It is not the middle of the night, “night of the Long Knives” type operation that people need to worry about, for the simple reason that there are too many guns to be policed up that way.
In fact, outside of a natural disaster, where people are forced to evacuate, followed by a slow and methodical, house by house search for guns, it is pretty hard to do it this way.
What the government would first do would be to locate and confiscate guns based on gun dealer records and gun check records, “Oh, were we supposed not to keep those records? Well it’s a good thing we did!”
They would prioritize a methodical sweep by starting with gun dealers, taking their inventories, and then they would focus on people who had accumulated arsenals of weapons, and weapons of unusual capabilities, like .50 caliber rifles and above.
The manpower needed for confiscation is staggering, even over the course of years, so the government would need a willing “army”, not the military nor local or state police.
The Nazis used the “brownshirts” Sturmabteilung, many of whom were criminals flushed from the prisons, given uniforms, and told that as long as they followed orders, they could pillage from the citizenry. In that there are some 2 million plus prisoners in the US, the government would most certainly consider this option.
They would have to have a core of paramilitary trained thugs. So much of this would be simplified if they could be issued drugs to make them obedient, which is not impossible.
The trouble is that the current administration, and many Democrats, ignorantly thing that those that join the military are incompetent, stupid and brutish, and yet will obey orders, no matter who gives them. So they imagine no difference between them and the paramilitary thugs they would need to confiscate all guns.
Likewise, they hold local and state police in the same contempt. Yet assume they will carry out federal orders without hesitation.
Bottom line, outside of a super major disaster that devastates the US, this is not going to happen anytime soon.