The federal age rule is not one threshold but two, and which applies depends on what is being sold. A licensee shall not sell or deliver any firearm or ammunition to an individual they know, or have reasonable cause to believe, is less than 18 years of age. Where the firearm or ammunition is other than a shotgun or rifle — or ammunition for a shotgun or rifle — the threshold rises to 21. So a rifle at 18, a handgun at 21, and the same split runs through the ammunition for each. The knowledge formulation from § 5.3 governs here too: it is what the seller knows or has reasonable cause to believe, not what a document asserts.

State law sits on top of that, and the regulation makes complying with it a federal obligation rather than a separate one. A licensee shall not sell or deliver any firearm to any person in any State where the purchase or possession by that person of that firearm would violate any State law or any published ordinance applicable at the place of sale, delivery, or other disposition — unless the licensee knows or has reasonable cause to believe it would not. This is the provision that gives the compilation from § 1.5 its practical work: the Director’s list of State laws and published ordinances exists precisely because a dealer is expected to know this and cannot be expected to research it unaided.

One more rule shapes who may be sold to at all. A licensee shall not sell or deliver a firearm to an unlicensed person they know or have reasonable cause to believe does not reside in the State where the licensee’s place of business is located — or, for a business entity, does not maintain a place of business there. Two carve-outs follow. The prohibition does not apply to the loan or rental of a firearm for temporary use for lawful sporting purposes under § 478.97. And it does not apply to a rifle or shotgun sold to a resident of another State where the requirements of § 478.96(c) are fully met — which include that the purchaser meets the licensee IN PERSON at the licensee’s premises to accomplish the transfer, sale and delivery, that the licensee complies with § 478.102, and that the purchaser furnishes the required information. The in-person condition is the one that decides most cases: this is not a mail-order allowance.