The Mauser Modell 1904 was a short- lived Mauser Export military rifle in 7x57. Both Colombia and China bought some. It was built on the same intermediate length action as the Turkish 1903, the Peruvian 1909 as well as most pre-WW2 commercial sporters in 7x57 aka .275 Rigby. As the receiver shows contemporary Oberndorf BU civilian proofmarks, it was originally delivered from the factory as a type C Army hunting rifle. Those humble sporters were often built on rejected or leftover military parts and keep military markings and serial numbers. As Rigby was the sole official Mauser importer in the early 1900s, other British gunmakers like Westley-Richards circumvented the monopoly. Often they bought complete military rifles through the international arms trade and tore them down for the actions. But there was a black market too for actions and parts smuggled out of the German factories, government arsenals as well as DWM. But more likely W-R here merely reworked a humble model C and sold it as an economy sporter.
Much later the barreled action was modified. The bolt handle was bent back, the action drilled for scope mounts, open rear sight removed and the Pacific receiver peep sight put on. Finally the barreled action was mounted in the orphaned stock of another Mauser actioned rifle. This stock was originally for a standard length action. Look at the right side photos: the ejection/ loading port cutout of the stock is too long for the shorter intermediate action. So the longer receiver ring overhangs this cutout to the rear by about 5 mm. These alterations were most likely done post-WW2 in the USA.