Justin, that was the crux of my initial question. But look at it this way: There were no fractional bore sizes prior to 1887. 12 was .729; 11 was .751. Thus, a gun that measured .740 from the factory would have been marked 12; couldn't have been marked anything else. And it would have been in proof. IF there had been a later reproof, then it would have been marked 12/1 if it measured from .740-.750.