Serial is not military and proof isn't either. It once was a Suhler Claw Mount scoped Mauser action and has had the bases stripped. Not the military type, so a former commercial rifle, maybe once converted to a hunting rifle with scope bases made on basis of a military receiver, then someone tried to make it more valueable with stamps he found.
Only possible explanation for the serial number font could be Mauser commercial sporter, they also produced in this serial range. But that would require additional markings and I'm not sure on the font, plus this of course would not have the military acceptance (which once again is fake).