Kat:
I am stumped on this one, but perhaps others can educate us both! My understanding is that a 6mm JGA Karabiner is a German-made "garden" bolt-action rifle from the turn of the twentieth century (much like a single-shot .22 rifle for shooting varmints or small game).

It certainly may have belonged to someone, who, in his youth, participated in the Rebellion, but unless I have overlooked some aspect of the history of JGA, this weapon doesn't have any association with the Civil War.

John A-G
Iola, Wisconsin