Michael - Rifles with such markings exist. They were sold by Hans Tauscher of New York, an agent for DWM and Mauser Oberndorf before 1918. My sporting rifle is serial #100, in 8x57 caliber. I have corresponded a couple years ago with another collector with a similar rifle having a lower serial number. I also have somewhere a reprint of the 1912 catalog with line drawings of all sporting rifles in their line. This rifle does not appear to have been a worked over military action, but the raw materials could have been made about the time as the Brazilian 1908's. I believe the rifle was regulated to shoot the spitzer bullet adopted by the German military about 1905, weighing 154 grains. The 196 gr boat tail bullet was adopted after Hans Tauscher was out of business.
http://www.landofborchardt.com/tauscher-article.html