I'm stationed just down the road on Ft Belvoir. From my experience in general FIrearms are not permitted on most posts. I may be wrong about Ft Myer but i know its strictly prohibited on Ft Belvoir unless you happen to live in family housing on post. Even then you cannot carry you can only transport on and off post to go to the range and you have to get your Commander to sign off on a sheet allowing you to register it with the MP's. Fort Drum and Fort Gordon were the exact same way.