Here you go Rich
Gauge was marked starting with the 1855 Rules of Proof
Bore dimensions and marks post-1887 Rules of Proof



If a plug gauge of 0.710" diameter (but not one of 0.719") will enter the bore to a depth of 9" the barrels would have been marked 13.

BTW: Bore in inches was marked starting in 1954; in metric starting in 1984 to the 1889 Revisions.