[ScottRiqui]

I looked it up when I first saw his post, and it appears he's correct - the rule comes from the Maryland State Fire Marshall regulations. Anything over five pounds of smokeless powder requires a license. It also appears that you can't store powder in "multifamily dwellings, apartments, dormitories, hotels, schools, other public buildings, or buildings or structures open for public use."

§ 11-105. License required; exceptions.






(a) In general.- Except as otherwise provided in this subtitle, a person shall obtain a license issued under this subtitle before the person engages in business as a manufacturer or dealer, possesses explosives other than explosives for use in firearms, or possesses or stores explosives for use in firearms in the State.




(b) License to engage in business as dealer required.-




(1) A person shall obtain a license to engage in business as a dealer under this subtitle before the person engages in the business of loading or reloading small arms ammunition in the State.




(2) The owner or operator of a mine, quarry, or other operation or business that uses explosives, or a contractor who performs work that uses explosives, shall obtain a license to engage in business as a dealer under this subtitle.




(c) Exceptions - Armed forces and others handling explosives.- This section does not apply to the armed forces of the United States, the National Guard, the State Guard, or officers or employees of the United States, the State, or a local subdivision of the State who are authorized to handle explosives in the performance of their duties.




(d) Same - Possession of explosives for use in firearms.-




(1) Subject to paragraph (2) of this subsection, a person need not obtain a license to possess or store up to 5 pounds of smokeless powder for the loading or reloading of small arms ammunition, and up to 5 pounds of black powder for the loading or reloading of small arms ammunition or for use in the loading of antique arms or replicas of antique arms, if the smokeless powder and black powder are stored in their original shipping containers and are possessed only for personal use in firearms.




(2) A person may not possess or store explosives for use in firearms in any quantity in multifamily dwellings, apartments, dormitories, hotels, schools, other public buildings, or buildings or structures open for public use.




(3) Notwithstanding paragraph (2) of this subsection, the State Fire Marshal may issue a permit to allow temporary possession of explosives for use in firearms in a building or structure open for public use.