http://jamesdjulia.com/item/3706-386/

Paul Mauser was very persistent - if ultimately unsuccessful - in his long-tim goal to create a practical semiautomatic rifle using a full-power cartridge. In total he tried some 17 different designs, including one in 1901 which suffered a burst casing during test firing and cost him an eye.

This particular rifle came just shortly thereafter, and uses a quite strong and safe long recoil action coupled with a 2-lug rotating bolt. Long recoil designs are fairly unusual in firearms, and this one has an interesting feature of a bolt handle which disconnects the barrel recoil spring when used (rather like Mauser's Gewehr 41(M) rifle, in fact).

The design reportedly had persistent problems with extraction and ejecting, unfortunately, and Mauser would drop it for other designs. At some point after its testing was finished, this rifle was sporterized with a cut-down stock and express-style sights (it was originally made in full military configuration). While unfortunate, that does not change the fact that it is an extremely rare example of a Mauser experimental rifle.