..And... A Modern Reproduction Mfg of an Antique cartridge firearm (for example a Repro Henry Rifle) IF the reproduction is chambered for a cartridge no longer in production and not currently avail in commercial trade,,,,is also classed as an Antique Firearm (not a 'Firearm' under the GCA68).

( That 'Chambered for a cartridge ..and not available in commercial trade ' is an awfully gray area IMO. But what language isn't when it comes to many of these regs .)