was used, I have no evidence.)
One could beat it with a mallet.
Here it is, a Cooper’s Hoop Cleaver. This one has a knob on the end clearly for hitting with a mallet. This was used for wood hoops, which were primarily used before 1800. So the tool in the OP could be very old and rare. I’m not sure how it helps cut wooden barrel hoops. The wooden hoops could vary from thin strips of flexible wood to inch thick material that had to be heated and bent on a form.