normally I don’t join a discussion where a potential seller is looking for a good auction description for free and doesn’t want to have anything else. But what was written here up to now makes me change my mind.
The gun is a Sauer model XIV and it was made around 1906/1907. The DRGM #130,243 (something similar to a patent, but not quiet the same) was registered on 14th March 1900 and is for the axle rib acting as a cocking indicator. This device was used by Sauer up to the end of the thirties, but the DRGM mentioning can be found (for legal reasons) only between 1900 and 1907 approximately.
Regarding proofs: Standard proofs used in Germany for shotguns between 1893 and January 1940.
DRGM: abbreviation used between 1891 and 1945.
Regarding 1912: nope, the date code marking did not become mandatory in 1912. The Suhl proof house started using this in September 1923, the Zella-Mehlis proof house did it earlier. But usage was not mandatory.
Chamber length: yes, sure, short 2 9/16” ( 65 mm).