Montana is also the state that tried to pass a gun law that didn't require federal registration if the gun was made, sold, and used in Montana. Federal courts struck that one down.
Honestly, when reading about that, I find the panels reasoning of: "Circuit panel unanimously ruled that Congress could regulate the internal manufacture of firearms within Montana because the creation and circulation of such firearms could reasonably be expected to impact the market for firearms nationally."
Seems a bit of stretch if you ask me. I am not sure I would call that interstate commerce.
https://en.m.wikipedia.org/wiki/Montana_Firearms_Freedom_Act