we are to take the post offices arguments against guns on postal property then I cant see why that same logic wouldn't or couldn't be applied to every ounce of federal property.
It's not that the property is owned by the guvmint, the wording is actually "federal facility".
The term "Federal facility" means a building or part
thereof owned or leased by the Federal Government, where Federal
employees are regularly present for the purpose of performing
their official duties.
18 U.S.C. section 930
During one of the firearm classes I took, a lawyer said he believed that a ranger station or National Forest visitor center would also fall under this definition out to the parking lot.