You’re right. They won’t imprison gun owners. They will simply destroy them economically with fines, seizures, loss of employment, etc.
That's why they had such a hard-on for Florida's "Stand Your Ground" law.
The part the news media NEVER talked about throughout the entire Trayvon Martin Show is that SYG confers immunity from civil prosecution so long as there's not criminality on the part of the defender.
Under the new law, they have no way to "punish" the "bitter clinger" for defending himself with appropriate use of deadly force.
It's always been the liberal way: if they can't throw their enemies in prison, they destroy those enemies financially in the courts.
If the feds try that, it will be time for the states to bar the door on such tyrannical encroachment, and protect their own citizens by refusing to comply.
As someone upthread said, the states will be forced to arrest any federal agents within their borders, and escort them to the exit.