HiBC,
Mauser receivers were originally forged, although some where later cast by companies like Santa Barbara of Spain, which provided Mauser actions to companies like Golden State Arms and Parker Hale.
Odds are the crack happened during the forging process because the billet of steel had some slag, and because the crack is in a non-critical area it just passed the proofing process just fine.
Jimro
Mauser receivers were originally forged, although some where later cast by companies like Santa Barbara of Spain, which provided Mauser actions to companies like Golden State Arms and Parker Hale.
Odds are the crack happened during the forging process because the billet of steel had some slag, and because the crack is in a non-critical area it just passed the proofing process just fine.
Jimro