Molly.
This appears to have originally been an Austrian M1849 'Kammerbusch' rifle for jaeger troops, or else the carbine version, depending on it's length. These are also commonly called 'Garabaldi' rifles. It would have started out with an Augustine tube lock but was converted to percussion in the late 1850's.Most of these conversions were carried out at Liege in Belgium. It only stayed in service for a few years and was superceeded by the much smaller caliber M1854 'Lorenz' rifle....A lot of these rifles, about 10,000, I think, ended up in the US where they were imported in the early part of of the ACW to fill the demand for any kind of military firearm. There's plenty of information on these rifles on the internet.....I have an extensive article on these rifles in one of the ACW magazines from a few years back which I can root out if anybody is interested. .........I know this because I acquired one at an auction where nobody much was bothered......I also got a bayonet for it afterwards......Collectors of ACW arms know these guns pretty well.
Niall