Probably not what you wanted to hear, huh?

http://library.municode.com/HTML/102...AIV_D2_s38-130

Sec. 38-130. Assault weapons.

(c)
Specific weapons not included. As used in this section, assault weapon does not include any of the following:

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(2)
Any firearm that uses .22 caliber rimfire ammunition.


Again, though, DPD has been known to disregard the law, even for nonresidents transiting the city, in contravention of subsection (e). The arrangement usually looks like "forfeit the gun and we won't prosecute".