Rare American "Kentuky" rifle signed "J.M."

datable to ca. 1840: heavy barrel with hexagonal section, small caliber rifled bore, equipped with interlocking front sight and rear sight and windage adjustable with simple mechanical intervention for shooting accuracy;  battery with elegant swan neck dog, engraved on the folder  with initials "J.M."; trigger chain equipped with "stecher"; pleasantly flamed American walnut stock, complete with brass mounts including the classic "patchbox" on the right side of the blade; original wand with brass ball striker and iron rag hole; in excellent condition with beautiful old patina

L  136 cm

J.M., possibly identifiable as John Marshall, see "Database of USA Gunmakers