... that you can own a musket.
Because that is what it was refering to at the time.
Simple. No one can complain that their rights are being taken away.
Why would it make sense to take a sentence from 200+ years ago and apply it to the technology available today?
In the same way that if you have a license to drive it means you have the right to drive a regular car, not an F1 car, a tank or a fighter-jet.