I did the other day. Specifically I had thought my Mossberg 590 was a 'Virginia Assault Weapon' as defined by 18.2-287.4
It shall be unlawful for any person to carry a loaded (a) semi-automatic center-fire rifle or pistol that expels single or multiple projectiles by action of an explosion of a combustible material and is equipped at the time of the offense with a magazine that will hold more than 20 rounds of ammunition or designed by the manufacturer to accommodate a silencer or equipped with a folding stock or (b) shotgun with a magazine that will hold more than seven rounds of the longest ammunition for which it is chambered on or about his person on any public street, road, alley, sidewalk, public right-of-way, or in any public park or any other place of whatever nature that is open to the public in the Cities of Alexandria, Chesapeake, Fairfax, Falls Church, Newport News, Norfolk, Richmond, or Virginia Beach or in the Counties of Arlington, Fairfax, Henrico, Loudoun, or Prince William.

I had thought that because the 590 can hold 8 rounds of 2 3/4" shells in the magazine it was illegal to carry without a CHP where I live. Where I went wrong is that the 590 has a 3" chamber and only carrys 7 of the longer shells, meaning it is legal. Not a major issue really but one of those 'thats cool/ I'm an idiot" moments.