The U.S. already bans fully automatic guns: machine-guns have been illegal for decades. Federal law should also ban semi-automatic guns, especially those with large bullet-magazines.
All that is needed for compliance with the 2nd Amendment is to allow people who feel they need a gun to own single-shot (reload one bullet after each shot) guns. That's all anyone needs for self-defense, hunting, or any other rational purpose. That is also all that existed when the U.S. Constitution and the 2nd Amendment were written.
Why is this important?
Gun control in response to Connecticut shooting.