The Constitution for the United States of America is a contract of consent by We the People to form and administer a representative republican system of federal governance among the many sovereign States in union. It is by our consent and within the limitations of the Constitution that we allow ourselves to be governed.
Included in that consent decree are Amendments that describe the some of the rights of the People and the rights of the States. The Second Amendment clearly states that the "right to keep and bear arms shall not be infringed." How can it be more plain than that? Laws that infringe on the rights of the citizens to keep and bear arms are by definition unlawful. Now some will say that it is up to the States then to make laws regarding gun control. Not so fast!
The Tenth Amendment to the Constitution also makes it clear that those powers not granted to the federal government and not prohibited by the Constitution are reserved to the States and to the People. Because the Second Amendment clearly prohibits restrictions on weapons (arms) that means that even the States cannot enact laws that infringe on the People's rights.
I have heard mention on this ongoing debate about gun laws, "Well that doesn't mean that anybody can buy an cruise missile or a tank. Actually, it does mean that! Yes, if you can afford to purchase and maintain it, you have a right to own and keep it.
All of this gun talk in the wake of these tragic shootings at cinemas and schools is knee-jerk reactions to a problem that has nothing to do with guns at all. But that is a topic outside of the Constitution and the limits it places on government involvement into the private lives of citizens.