Thank you, shooter2. Your post made me look at the journal of field notes that we made while hunting cannons in New England and New York State this past summer. You are correct; it is a coehorn and the bore size is 4.5", not 2.5", (can't read my own writing!). Finally found our long-lost copy of Round Shot and Rammers. There on pages 40 thru 43 are some line drawings and artwork depicting the British version of the coehorn. Doesn't look too heavy, either, (only two lifting handles). Love that cipher for George III, very artistic. Maybe Douglas or Tim or Lance will cast one of these for us someday; they're building a foundry, don't you know.
Regards,
Tracy and Mike