Lucian,

The barrels are damascus. There were several different ways a damascus barrel could be "finished". The Germans seem to have preferred an acid etch. In addition to the example above, there is one with the etch finish here.
http://damascus-barrels.com/Finish_Restore.html

Is this the gun you are talking about? The "Nicht Fur Kugel" is "Not for Ball", essentially that means the gun is choked.
https://gunbroker.com/Auction/ViewItem.asp?Item=130216588

Pete

http://www.damascus-barrels.com/Movie.html