That is, they are threatening that if the Supreme Court rules disfavorably to an individual right to keep and bear arms in the Heller case, they will see that as a violation of their contract with the United States and reserve “all usual rights and remedies under historic contract law if its Compact should be violated by any ‘collective rights’ holding in Heller.”
The resolution, which has only been signed by some of the legislators, declares that “any ‘collective rights’ holding in D.C. v. Heller will violate Montana’s compact with the united states, the contract by which Montana entered the union in 1889.”
This, along with The Montana Sovereignty Protection Act and the state’s stringent opposition to Real ID, make it quite an attractive place for libertarian-leaning folks to reside.

Nice alliteration! Oh, and go Montana!
Just one problem — Montana was already US territory by right of the Lousiana Purchase. The only effect this dumb act will accomplish is to deprive Montana of its congressional delegation and put a few nut jobs in jail. And which whom was this “contract” made? With Congress? All they did was admit Montana. Montana accepted this admission the moment it ratified the US Constitution. All this reminds me of the “Republic of Texas” thingy a few years ago.