http://www.nramuseum.org/gun-info-research/hard-to-identify-or-value-firearms.aspx
ANTIQUE FLINT & PERCUSSION GUNS - "BLACKPOWDER," "MUZZLE-LOADERS," etc.
Original handmade flintlock & percussion ("cap & ball") firearms. These are original antique muzzleloaders that are made by individual gunsmiths or small manufacturing concerns, usually prior to the era of mass production, but sometimes well into the mid-19th century. There are literally thousands of small individual makers, and often such guns are unsigned with no sure way to identify the maker. In these cases, an expert hands on inspection may result in a reasonable estimate of value based on such factors as probable maker, condition, quality of construction, style & extent of decoration. Some may have considerable value, in thousands of dollars. Others, such as well worn no name double barrel shotguns of average quality & low condition may be worth well under $200.
Some general considerations for antique flint & percussion arms by small makers:
- Generally, signed guns will bring more than unsigned. The gunsmith is generally considered to be the name (if any) that appears on the barrel. Often gunsmiths purchased pre-made locks from small manufacturers, especially during the percussion era, and the name appearing on the lock will often be the lock supplier rather than the gunsmith.
- In the U.S., American-made guns tend to be more desirable and more valuable than others, especially from the flintlock era. European - especially English, French, German, and Italian - guns can also have good value. Generally, but not always, Belgian-made guns will have a bit lower value ("ELG" proofmark indicates a Belgian made gun.
- The type of gun will impact value. Among American-made guns, generally flintlock will be worth more than percussion (guns that started as flintlock, were converted to percussion, and more recently converted back to flintlock will bring less than original flintlocks); full stock will be worth more than half stock; rifles tend to bring more than fowlers. There are many exceptions to all these generalizations.
- "Tourist" guns - These are often North African, Mid-Eastern, or Balkan in origin. Flint and other early pattern gun have been made in these regions for sale to tourists for centuries, and are still being made today. They are often artificially aged and sold as old guns. The majority that show up in the US tend to have little value beyond decorators, altho some of the older ones may have some value. They are often very ornately decorated with mother of pearl and wire inlays, although the workmanship will tend to be crude. Some will copy European designs, including copying makers' names. Others will have distinctive regional features.