I think I can say with some assurance that it is not a Luger 'Artillery barrel". The sight base is wrong.
Here is one on GB that has a soldered-on sight base. It looks a lot like yours. Artillery Luger sight bases were machined from the parent metal, not added afterward. Receivers were also notched to clear the rear sight leaf. There was no gap between the sight base and the barrel flange.
http://www.gunbroker.com/Auction/Vie...Item=221163376