Here's some info on FOPA and how it came to be.
re: the interstate transportation section which is actually only one small part of the entire law. The problem arises when L/E doesn't realize this even exists or interprets it wrong.
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2. Interstate Transportation of Firearms
In response to reports of hunters being arrested for firearms law violations while passing through a state with tight controls,[488] FOPA's drafters inserted provisions to offer protection for such travel. S. 49 as introduced provided that any provision of state or local law "which prohibits or has the effect of prohibiting the transportation of a firearm or ammunition in interstate commerce through such state, when such firearm is unloaded and not readily accessible, (p.677)shall be null and void."[489] On the Senate floor, an amendment was accepted which changed this in two respects: (1) the protection was extended only to persons not prohibited by the Gun Control Act from transporting, shipping or receiving a firearm; and (2) the provision that an infringing law was to be null and void was dropped in favor of a simpler declaration that the transportation was allowed notwithstanding any such law.[490] The rationale for the former change should be apparent. The rationale for the latter was a concern that, if the provisions that "have the effect" of inhibiting interstate transport were declared "null and void," entire sections of state law might be challenged and voided as to all purposes.[491] In this form the provisions passed the Senate,[492] and an identical provision was inserted in the bill that passed the House.[493]
Upon transmittal of the House bill to the Senate, the Senate passed both it and an amendatory bill, S. 2414, which greatly affected this section. S. 2414 narrowed the right of travel by providing that it was a right "to transport a firearm for any lawful purpose from any place where he may lawfully possess and carry such firearm to any other place where he may lawfully possess and carry such firearms"; moreover, both firearm and ammunition must not only be not "readily accessible" but also not "directly accessible from the passenger compartment."[494] The restriction to transport to and from areas where the arms might be lawfully possessed was apparently a counter to criticisms that the bill might otherwise bar arrest of the owner in his own state, under that state's laws, if he argued he was beginning a permitted transportation.[495] The second change was intended to rule out carrying in a glove compartment,[496] which the Senate (p.678)reports had indicated would qualify as "not readily accessible" under FOPA.[497] On the other hand, S. 2414 seemingly widened the allowable transportation by requiring, not that it be "interstate commerce," but that it simply be "from any place" of lawful possession "to any place" of the same.[498] The House passed the Senate bill without amendment.[499]
Enactment of S. 2414 does leave some questions unanswered. Fortunately, its late origin has given us a legislative history adequate to address most issues.
Accessibility
The first question is obvious: what is "not readily accessible"? We can easily discard the horrible hypotheticals raised during the House debates on FOPA, that a briefcase behind the seat would meet this test,[500] or that "inaccessible in most cases probably means concealed."[501] In practical terms, the requirement of inaccessibility is essentially subsumed in S. 2414's requirement that the firearm be stored outside the passenger compartment. If storage in a locked glove compartment was sufficient to meet the accessibility test, as the legislative history clearly indicates,[502] the (p.679)required storage outside the passenger compartment should clearly suffice.
Purposes
A second question is likewise obvious. For what purposes may the transportation be undertaken? FOPA itself had no requirements relative to the underlying purpose.[503] Opponents of FOPA criticized this lack,[504] but did not carry the day; a House amendment that would essentially have required that the transportation be for defined sporting purposes was decisively defeated.[505] S. 2414 does insert a purpose requirement, but one far broader than that proposed unsuccessfully in the House; the transportation may be for "any lawful purpose."[506] The omission of "sporting" or its equivalent is apparent and would suggest that the transporting party may intend any lawful purpose, including self-defense, at his or her destination.
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Here's a link to the entire somewhat dry story that the above is a swipe from..
http://www.guncite.com/journals/hardfopa.html