It wasn't federal property, it was property held as surety by one State to ensure the performance of the other States to the compact.
When the northern States failed to perform, the Notice of Secession caused the property to revert to the States that initially held it.
In actuality, it was being unlawfully occupied by federal forces, and that's why it was fired upon.
Neither of these rules has been adopted. Each State in ratifying the Constitution, is considered as a sovereign body independent of all others, and only to be bound by its own voluntary act. In this relation then the new Constitution will, if established, be a federal and not a national Constitution.
Federalist, no. 39James Madison, 16 Jan. 1788
That’s kind of moot now, because there IS Federal real estate at stake today. Good luck to Texas if it grabs all those post offices, etc.