If one wants to ban guns in the US, there are three big practical problems with doing so:-
1. A lot of people there see it as an intrinsic right of being human. Their response will be violent.
2. The two bordering nations are Canada and Mexico. Making gun smuggling almost as easy as drug smuggling. (+ unique geography makes it even easier)
3. There are a lot more practical uses for guns than in most other developed nations. Large areas have genuine wildlife threats quelled with guns, and others rely on hunting for food.
It would still remove the easiest method of acquiring guns illegally, which is by stealing, borrowing or buying them from someone who obtained them legally, but it is still worth considering the US as a special case.