^ We also had cannon when the Constitution was written, and they were often privately owned. People even owned warships back then.
Among other snags with that idea, the Founders up-gunned as often as they could. The 1819 Hall breech loader, developed in about 1811, became US military issue and in one case were awarded
to civilian children by the government (those particular rifles are worth a fortune now).
And of course that means that any media source fancier than a hand-cranked printing press would no longer be protected under the first Amendment.
The Supreme Court ruled under Heller that the 2nd Amendment protects the right to commonly used arms, those typically chosen by the people for their own defense. The people, through the market, mark the line that the government can't cross.