Hi Andy,
Ezra is right about dueling pistols made during the late 18th century. A swamped octagon is very appropriate. Before about 1770-75 some dueling pistols had swamped octagon to round profiles but the fully evolved English dueling pistols used swamped octagons. Later in the 19th century, the barrels remained octagon but became heavier and sometimes had just a gentle taper. I've handled several dueling pistols from that later time period and I do not care for how they feel. I am a huge fan of those pistols made during 1775-1795 and in particular those by Robert Wogden. The finest handling pistols I ever set to hand were a Wogden (single survivor of a pair), and (at the risk of being accused of conceit) the Wogden inspired pair I built a few years ago. If I can pry them from my brother, I'll bring those pistols to Dixon's this year. One thing to consider, Andy, the light and handy balance of Wogdens and pistols like them have a wonderful feel but many target pistol shooters prefer heavier barrels. The later duelers probably make better target pistols for steady, deliberate, and slow aiming.
dave