You'd have to collect the guns for it to be effective. There are over 300 million generally unregistered firearms in private possession today, that might get a little tricky.
Any sensible implementation would be a phasing-out rather than a single sharp transition. It's not going to be like Sweden changing which side of the road they drove on overnight.
>Any sensible implementation would be a phasing-out rather than a single sharp transition
Many Americans already believe that gun control legislation is part of a program to phase out gun ownership and undermine the Second Amendment - and that's why they're stockpiling guns in expectation of an inevitable civil war. It's never going to not be tricky in the US.
Anything approaching what the rest of the world considers "sensible" gun control in the US would first need a massive cultural shift to take place, or an acceptance of protracted guerilla warfare as a consequence.