I just came across this record in our accession files:
Harper's Ferry and Whitney 54 caliber rifle, circa 1851. Heavy steel barrel; Muzzle loader; Fine barrel; Brass hands and mountings; Brass butt plate; Patch box or place cut in butt stock to hold cleaning rag or caps; Brass cover with spring; Percussion lock. Bannerman Purchase. Sent to Smithsonian Institution 09/06/1950.
It was bought in 1912 for $2.50.