AR-15s

[Undertoad]

how do you stop mass shootings? Now.

To be fair, include in your question "and not have them turn into something else," i.e., mass exploding, mass poisoning, mass drowning, derailment, large scale panic, etc. Assume that the potential shooter, when denied the opportunity to shoot, does not lose the will or insanity required to set off a murderous event that kills many.

We shall recall that enormous damage that can be done with a boxcutter, if one is motivated and clever. Or fertilizer and fuel oil. Actually, thinking that a rifle is the simplest way to effectively pull off such an event may be a lucky cultural meme on our part. In other parts of the world, they explode people. We should be so lucky that it doesn't catch on.