It is unlawful to possess ammunition in the District of Columbia unless: (1) you are a licensed firearms dealer; (2) you are an officer, agent, or employee of the District of Columbia or federal government, on duty and acting within the scope of your duties; or (3) you hold a valid firearm registration for a firearm (except that no person shall possess restricted pistol bullets, as defined in DC Code § 7-2501.01(13A)).
Additionally, no person shall knowingly possess, sell, or transfer any “large capacity ammunition feeding device,” which means a magazine, belt, drum, feed strip, or similar device with a capacity of more than 10 rounds of ammunition.
Reference: DC Code § 7-2506.01