I agree, I cannot see physical resistance over gun laws by state level actors. Might a small local department or members of such go 'rogue' so to speak. Perhaps. They would not be supported.
The closest we have come to this, is the armed resistance of some citizens and local authorities to the Fugitive Slave Laws and slave catchers. I doubt a Federal gun law would have the same moral outrage. We certainly didn't see it in the past Federal bans or now state bans (and in some states there are certainly committed pro gun folks).
I also agree, and have said, that the utility of such pronouncements and laws are to demonstrated the electoral consequences of bans and perhaps give support to judicial actions. One might equally ask if some Federal future actor (a Jeff Sessions clone) might want to take action against local marijuana laws, would you expect actual physical resistance. NYS is legalizing marijuana. My area has plans for a giant farm, processing plant in old steel mill land - and we need the economy boast. I don't expect the NYS troopers, National Guard, Buffalo police to start an armed confrontation with a future Jeff Sessions. Cuomo on a tank! That would be run to see.
The antigun politicians need to see that they can lose swing districts over gun bans on the Federal level. With Congressional margins being so small, every district counts in the House.
Like I said, it is more to protect Missouri residents from illegal confiscations on otherwise legal firearms.
Again how, a Federal confiscation is legal and trumps state law. Beside a howl of outrage, how does it protect?
The AFTE shows up at your house. Give me your brace and bump stock. What's the state's play?
