Top gun appears to be a back action African Trade gun, circa late 1870 to 1900. Here's a link to the page I was looking at
http://www.ambroseantiques.com/flongarms.htm Scroll down, there are a couple of different ones listed. Here's a quote from the text...
EXTREMELY UNUSUAL & POSSIBLY UNIQUE AMERICAN CONVERTED BACK ACTION AFRICAN TRADE GUN, ca. 1870: Most probably a proto-type African Trade Gun, made by D. Kirkwood of Boston, (see G. Gardner). Made from a standard Belgian Import, Civil War Percussion musket, with its back action percussion mechanism having been converted to Flintlock. The band-secured, 42", rifled, .69 caliber barrel with bottom mounted bayonet lug, standard Liege proofs and "D. Kirkwood, Boston." stamped, in very small cursive characters, on the bottom left edge of the breech. Choice walnut fullstock with inspectors marks throughout. In overall excellent condition. The iron surfaces a smooth dark patina with no pitting. The stock retains all of its finish and has virtually no handling marks. All the markings are clear. Original iron ramrod. A very unusual rifled musket which was probably produced as a proto-type for a possible late 19th century African Trade venture. More research needs to be done on Kirkwood of Boston