These are very popular recent gun control arguments, I think they're unfortunately a bit misguided. What difference does it make if someone buys ammo on the internet or goes to their local Walmart (one of the biggest retailers of ammunition in the nation)? It would be far easier for most to buy ammo locally than wait for it to arrive from the internet.
If someone is skilled with any sort of firearm, the entire reloading process can literally take seconds. The idea that the capacity of a magazine somehow makes a weapon any more dangerous is one of those things anyone experienced with firearms shakes their head in confusion at. In all honesty, higher capacity magazines actually make guns far more difficult to effectively handle, and drastically reduce the accuracy and reliability of most weapons. It's the reason the military themselves chooses to use standard sized magazines in all of their weapons, and most competitive sharpshooters choose weapons with smaller capacities.
A gun, in and of itself, is a dangerous weapon. The caliber, capacity, or location in which you can buy it does not make it any more or less dangerous. I've grown up around firearms since a young age, and am as avid a shooter or supposed "gun nut" as anyone, but I think laws designed to address the above issues are besides the point, and will not stop tragedies like what's happened today in any way. I absolutely agree that massive work needs to be done on gun control, and I think most of the efforts need to be placed on keeping guns out of the hands of those who would do things like this, not efforts that don't in any way make the said weapons less dangerous.
There's a ton that can be done, it just requires the ridiculously partisan country we live in to finally make concessions. The silly "nothing should be done" or "all guns should be outlawed" crap coming from either side is juvenile and unproductive. Everyone knows there's a problem, we know no one wants to upset the precedent set by the Bill of Rights, so do something about it inside of those constraints. Boo hoo if the government's costs with firearm and ammunition manufacturing companies will go up. Boo hoo if gun owners will have to take far more steps and time to acquire weapons and ammo. Freaking do something effective.
That all said, it still crushes me that these things continually happen in the US. What's wrong with our society and culture? Why does this stuff not happen in other countries where firearms are just as readily available? How could people do these sorts of things? It's horrible.