Gun Ring - Ca. - was originally designed for ladies. (I read they got very hot after firing. and given the way people move their hands around, I would think wearing a loaded weapon on your finger would not be a very good idea.) MY KINDA JEWELRY
This is an antique, German combination gun (according to the OP) that appears to have several gauges of ammo, like a rifle, shotgun, and pistol bullets. The flourish designs on the gun are beautiful as well.