I don't know what country the guy was from, but some American veteran mentioned that's what they did when they took over any city/town.
The foreigner laughed, saying while the Americans went door-to-door, the ever-efficient Germans just stayed at the headquarters and let it be known that anyone who did not turn in their gun would be executed. 100% compliance, or the owner vanished and went to the Resistance.
If it ever came to confiscation here in America, they wouldn't go door-to-door, just issue an "armed and dangerous" warrant and let the Highway Patrol pick 'em off one at a time. No muss, no fuss.