Ahh yes, the solid shot on the wooden base...it came from a land far, far away-
I see your point on the construction and in the end simply need to continue doing research on this puppy. It is not absolutely proven to be a barshot, nor is it absolutely proven not to be a dumbell (I must say, though, that it probably is one or the other versus a third option of counterweight, machine part, etc).
The best proof I had that it was mid-19th was the last site I listed which, unfortunately, is no longer accessible. That gent sold a number of cannons from all age and nationalities and had barshot EXACTLY like mine listed as 19th c. His site wasn't above some controversy, though, being a seller after all (some of his lanaka appeared more modern and poorly cast to be original), sooooo....hopefully, I'll run across a Civil War artillery expert someday who will finally end the speculation.