Thanks to the generous donation of John S. Williams, the Princeton University Library holds a shotgun (not rifle) once owned by John James Audubon (1785-1851). A recent inquiry about the marking on the gun led Gabriel Swift to photograph and document various elements of the rifle, which stands at 157 x 13.5 x 5.5 cm.
In addition, there is an entry on the rifle in the 1959 Howard Rice exhibition catalogue, found full-text at: http://libweb5.princeton.edu/visual_materials/pulc/pulc_v_21_n_1and2.pdf. Item no. 146 “This is presumably the gun shown in the portrait by John Woodhouse Audubon (previous item). It is a muzzle-loading percussion-cap shotgun, made by Conway, of Manchester, England. An engraved inscription on the barrel reads: John James Audubon, Citizen of the United States. F.L.S.L. [Fellow of the Linnean Society of London].”
Rifle once owned by J.J. Audubon, no date. Gift of John S. Williams. Museum objects collection GA 2012.02563