SSShooter,
The octagon you see is straight. Doing a straight octagon section on a pre-tapered barrel is where all the work is at. Each setup has to account for taper in two planes. The barrel is shimmed off both surfaces that touch the vice. Once a flat is correctly established, the opposing side is only shimmed in one plane. After a flat and perpendicular flat are established, no shimming is required on opposite flats. The remaining four "angled flats" start the routine all over again. To establish the first 45deg flat, I clamped a vee block to the barrel and trammed its bottom surface....that facing the chuck. None of the final four flats referenced the first four by vice contact. I shimmed off the small wedge of remaining original cylindrical taper on the round barrel between flats. Whew....that was too much. 

Never mind the barrel...... I want that lathe!


JMH

SBoomer,
Nice job on the barrel, thanks for the reality check.  It's been many years since I've had to use machines in this manner I've bought mills of different types, super spacers, dividing heads, excess tooling, etc. even CNC's just to prevent ever having to perform operations and setups like this... again.   I do know the process and I admire your ambition.  Thanks for posting.   
Here's a wedding band I did early winter just to see if I could come close to the picture in John Campbells book.  Done a few more since, similar and different, they make a barrel original.  Haven't tried the inlay style yet but it's on the list.
Greg

SBoomer,
I spent quite a bit of time experimenting, thinking along the lines of what you mentioned, knurl then file, even made a concave knurl.  What I found out that worked slick and easy was a single knurl holder and very high quality roll.  The roll has to have crisp edges, nothing fancy on the holder - a piece of 1/2" square stock, drill and ream a through hole the size of the hole in the roll - a short hardened dowel for the axle and you're in business.   
Use the knurling formula to determine exact initial diameter to begin with (the knurl pitch, (ex. .040) divided by pi, and the result of that dividing evenly into the diameter. You can pick a size real close to the diameter desired - generally smaller as the kurling increases diameter slightly)  If this sounds confusing PM me and I'll email a more detailed step by step with examples.
Start the knurling process on the top of the prepped band, I took it close to depth in a straight on position, then I backed the tool out, re-positioned the roll at a slight angle and if you enter the form gently the roll picks up the lead, repeat this process until desired results are obtained.  I donned my magnifying visor and dressed the knurl with a very small file for the finish touches, under a scope at 40x it's a little coarse but with most eyeballs it looks good.  I've done a couple this way and moved on... the silver inlay is next... maybe gold? 
Greg