Show me the law that said people in those days could not own a cannon...or a gatling gun. I don’t recall ever seeing such a thing.
When I was growing up in the 1930s, the family had a Bannerman Catalogue that had Civil War canons for sale for a few hundred dollars and a lot of other military surplus items. Someone in the family had bought a trapdoor Springfield with a ramrod bayonet that my brother and I found in the attic. I have a photo of my maternal grandfather with a carbine version.