The whole "how many guns / how much ammunition / how big a magazine do you need" trope is nothing but a smokescreen. Notwithstanding that it's the Bill of Rights, not the Bill of Needs, I could have a million guns, a billion rounds of ammo all loaded up into 500 round magazines and what do you think I'm going to do with it? The same thing I'd do with one.
How many books do you need?
It is all nothing but a smokescreen. Evil people are going to do evil things. You might as well pass a law against the sun coming up in the morning. (Yes, I've heard rumors about Copernicus' recent hypothesis).
I find it frankly hilarious that some of the same people who tell us that we could never possibly control our borders to keep people from coming here illegally will, in the very next breath, suggest that we could do the same with guns. Great Britain can't do that and they are on an island! We can't keep people from getting cocaine and heroin, how the hell are we going to keep people from getting guns?
Most of the people who say we have to have more and stricter gun laws haven't got the faintest notion of what is already in place. All of which criminals routinely ignore. Why? Because - surprise, surprise - CRIMINALS DON'T OBEY THE LAW! But until people understand that laws only affect the law abiding, they will continue to have Utopian fantasies that we can somehow legislate evil out of existence.