If I recall there are no other markings on the barrels. Unfortunately I don't have access to the gun to snap another photo anytime soon.

Thank you for all the info so far. You've added a lot I did not know. Any thoughts on the lack of serial number on the drilling?
You mentioned Blitz, I'm not familiar with that term, can you explain? Are the bright barrels unusual?

You mention Merkel A&D, what does A&D stand for? You also said the DR might be some sort of Kerner-Anson, does that mean it may not be a Merkel?

I apologize for so many question, I'm quite intrigued by these guns.