I see ur name is NYCguy so may I be so bold as to assume you live in new york? Take it to an antique dealer there.
Sounds cool tho. Good find whatever it is. Is it functional or all rusted up? Gun shop guys may know but I would ask one that sells older cowboy and decorative guns. Not to profile people too much but a young shop owner or clerk selling 2008-2010 sigsaurs and glocks mey not know, and initially I wouldn't take it with you. I would carry pics. On the off chance its real valuable. That's just me tho.
Maybe it'll be like those 2 guns in "Lock stock and two smoking barrels" if you haven't seen that its a guy ritchie movie that revolves around thes 2 pricelss rifles.
Guns don't kill people... but GOD they take a LOT of the hard work out of it!