Wherever I as Citizen want to draw it (for me.) In reality, your income cuts off what you're going to buy. Can you afford a $75,000,000 fighter aircraft? I know I can't. When the BOR was written citizens could own cannon, mortars, etc without restriction.
I am sorry, I do not want every rich kook in my neighborhood to own cannons. It serves no useful purpose. Possession of arms is important to defend your home and family from criminals. It is not meant to fight the US Army. In places like Chicago & New York city, poor people are most subject to being victims of home invaders and robberies. And those are exact places where it is very difficult to own a firearm. That needs to change.