Paul Mauser spent nearly 20 years attempting to perfect a self-loading rifle for military service. He came closest with this, his 1913 patent model, which was used by German balloon and aircraft fliers as the Model 1915 and Model 1916 respectively - but these rifles were also sold on the commercial market to affluent sportsmen and gun enthusiasts. This is an example of a sporting pattern 1913 rifle, with a sporting stock and full-length handguards, and a mounting rail on the receiver for a Zeiss prismatic optic. It has a 9mm bore, probably (but don't quote me) in 9x57mm. The mechanism, however, is identical to the military rifles.