Since we are just making guesses I'll make a few. Nice gun no matter what the origin.

Innovative & cost effective trigger adjustment by the way. The receiver and bolt
look pre WW1 and would be surprised if it was not an Oberndorf. The barrel profile especially
the key slot would also suggest pre WW1.

The stock and bottom metal suggest post WW1, looks almost HVA in style.

So someone took a barreled receiver and put it into a "new" stock for whatever reason, most
likely the original stock was "discarded".

Pics. of the underside marks etc. should prove interesting.

Like I said suppositions only FWTW. --- John303.