Here are two different barrels from fowlers one flint American pre rev and the other 1850 English. The first measurement is the length from the breach to the point at which the profile of the barrel is measured.
American Pre-Revoulutionary
Barrel length 39.5" .664 Cal. full stock
breach= 1.30, 12"= .948, Wedding band at 15.5"= .912, 18"=.876, 24"= .822, 28"= .817, 32"= .807, 34"= .800, 36"= .803, 38"= .830, 39.5"= .882
English 1850's Hooked breach style with under rib
Barrel length = 32.5"
breach= 1.275, Wedding band at 8.75"=1.033, 12"=.943, 16"=.893, 20" =.866, 24" .862, 28"= .842, 32"=.850, 32.5= .883