Duel(l)ing pistols are pistols of identical appearance, reliability and accuracy that were used in a classical duel. As a general rule, they are single-shot flintlock or percussion black powder pistols which fire a lead musket ball.
The use of pistols in duels became popular in Britain, France and the future United States during the mid-eighteenth century. Initially holster or travelling pistols were mainly used, but by the end of the century special-purpose dueling pistols were being made by craftsmen in England, France and other countries e.g. Germany, Austria and America.
The dueling pistols of this time were sold in pairs, usually in compartmentalised wooden cases along with a powder flask, rods for cleaning and loading, spare flints and a bullet mould.
Standard flintlock pistols have a noticeable delay between pulling the trigger and actually firing the bullet. To fix this and other disadvantages, purpose-built dueling pistols featured various improvements to make them more reliable and accurate e.g. heavier barrels, a spur on the trigger guard, saw handles, platinum-lined touch-holes and hair triggers etc. Special care was taken when moulding the bullets so as to ensure that there was no hollow part in them. The loading was also carefully undertaken. Given that duels were generally fought at short distances (between 20 and 40 feet was typical), accuracy was not a major problem.
Duelling pistols generally had quite large calibers: 0.45 of an inch was typical, and frequently had calibers of 0.52" or 0.65". Additionally, a bullet fired from a duelling pistol had a muzzle velocity of ~800 fps, which compares favourably with a more modern automatic pistol cartridge such as .45 ACP. These factors, coupled with the primitive state of emergency medicine meant that duelling pistols could inflict severe gunshot wounds and therefore fatalities were common.
Most duelling pistols had smooth bores, though some had "scratch rifling" i.e. a subtle form of rifling which was difficult to see with the naked eye. Pistols with rifled barrels spin-stabilise the shot when it is fired, resulting in much improved accuracy. As a result, duelling pistols with rifled barrels were considered unsporting by many.