I can agree to what you said, but you have to remember that all shotgun shells at the turn of the last century had fibre and cardboard wads separating the powder and shot. Long tapered bores going to long chokes would help the now loose shot stay tighter when hitting these areas and for a short distance after it left the barrel. With todays plastic wads I think most of this tighter constriction is built in.
I found it curious with the above mentioned barrel on how the shot seemed to carry it's pattern longer than I would have expected.
