It is either a Franz Jäger or Simson sourced sporting weapon as that is their patented lockup. Would fancy an image of the top rib extension and of the water-table. The original chambering looks to be 8x58 - maybe Sauer and possibly converted? Do a chamber cast. What is the jagged encircled stamp near the forend hanger? Made between 1912 & 1912. Is the name Meffert in Hamburg or does the name begin with a V?

Kind Regards,

Raimey
rse