Maryland Code, Criminal Law § 4-502

(1) a member of the armed forces of the United States or of the National Guard or law enforcement personnel of the United States, the State, or a political subdivision of the State while acting within the scope of official duties;

(2) an officer or employee of the United States, the State, or a political subdivision of the State who is authorized to handle a destructive device within the scope of official duties and who is acting within the scope of those duties;

(3) a person authorized by law to possess explosive material, incendiary material, or toxic material who is acting within the scope of authority if the possession of the material is specifically regulated or licensed by law; or

(4) a person who possesses smokeless or black gunpowder under Title 11, Subtitle 1 of the Public Safety Article and uses the gunpowder for loading or reloading small arms ammunition, antique firearms, or replicas of antique firearms.