The sheriff can't block federal gun control. The case you cite in no way supports this very broad proposition as you claim it does.
The holding of the case is congress has no authority to force the executive branch of state governments to enforce federal law. So they can't compel the sheriff to assist them but the feds can and will enforce federal law.
We have always understood that even where Congress has the authority under the Constitution to pass laws requiring or prohibiting certain acts, it lacks the power directly to compel the States to require or prohibit those acts.
New York v. United States(quoted in Printz)
The court in Printz went on to say that requiring states to enforce federal law is not at all distinct from compelling a state to make policy.
As a community we really need to avoid crack pot theories with no basis in law.