.719-.728 is actually UNDERSIZE of standard 12 bore. Since you know what the gun was proofed at, by measuring it, today, you can decipher what amount of tampering with the bore has gone on over the years. That information is far more relevant than what year it was built.

The gun is a 13 gauge. There was a time when they were common, but, the wads were typically horsehair at that time.

Best,
Ted