Neil,
Your musket is a Liège (Belgium) made gun, a copy of a French regular model (1842, 1853 or 1857) with the typical back action lock. The North bought thousands of this type (3 band, but also 2 band, the latter as the so called Chasseur de Vincennes type), often referred or intermixed as French muskets but mostly of Belgian (Liège) manufactory (from Francotte, Ancion, Monseur, Malherbe etc.) but the Confederates only a few. There is only one existing hint that a small number of these guns reached Savannah on 16th Sept. 1861 on board of the British steamer "Melitta" (see Whisker, Yantz, "Firearms from Europe", 2nd edit., p. 111). As far as I know there was always a Southern relation to the Liège made guns from Tanner, perhaps these were the "Melitta"-guns. The Confederates limited their foreign purchase on British Enfields (and perhaps a few older British models like the Brunswick and Pattern 1842) and Austrian Lorenz rifle muskets. It would be of interest to know whether Your gun has an adjustable rear sight or only a French type blocksight on the breech.
Regards,
Marc