It is an Artillery stock.....probaly original,unmarked

To know if it is imperial made or before 1940, you just have to look the chamber. Chamber design is different as front part of the chamber, just near bullet is cylindrical, and after 1940, all the chamber are conical.
It is easy to see when you fire an old Luger, you have a typical mark around the fired case.

I have not been to the last few gunshows lately because of ill health. Will try to see him at the next show in his area. bigbill