This is a very timely thread as I too have a Mauser that's difficult to identify.
Its a 98 with a thumb cut and has had all markings polished off including serial numbers.
The right side of the receiver is marked F 3 and on the receiver flat underneath is the letter K.
Any ideas / suggestions ?
Pic's would help
MiG25 nailed it. Spanish Air Force M44 that has been heavily modified. Nicely filled and polished thumb cutout. Some one did a lot of work to it.




























