A really nice 1st model Long Land Pattern with all the proper furniture and markings. The original lock is marked 'Grice 1757' . The 46"barrel has a" U.S" surcharged designating  American ownership. These 1st mdl. Brown Bess' are what were used by the British in the French & Indian War. They were also used in the early part of the American Revolution at Lexington & Concord and Bunker Hill(Breed's Hill)  which in all probabilty is where this musket was captured.  A U.S surcharged 1st mdl.Brown Bess is without a doubt the hardest musket to acquire for any Rev.War collector.  
P.S Rock Island Auction just sold a 1st mdl. Brown Bess-U.S for $25587 that wasn't anywhere as nice and untouched as this piece. Sold