Tens of thousands of illegals is easy. 80 million conservative gun owners isn't.
I've played military logistics professionally, at a low level.
/johnny
They don’t have to round up everyone. And not right away.
Look at the early post Czarist Russia. Many regions had more guns per capita than the USA. Most people turned them in when the State made a few messy examples and carted people away. The rest hid them. There are old Russian jokes about going out to “oil” the flowers. All the small arms in the world don’t matter much if (as you said) the logistics are not there.
If tomorrow, they started arresting every tenth TEA party member (or hundredth) most of the rest would fade.
Heck, the US military kept the peace in the South after the Civil War by doing such things. Kill a few here and there, and the rest will calm down. Cart the leaders away and the sheep will scatter.