Belgian Sea Service Flintlock Holster Pistol; .69 caliber; circa 1810-1840.
Could have been used in the War of 1812 or perhaps the Texas Revolution.
The only external marking on this pistol is a "Crown / O N" stamped into the lockplate, forward of - and partially obscured by - the hammer. Underside of barrel near the breech are the typical Belgian proof marks.