From what I read (a few months back, so this may be old/incorrect info), DC is standing by their law in banning semi-auto handguns (calling them machine guns), but revolvers will be allowed. Residents must select the revolver they want from a dealer outside DC, record the serial number, transfer it to a DC dealer, and from there it gets registered with the DC police. Bottom line, the gun has to be registered before the resident can possess it.
Again, this may be incorrect info, as I don't recall where I read it. I think it was in the newspaper. I remember there was something about renewing registration every three years, or something like that.