Ar-15s are not assault weapons. They are very different than their "military cousins". They resemble a look but not the functionality. It's like comparing a Lamborghini and a Volkswagen bug with a fiberglass Lamborghini body on it. And the constitution says we should have the right to bear arms..... Like oc1oc2 said. Their is no restriction clause on that.
According to Congresss they are. An assault weapon is much like Congress, it is all about apperance and nothing to do with actual function.