Even the musket wasn't the most advanced weapon of its time. The air rifles and the Puckle revolving machine gun, both of which held more than five rounds, for example, were made before the Second Amendment was written. Besides, if we're going to have that argument, the First Amendment, logically speaking, should be limited solely to spoken speech.
Another thing, liberal twats who say that weapons like the AR-15, the AKS, or even the PTR-91, are "fully semi automatic short barrel assault rifles with the ability to disperse with a 30 magazine per caliber clip in half a second," and that they're too overpowered to be in the hands of civilians, these same twats are surrounded by men who carry around M4s and M16A4s, similar to how during the Great War, the Germans called the Winchester 1897 "inhumane," despite using senfgas and flammenwerfer (mustard gas and flamethrowers).
I was rambling there for a bit, but the point is, the Second Amendment is the constitutional law that protects... well, the constitution, and it says, plain and simple, that our right to bear arms shall not be infringed.