The 2nd amendment applies to all bearable weapons, even those that did not exist at the time of writing (Caetano).
That seems to conflict with Miller though? A short barrel shotgun apparently wasn’t standard military issue so it wasn’t legal for possession?
The Second Amendment protects only the ownership of military-type weapons appropriate for use in an organized militia.
The “double barrel 12-gauge Stevens shotgun having a barrel less than 18 inches in length, bearing identification number 76230,” was never used in any militia organization.