THIS IS NOT LEGAL ADVICE. Big disclaimer.
I found this in the MD code:
ARTICLE 27 CRIMES AND PUNISHMENTS : REGULATED FIREARMS : § 442. Sale or transfer of regulated firearms.
(d) Sale by other than regulated firearms dealer.-
(1) A person who is not a regulated firearms dealer may not sell, rent, transfer, or purchase any regulated firearm until after 7 days shall have elapsed from the time an application to purchase or transfer shall have been executed by the prospective purchaser or transferee, in triplicate, and the original copy is forwarded by a regulated firearms dealer to the Secretary.
(2) As an alternative to completing a secondary sale of a regulated firearm through a regulated firearms dealer, the prospective seller or transferor and the prospective purchaser or transferee may complete the transaction through a designated law enforcement agency.
(3) A person who makes an application to purchase, rent, or transfer a regulated firearm by secondary sale shall pay a processing fee not to exceed $20 to the regulated firearms dealer.
(e) Disposition of copies of application.- The regulated firearms dealer or designated law enforcement agency shall promptly after receiving an application to purchase, rent, or transfer, completed in accordance with subsection (h) below, forward one copy of the same, by certified mail or by facsimile machine, to the Secretary. The copy forwarded to the Secretary shall contain the name, address, and signature of the prospective seller, lessor, or transferor. The prospective seller, lessor, or transferor shall retain one copy of the application for a period of not less than three years. The prospective purchaser, lessee, or transferee shall be entitled to the remaining copy of the application.
(f) Application fee.-
(1) A person who makes an application to purchase, rent, or transfer a regulated firearm shall pay to the regulated firearms dealer or designated law enforcement agency a $10 application fee with the application to purchase, rent, or transfer.
(snip)...
Section 441 states (in part)
r) Regulated firearm.- "Regulated firearm" means:
(1) Any handgun as defined in this section; or
(2) Any assault weapon as defined in this section.
This seems to leave out rifles/shotguns. I can't guarantee it's not covered somewhere else, though.