Some useful distinctions, I think:

* Regulating using a gun
* Regulating carrying a gun
* Regulating owning a gun
* Regulating parts of guns
* Regulating tools that can be used to make guns
* Regulating the information necessary to make guns
* Regulating the information necessary to make tools that can be used to make guns

Bonus distinction:

* Substantial noninfringing use
* Substantial non-horrific use