DC Code
DC LAw (DC CODE) is actually pretty interesting reading they have much different legal Definitions than Federal Law and "most" states, I have attached part of the legal definitions describing firearms under DC Code, I would urge each of you to look up the code and read it.
DC ST § 22-4501
Formerly cited as DC ST 1981 § 22-3201
District of Columbia Official Code 2001 Edition Currentness
Division IV. Criminal Law and Procedure and Prisoners.
Title 22. Criminal Offenses and Penalties. (Refs & Annos)
Subtitle VI. Regulation and Possession of Weapons.
Chapter 45. Weapons and Possession of Weapons. (Refs & Annos)
§ 22-4501. Definitions.
a) "Pistol," as used in this chapter, means any firearm with a barrel less than 12 inches in length.
(b) "Sawed-off shotgun," as used in this chapter, means any shotgun with a barrel less than 20 inches in length.
(c) "Machine gun," as used in this chapter, means any firearm which shoots automatically or semiautomatically more than 12 shots without reloading.
(d) "Person," as used in this chapter, includes individual, firm, association, or corporation.
(e) "Sell" and "purchase" and the various derivatives of such words, as used in this chapter, shall be construed to include letting on hire, giving, lending, borrowing, and otherwise transferring.
(f) "Crime of violence" as used in this chapter have the same meaning as provided in § 23-1331(4).
(g) "Dangerous crime," as used in this chapter, means distribution of or possession with intent to distribute a controlled substance. For the purposes of this definition, the term "controlled substance" means any substance defined as such in the District of Columbia Official Code or any Act of Congress.
That just a small part of the weapons section.