49 CFR § 1544.203 - Acceptance and screening of checked baggage.
(a) Preventing or deterring the carriage of any explosive or incendiary. Each aircraft operator must use the procedures, facilities, and equipment described in its security program to prevent or deter the carriage of any unauthorized explosive or incendiary onboard aircraft in checked baggage.
(c) Screening of checked baggage. Except as provided in its security program, each aircraft operator must ensure that all checked baggage is inspected for explosives and incendiaries before loading it on its aircraft, in accordance with § 1544.207.
(1) Prevents the unauthorized carriage of any explosive or incendiary aboard the aircraft.
(e) Refusal to transport. Each aircraft operator must refuse to transport any individual's checked baggage or property if the individual does not consent to a search or inspection of that checked baggage or property in accordance with the system prescribed by this part.
(1) Any loaded firearm(s).
(2) Any unloaded firearm(s) unless -
(ii) The firearm is carried in a hard-sided container;
(iii) The container in which it is carried is locked, and only the individual checking the baggage retains the key or combination; and
(iv) The checked baggage containing the firearm is carried in an area that is inaccessible to passengers, and is not carried in the flightcrew compartment,.
(3) Any unauthorized explosive or incendiary.
(g) Ammunition. This section does not prohibit the carriage of ammunition in checked baggage or in the same container as a firearm. Title 49 CFR part 175 provides additional requirements governing carriage of ammunition on aircraft.