As has been said, a fowler made from a musket barrel. These are commonplace and not particularly valuable, in New England. Mike is probably spot on regarding the barrel. It was most likely sold at one of the many auctions of condemned and obsolete parts. That was a common source of all sorts of parts, many of which were made up into muskets for militia members since they had to provide their own. The barrel could have been made by any federal contractor...the view and proof was done by traveling inspectors.
Another possibility (because the gun is so late I doubt this is the case) is that the barrel was simply taken from already inspected and proved stores, and sold. This happened quite a lot because the government was extremely slow paying the contractors. After the barrels were proved, the contractor received a receipt which he was supposed to turn in for his payment. Often he had to wait many months, sometimes years and the only way to stay in business was to sell some of the product. There were a lot of complaints about this on the part of the Federal officials but nothing ever happened because, at heart, they knew the problem was their own fault. In the end, nearly every Federal musket contractor went bankrupt, the major exceptions being Whitney, Pomeroy and Waters. All of them worked hard to find other customers and products because working for the Federal government was a dead end.
