This is a very good example of "garbage in - garbage out". This is the last time I rely on memory alone to present observations for analysis. After thinking about how shrimpy an 18 pdr. would look, I began to wonder. Looking at my trip notes today AND calling the Fort Niagara curator, I found that the over-all-length of this piece is 10 feet 6 inches, not eight feet. Also the bore dia. is 6.5", not 5.8". So, now we know why it looked so huge to Mike and I when we were there looking at it. The curator also mentioned the only portion of it's provenance that they have is the very last leg of it's journey to Ft. Niagara; it came from Letchworth State Park located E.N.E. of Ft. Niagara fairly recently. Looks like it is solidly in the 6.4", 32 pdr. category. According to my book on Naval Guns, the Cipher is from the reign of George III, 1760-1820. Thanks Gary. Thanks Double D for mentioning the Palmerston Forts Society site. Back before email we occasionally wrote them letters of inquiry. Thanks Dan for noticing the sledge-hammer modified trunnions. Thanks tombstone270 for making me look even harder in my Naval Artillery book and know the diff between bronze and iron gun Ciphers. The one you posted is in my book under Bronze Guns. The Ft. Niagara gun is iron. Thanks KABAR2 for noticing the flintlock mounting holes a significant observation. Thanks Sir for pointing out those tiny numbers that I can't quite make out. Finally, thank you Bob Smith for making me think. You are the catalyst in this equation which caused the proper compounds to react and produce the sought-after, elusive, correct answer.
Tracy and Mike