This is a very interesting and quite rare musket. There are only a few known of which four are in musums. One's in the Smithsonian, one's in the Springfield Armory museum and two are in the Maine State museum (Maine was part of Massachusetts in the Rev.War) . The Smithsonian believes that these early East India Co. Brown Bess muskets exhibiting to MS were American privateer captured muskets given to Massachusetts. The known muskets are of different British makers with the same date of 1779. This does imply that they all came from the capture of one ship on it's way to India. The reason they went to Massachusetts is because of the long standing animosity that existed between it and the East India Co. which went back to the Boston Tea Party (it was East India Co. tea that was dumped in the harbor ). The musket is in really nice condition. I would rate it as fine +. The lock is signed Wilson under the pan and East India Co 1779 behind the cock. The barrel has his R.W. (Richard Wilson) under a asterisk between two British proofs with the East India Co. heart shaped merchants mark and Wilson 1779 to MS. The MS is also stamped on the stock flat by the the top sideplate screw. Interestingly, all known examples of these muskets have surfaced in either Massachusetts or Maine.
As rare as the musket is the matching Bayonet is even rather. Actually it's the only one I know off.