(a) Law enforcement officers when using firearms authorized by the Chief of Police in their official duty.

(b) Persons in the Armed Forces of the United States engaged in official duty.

(c) Devices which are not designed or redesigned for use as a weapon. Any device, although originally designed as a firearm, which has been redesigned, or was designed initially for use as a signaling, pyrotechnic, line-throwing, safety, industrial or similar device, surplus ordinance sold, loaned or given by the Secretary of the Army pursuant to the provisions of §§ 4684(2), 4685 or 4686 of Title 10 of the United States Code is not covered by this Chapter.

(d) Those firearms that can not fire fixed ammunition but are loaded through the muzzle or cylinder with a combination of ball and black powder.

SOURCE: GC § 8900.1, added by P.L. 19-4:18.