As long as people continue to argue for creating victim-disarmament zones, free-fire zones for criminals, then criminals will continue to take advantage of them to kill people in job lots and mass murders will continue. Banning particular weapons will not stop that.
The first high-profile “school shooting” was the Texas Tower Sniper. He didn’t use any “high-power assault weapons” (the .223 used in AR and similar rifles is actually fairly weak as rifle rounds go–don’t believe what the media tells you; check the ballistics for yourself), “high capacity”, rapid fire” (one round per trigger pull is not any more “rapid fire” than a Smith & Wesson revolver and 30 rounds has been standard capacity for more than 50 years in AR pattern rifles) weapons that scares the pants of media and anti-gun pundits. He used ordinary hunting rifles. (Mind you, when the hoplophobes get around to going after them, they call them “high-power sniper guns”.)
The highest death toll school massacre in US history didn’t use guns at all. It used explosives.
The Happy Land Fire, which killed 90 people, as the name would suggest didn’t use guns at all. It used fire.
The largest mass murder in US history didn’t use guns. It used fertilizer and fuel oil. Yes, they now include “tracer” chemicals in ammonium nitrate fertilizer so that they can track the source of the material if it’s used as an explosive. How effective that would be to stop a “blaze of glory” type common in spree killings is left as an exercise for the student.
And even if guns somehow were the magic “death wands” that anti-gun folk think, you really think you can keep them away from someone determined to cause harm? The US Army has a training manual on improvised weapons that includes firearms and explosives Yes, how to make both using “ordinary” materials one might obtain at the local hardware store is described, in detail, in the manual.
It’s available online.
I have it in PDF as do a lot of other people.
The simplest repeating firearm to make (given current knowledge) is an open-block, auto-only (no select fire, no semi-auto mode) submachine gun. Some springs, some rod, some pipe in a couple of different sizes, and some sheet metal and scrap to make odds and ends, and an evening or two’s work. I haven’t done it, but I know how. (I am stopped by its being illegal. Someone willing to commit mass murder would already have proven they are not stopped by something being illegal.) I’m nowhere near unique in that.
And even if you went all the way back to cap and ball revolvers. These are not Federally regulated at all BTW, being considered “antiques”. Replicas are also not regulated. Well, there’s nothing to keep from stuffing a half dozen to a dozen such revolvers in ones belt or hanging off bandoleers (covered by a jacket, perhaps, until one is ready to shoot. (I am a writer and thinking through scenarios like this is part of what I do: “how could my character…”). “The Outlaw Josey Wales” has an awesome bit near the end where Josey (played by Clint Eastwood) draws revolver out of revolver (most “cap and ball”) from his clothing. The revolvers are empty and the “click, click, click…” change revolver “click, click, click…” change is very dramatic. (Note: I present this as an illustration, not “evidence.” There’s nothing stopping someone from carrying a bunch of “low capacity” firearms and using them one after the other.)
Or consider someone with a satchel full of single-shot zip guns–cheap and easy to make. Fire, drop, grab the next. Repeat.
Thus, no amount of disarming of innocent people will stop “bad guys” from getting the means to perform mass murder if that is their goal. The solution must lie elsewhere. But so long as people keep focusing on the specific tools used by the spree killer, we’re distracted from even looking for the real causes of the problem.