Yes, you can own them. There are some restrictions on carrying a gun with them installed in public in some cities and counties without a CPP.
§ 18.2-287.4. Carrying loaded firearms in public areas prohibited; penalty.
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.
The provisions of this section shall not apply to law-enforcement officers, licensed security guards, military personnel in the performance of their lawful duties, or any person having a valid concealed handgun permit or to any person actually engaged in lawful hunting or lawful recreational shooting activities at an established shooting range or shooting contest. Any person violating the provisions of this section shall be guilty of a Class 1 misdemeanor.
The exemptions set forth in § 18.2-308 shall apply, mutatis mutandis, to the provisions of this section.
(1991, c. 570; 1992, c. 790; 2003, c. 976; 2004, c. 995; 2005, c. 160; 2007, c. 813.)
The question is if you can afford them. At $50 for the Ruger factory ones, they aint exactly cheap. And only the Ruger metal mags are worth it. Every other brand seems to suck.
You might want to try some of the new Tapco polymer mags. I've got three and like them. There have been reports that they don't work, but I think that might be because the spacing is tight and bullet weights above 55gr tend to drag the noses against the front of the magazine. I haven't tested it though. My Tapcos work great with 55gr Remington UMC.
The 30 round mags are cool, but I think the 20-round magazines are a bit easier to handle and thus probably more practical, especially if you're shooting prone or on a bench. Maybe for SHTF the 30-rounder's a good idea.