The law relating to firearms in the United States varies from state to state and is independent of, the existing federal firearms laws.  Sometimes, the state law regulating firearms are broader and sometimes more limited in scope than the federal law.  Some U.S. states have also created the assault weapon bans.  These state level bans vary significantly in their form, content, and level of restriction.  

The state laws specify that firearm license-holders are subject to the firearm laws of the state they are in, not the state in which the permit was issued.  There also exists the concept of reciprocity between states for certain licenses, such as concealed carry permits.  These are recognized on a state-by-state basis.  For example, Arizona recognizes a Nevada permit, but Nevada does not recognize an Arizona permit.  Some states do not recognize out of state permits to carry a firearm at all.  It is therefore important to understand the laws of each state when traveling with a handgun.