Re: A gun is involved in every single mass shooting.
AFAIK, you can't easily make ANFO anymore, because they changed the recipe of fertilizer to contain less nitrogen.
As for "doing something": anything that would be done now would only impact the (very) far out future because of the number of legal and illegal guns in circulation.
We know how good politicians are with such far-out timelines...
The sheer availability of weapons is not the only factor in reducing the number of shootings.
I live in a country where every able-bodied citizen has to join the military for compulsory training once he turns 18. Everybody who completes that training gets a fully functional, automatic assault riffle to take home and keep, in case the country is attacked and quick mobilization is needed.
Ammunition is not handed out anymore (since 2007), but that is not a big obstacle.
While murder-suicides did and do happen, but they usually involve close family.
Why is that?
Maybe because a functioning social security system exists, that doesn't leave people completely hopeless? Even criminals can have hope here (up to a point, of course).
Maybe it has to do with the amount of holiday people get, the amount of work-related stress?
Also, the amount of prescription drugs consumed is way less here (well, pretty much everywhere else but the USA has lower consumption).
I'm in favor of restricting gun-ownership (unless maybe you live in the mid-west and actually own a farm or go hunting nobody needs a gun).
But it's unfortunately only a very, very small part of the puzzle and it will only slightly reduce the problem, for a very long time: the guns will be around for decades to come.