You won't have to go door to door. Ban the sale of guns. Ban the sale of bullets. Have a system put in place for people to get their license to keep their guns for hunting reasons. Give everyone a 2-3 year deadline to either give up their gun or get licensed to own hunting guns.
Uh, you do realize that "hunting" guns can kill people? One of the reasons the Norway killer was able to get guns was because he applied for a hunting license.
In the first 5-10 years, you will get most of the guns out of the troubled neighborhoods.
Various US cities have certain types of gun bans. Washington D.C. banned hand guns in the 1970s, but they are still a top gun violence city.
12,000 people are murdered every year.
Few of which happen in New Hampshire or Vermont, two states with the laxest gun laws. You're much more likely to get murdered in Washington, New York City, or many of the other cities with stricter gun laws.
Making a gun is a lot more complicated.
Supposedly 1/5 of guns seized in Washington D.C. are homemade to one degree or another.
On another note, the US should also keep mental hospitals open.
I think they are.