[NoImmatureAdHom]

I remember the word "regulated" back in the day does not mean "regulated" like the FDA regulates foods, it means "regulated" like we still use it for regulating a mechanical watch. "To adjust (a mechanism) for accurate and proper functioning."

[sophacles]

And you regulate a militia by making sure all the bits work together, for instance by standardizing weapons and ammo.

This is also a great argument for licensing - proving that you know how to properly work and use a gun seems like perfect militia regulation (in the proper functioning sense).