Mike--As I read the proofmarks, your gun does not appear as old as you think it is. Unless you have something else (like maybe a serial number list?) telling you it's turn of the century, the proofmarks tell me it's no older than 1925. Guns with both chamber length and shot charge--unless they've undergone reproof, and I see no indication of that on your gun--were proofed under the rules in force from 1925-54.