OK, it's called a drilling and mine was made by Krieghoff in Germany. My old drilling was made in Oct. of 1935 but Krieghoff is still makeing them today.
To use it, it has double triggers like most double shotguns. The front trigger is for the right shot bbl., and the back is for the left shot bbl... If you have an "rimfire insert bbl." in the shot bbl, then the front trigger still fires that bbl...
Now, on the tang there is what looks like a safety, but it's not the safery... (check out the pict..) The safety is on the side...
It's the bbl selctor. If you push it foreward, the front trigger will then fire the bottom (rifle) bbl, and at the same time the selector raises the rear sight so you have open sights to use, or you can snap on the scope on and use that.
It all works very fast and is easy to get use to....
As for price.... Depending on the cal's, age, quality, engraveing, and other things, a drilling will run from about 1K to over 15K and every where inbetween!
DM