I thought to pipe up, and state it doesn't look like the smaller "brass"
swivel cannons. One was once on exhibit in "New York Unearthed" at 17 State
Street in Lower Manhattan across from Battery Park run by the South Street
Seaport Museum. Not does it look like the "molded" one on the tribute to
John Peter Zenger on Governors Island, (*John Peter Zenger* was born in 1697
in Germany, and migrated to New York as a child in 1710 and lived there
before owning the second printing press in New York and tried for libel for
allowing an opinion contrary to the "official" press to be printed. The NPS
commemorates the "freedom of the press" that resulted at the St. Paul's
church "green" election site just over the the NYC (Bronx/Westchester). That
is across the bay there from where Herman Melville once lived, when he
worked for US Customs. They, however were in a sling like mount, or
represented  a curved mount I recall.

I worked in Skagway, Alaska for the NPS the summer of Mt. St. Helens, 1980,
and more recently I read that at one point in the 19th century a US gunboat
fired a Gatling gun over the Tlingit. Perhaps some gun like this was seen as
a threat, that they had and some one had the wrong info. The trunions don't
look right, bit I know nothing about guns per se. Looks like a heavier mount
wa srequired than a "rail gun".

George Myers