Start with people who pose danger
As for limiting the number of rounds in a magazine, insane people are not stupid. They will just carry more magazines.
Does anyone ban hammers because they bent the nail?
How many crimes are committed with illegally obtained guns?
How many people are killed by cars? They don't go by themselves, do they? Ban them! I think we should keep incompetent people out of them.
Suppose a terrorist group attacks us. Will we be able to respond quickly enough to prevent a tragedy? Seems to me that no such group would dare to try it because of an armed public.
Are people allowed to protect themselves, family and property from criminals and/or crazies? Seems to me that there are too many laws against such protections in many states.
How about finding the mentally incompetent and those who are predisposed to mental problems! Is banning guns easier? Cheaper?