That is not true. If it’s pre 1898 it’s antique, beyond that it is classified as a destructive device and has a whole bunch of red tape. Anytime you see words $200 tax stamp it isn’t easy to get.
And even a pre 1898 cannon is going to cost you $8k+ for a rusted out POS that will explode if you try to actually fire it.
We wish they were that cool, the inventors of the modern mile were more concerned about land measurements. A square mile is 640 acres. Which neatly can be cut into quarters 3 times. 160, 40, 10.