I'm in Yondering's camp on this. Polygonal rifling was the norm in the early period of gun making, notably by the Brits and others in Europe. They shot lead quite well back in the day. Keep in mind that "poly" means whatever the barrel maker wanted it to mean and the dimensions where his to craft. Also know that many shooters from that era used paper patch which inserts a very different metric in the game so far as leading/obturation/precision goes. 6 flats, paper patched pure lead? Hell ya!
Yup, that is a good point (the bit in bold). Some modern examples - HK uses (or did use anyway?) 6 flats in their 9mm hexagonal polygonal bores. Glock uses a series of flats and rounds (the flats are the "lands" in traditional rifling), and BHW uses Caudle rifling which has no flats but is shaped from 3 offset circles. All of them call their style "polygonal rifling".
