It would definitely be hard to confiscate considering it would have to be military or police to do so and most would say F that. My best friend is a cop and told me it would be too big of a risk on their lives to go door to door asking for someone's weapons. I feel like quite a few would shoot upon arrival of someone trying to take their weapons.
One avenue of many it would be done is to tell the police to take every gun they find as they perform their duties.
Over time, there would be large number of guns stolen from us by the government and nobody would be going door to door.