I don't know where you get your information from, but Washington DC is not a state, and furthermore.....
Washington, D.C., has enacted a number of strict gun-restriction laws. The Firearms Control Regulations Act of 1975 prohibited residents from owning handguns, excluding those registered prior to February 5, 1977; however, this law was subsequently overturned in March 2007 by the United States Court of Appeals for the District of Columbia Circuit in Parker v. District of Columbia. The ruling was upheld in June 2008 by the Supreme Court of the United States in District of Columbia v. Heller. Both courts held that the city's handgun ban violated individuals' Second Amendment right to gun ownership. However, the ruling does not prohibit all forms of gun control; laws requiring firearm registration remain in place, as does the city's assault weapon ban. Additionally, city laws still prohibit carrying guns, both openly and concealed.
DC residents were not prohibited from owning certain rifle and shot guns (black powder and smokeless) even under the old city rules.
AFAIK, Massachusetts has no ban on Uberti black powder firearms (ask several members here that live there). These MA regulations only concern dealer sales.