This is one unique breech loading conversion of a 1864 U.S. Springfield rifle.
The origin is unknown, it has 1864 dates on the barrel and lock plate but no markings on the breechblock.
The rifle underwent a post-Civil War conversion to a .58 caliber rimfire via an unfamiliar mechanism that bears resemblances to the Needham conversion (side-mount configuration, unlocked breech secured by falling hammer).
Unfortunately it is another one of those firearms whose provenance has been lost in time.
Could this have been a Bridesburg Needham prototype?
Bridesburg Needham Conversion
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