While open carry is legal in Virginia in most public places, carrying a rifle (or a pistol) with a larger capacity magazine may get you in hot water.
Before carrying any weapon in public, it's a good idea to check out the state code to make sure you know what's illegal. Go to this link and do searches on keywords like "gun", "firearm", "magazine", etc.
http://leg1.state.va.us/000/lst/LS728775.HTM
Also, if you have some time, do some research on things like lawful use of lethal force case law and such. There are lots of places and people who can steer you in the right direction.
Since you are asking about a rifle, here is a link to the state code, and an excerpt that may concern you:
http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+18.2-287.4
>§ 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.)