Wow...I'm not a lawyer but that doesn't seem legal. Just curious how a state can completely disregard a federal law. I can understand challenging a federal law in court like several states did with Obamacare but this is just complete disregard. They got balls...I like their boldness. 
Key words are:
...that is owned or manufactured commercially or privately in Wyoming and that remains exclusively within the borders of Wyoming.
The Federal Government, Constitutionally, can regulate
interstate commerce. ("Commerce Clause" US Constitution Article 1, Section 8, Clause 3
http://en.wikipedia.org/wiki/Commerce_Clause) Theoretically, anything contained within a state is to be regulated by the state. The Commerce Clause was stretched to the extreme in 1942 when a farmer grew more wheat than he was allowed during the Great Depression, to be used within his own farm. (Wickard V. Filburn
http://en.wikipedia.org/wiki/Wickard_v._Filburn) To make a long story short and according to my memory, it was ruled that though he was keeping the wheat for himself, he could
possibly affect wheat production within his own state which could
possibly affect other states, which would then be part of interstate commerce, therefore the Federal government could tell him to stop making extra wheat for his own personal use.
Laws such as these and other Firearms Freedom Acts passed by other states aren't really just about firearms. They're mostly about taking States' Rights back from the Federal government.
...then again, IANAL, and everything just said is worth nothing.