Ed,
A nice Ketland trade pistol. The lock markings denote a Ketland pistol probably from the 1790's. The barrel proofs are important to dating these as well. See
Joe Puleo's article in Man at Arms Magazine Vol 33, No.6, 2011 for a great deal of info on the Ketlands. The magazine can be purchased as a "Back Issue" from Mowbray Publishing.
Kent Johns