Something else that might help pin it down, the length. I have a brown Bess bayonet which according to Neumann's book is pretty much standard fare. The length is a 16 and 1/2 inch blade and is 19 and1/2 inches overall. By the way it was at one point tinned to retard rust and can be dated from the proof mark (small crown over 9) to sometime after 1771 so it was probably for the second model Bess. It was issued to the 7th regiment (fought at Monmouth Court House in 1778), Company A. The bayonet which came with my Model 1816 (pretty much a clone of the 1771 Charleville) is 17 and 1/2 inches overall with a shorter 13 and 1/2 inch blade. It is marked with a fairly large and deeply impressed US and in smaller letters JU. From your picture I am inclined to the smaller length and still think American contract bayonet of the above dates. Please, if you find out more write back and tell us what you found. As you might suspect, attributing original arms, documents, coins is a most pleasurable part of the hobby.