https://mpdc.dc.gov/page/transporting-firearm-district-columbia

Transporting a Firearm You Already Own for Registration

When transporting your firearm in a vehicle, it must be unloaded, with neither the firearm nor any ammunition readily accessible or directly accessible from the passenger compartment of the transporting vehicle. If the vehicle does not have a compartment separate from the driver's compartment, the firearm or ammunition must be unloaded and contained in a locked container other than the glove compartment or console. If you are transporting your firearm in a manner other than in a vehicle, it must be unloaded, inside a locked container, and separate from any ammunition.

Whenever in possession of a firearm, a registrant shall have in his or her possession the registration certificate, or exact photocopy thereof, for such firearm, and exhibit the same upon the demand of a law enforcement officer. (DC Official Code §7-2502.08)

Do not bring your firearm or ammunition with you when you register your firearm. Possession of ammunition for an unregistered firearm is prohibited in the District of Columbia, and you may be subject to criminal charges. If registering a semi-automatic firearm, do bring the empty accompanying magazine. Please note that it is illegal to possess a magazine that holds more than ten rounds of ammunition in the District of Columbia.

Retrieving Your Firearm From a Dealer

Under DC law, a firearms dealer cannot release a firearm to a purchaser until 10 days after the initial date of purchase. (DC Official Code §22-4508) A gun dealer will not release your firearm until you return with your approved registration certificate.