Here's where you go to look it up.
http://www.access.gpo.gov/nara/cfr/waisidx_02/27cfrv1_02.htmlLook for part 178 and click on it. Then scroll down 178.11 and click on that and scroll down to the definition of an antique fireram
Antique firearm. (a) Any firearm (including any firearm with a
matchlock, flintlock, percussion cap, or similar type of ignition
system) manufactured in or before 1898; and (b) any replica of any
firearm described in paragraph (a) of this definition if such replica
(1) is not designed or redesigned for using rimfire or conventional
centerfire fixed ammunition, or (2) uses rimfire or conventional
centerfire fixed ammunition which is no longer manufactured in the
United States and which is not readily available in the ordinary
channels of commercial tradeA cannon that is less the 1/2 in bore diameter falls here.
You also need to look here
http://www.access.gpo.gov/nara/cfr/waisidx_02/27cfr179_02.htmlThis time scroll down to 179.11 and click on it and look for the definition of antique firearm.
Antique firearm. Any firearm not designed or redesigned for using
rim fire or conventional center fire ignition with fixed ammunition and
manufactured in or before 1898 (including any matchlock, flintlock,
percussion cap, or similar type of ignition system or replica thereof,
whether actually manufactured before or after the year 1898) and also
any firearm using fixed ammunition manufactured in or before 1898, for
which ammunition is no longer manufactured in the United States and is
not readily available in the ordinary channels of commercial tradeCannons greater than 1/2 inch fall in here.
Basically Muzzle load it,use matchlock, flintlock, percussion cap, or similar type of ignition system and you are home free. No fixed ammo.