The answer based on the OP, said a gun that did not use a metallic cartridge, a metallic cartridge or lack there of does not define an antique handgun but rather the proven age of manufacture and the cartridge that it is chambered in. A flintlock pistol made in 1990 is not an antique but a revolver made in 1897 chambered for the 455 Webley, which is still chambered, is considered an antique.