The interesting aspect of your description is the part octagon barrel up to the first band. I have seen a few enfield rifles and muskets with heavier breeches than standard that extend out a couple of inches but never one up to the first band. If this is the case, you might also consider that this could be a different make of gun with an Enfield lockplate...or an Enfield with another type of barrel. I would love to see photos if you have them.

Brent Wilburn