There has to be options somewhere, it's already been said that it's far too late to disarm the nation, the amount of firearms available would make outlawing them pointless, there'd still be hundreds of thousands in circulation easily.
Just to shed some light on what is readily available to the average joe in the US and let us all take a step back to consider this for a moment.
2x .223 Remington AR-15 variants. A military styled assault rifle which is legal, Typically a 30rd STANAG magazine. They can be used with a drum magazine that holds up to 100 rounds. An AR-15 is basically a continued spinoff of the widely used m16 assault rifle.
https://en.wikipedia.org/wiki/Sandy_...chool_shooting
https://en.wikipedia.org/wiki/2012_Aurora_shooting
https://en.wikipedia.org/wiki/Geneva_County_massacre
Naturally there's more with different or the same Assault rifles. This is why I haven't bother mentioning handguns. You want to be starting with the most lethal of their arsenal. No civilian should be allowed to legally own an assault rifle. Bullets kill regardless of their size and what they come out of. But allowing people to arm themselves with .223 rounds is absolutely mad. Weapons of absolute accuracy and maximum damage.