That depends on where the transaction occurs. If a Maryland resident with a federal C&R license physically travels to another state and purchases a C&R-eligible handgun in that other state, OR if the C&R license holder purchases a C&R-eligible handgun from an out-of-state source and has it shipped directly to his licensed address in Maryland, then Maryland does not record or regulate that transaction. The Maryland State Police agree that such transactions are outside the jurisdiction of Maryland law, and they are legal under federal law as long as the C&R license holder follows all the C&R rules.
But, if a Maryland resident who is a C&R licensee comes across (for example) a 50-year-old (C&R-eligible) handgun at an estate sale IN MARYLAND, the usual Maryland-imposed transfer requirements do still apply -- the 77R application to transfer, the seven-day waiting period with background check, etc.. including involvement of either a state-licensed dealer or a "designated law enforcement agency" to sign the 77R paperwork. It is a C&R transaction in the eyes of the feds, but that does not "immunize" the transaction from state-imposed requirements.
I know that some Maryland resident C&R holders think that they can transfer C&R-eligible handguns back and forth with other Maryland residents, within Maryland, without observing any of the state-imposed transfer requirements, especially when they are trading with other C&R licensees. But it is clear that is not the position of the Maryland State Police. Nor have I been able to find anything in Maryland statutes or in the Code of Maryland Regulations (COMAR) that would justify any claim that C&R-eligible handguns, when transferred by C&R license holders entirely within Maryland, are subject to any different state-imposed transfer requirements than any other handguns (except the one-handgun-a-month law does not apply -- see below). If someone can produce any legal authority for such a claim, I would be most interested to see it.
(None of this discussion applies to an "antique" handgun, which includes any handgun manufactured before 1899, which by Maryland-law definition is not a "handgun" at all and therefore not subject to the Maryland transfer requirements.)
A federal C&R license holder is exempt from Maryland's one-handgun-a-month law, even if he does not have the state-issued "collector" status. This is explicitly provided in COMAR 29.03.01.04.
I am not a lawyer and this is not "legal advice."
ThatIsAFact
You are correct, I usually ignore any in state C&R transactions since MD controls those transactions. It is after all a logical view. The transaction isn't INTERSTATE if two MD residents want to trade guns, it is an INTRASTATE transfer, the Feds should have no control and only state law applies.
I was actually unaware that a C&R holder is exempt from the one in 30 day rule.