The idea of dueling was essentially you didn't aim. It was supposed to be a quick, non-deliberate snap shot with little thought or intent of accuracy put in. Rifling was not acceptable in England, and generally America, but France allowed it. As did the areas that followed the French pattern, like Louisiana, but then again the sword was preferred over the pistol in those countries far into the percussion period.
That said, tricks like heavy barrels to improve pointability, secret or shallow rifling, saw handles, psuedo sights, etc., were all produced and probably used. Dueling with pistols may have been an acceptable practice, but it was never a legal one. Thus a slow deliberate aim with a rifled pistol would have left a man open to murder charges that a snap shot from a smoothbore may not have. My understanding is that powder charges were also juggled to enhance or reduce the lethality of the encounter depending on the nature of the insult being settled, these matters being decided by the seconds between themselves without the principles knowledge. As was said before, given the short distances (10 30" paces was not uncommon, or 25'), rifled or smoothbore may have made little difference in hitting a man sized target, but had a large impact on the subsequent legal ramifications.
As was said before, a dueling pistol is one made to duel with. My favorite example is a duel with deringers over a dinner table, using cork bullets in place of lead. Not your typical duelers, but authentic all the same.
Joel
