RedofTx:
Not common, especially in 12g. A good one according to pictures. Cartridge is most probably 8x57IR (.318), offered by Sellier & Bellot or handloaded. Shotgun chambers are likely short 65 mm.
The drilling was proved November, 1936. Name on barrel is local seller/gunsmith.
Scope is Austrian postwar, Kahles variable 2-7x, a good one if a bit heavy due to steel tube.

Cheers,
Jani