FWIW: We checked the barrel dia. at several points along the length of the 45-70 BC and the 38-55 TM. The BC is a longer tube, but the taper breech to muzzle is the same. That is to say, the shorter TM at muzzle is the same dia. as the BC at that length.
I dont know if the shorter 'Handi' barrels are similar within their class (bull, sporter, etc).