AndrewM,
I have a few but I am certainly no expert so please take what I say with a grain of salt.
Is it possible that the DP?M could actually be a DR?M with the second letter that looks like a P actually being a light strike R? The reason I ask is that this means Deutsches Reich Gebrauchs Muster loosely translated "German Empire Registered Design". Also I did not find any reference to a J. Vogel in any of my books on Drillings. My assumption is that yours was "made for the trade", in other words one of the gunmakers made the gun to be sold or marked by a sporting goods shop. Prior to the gun being shipped it as engraved with the shops name. This was a common practice during this period of time.
Good luck in your search. I also sent you a link (in a PM) to a site that might be of further assistance.
Respectfully,
WBLDon
