Hi,
Swamped round, 1, 2 and 0 banded octagon to round, octagon to 16 flats to round, all of those are historically correct. It all depends on what you are building or buying. The most popular during the late 17th and 18th centuries was octagon to round with 1 band but that was likely because of the popularity and esteem for Spanish barrels all throughout Europe and Britain. That style is called "Spanish form". However, French sporting and trade guns were often different, and so were fowler barrels from other countries including Britain.
dave