The Constitution doesn't "only talk" about militias, and doesn't mention muskets (or any other specific type of arms) at all. Indeed, muskets weren't even "state of the art" when the Constitution was written, so a belief that the Founders were only referring to them would definitely seem to be mistaken.

To me (and six Supreme Court Justices) the Constitution says you have the right to keep (own) and bear (carry) arms (firearms) and because of this, laws that put an undue burden on this right are unconstitutional.