Well, the Weathermen kind of ended the whole "walk into the general store, emerge with enough TNT to wipe out a building" era.
Since 1927 care to note how many were killed by explosives in a school attack?
I count 5 in 1959 and none since the US stopped handing dynamite out to anyone with a "tree stump" to blast.
There are indeed, many ways.
And, as JD points out, nothing to prevent the home gunsmith/tinkerer from converting almost any rifle to full-auto.
But by an large one of the most characteristic features of the mass-student-killer is their apathy towards innovation and their preference for using a credit-card as their sole means of self-arming.
When they do get innovative, they tend to get over-ambitious and stupid. Remember, Columbine was not a "successful" shooting, it was a failed bombing; one in which neither killer were to set foot inside the school.
The Donald seems to think that school shooters are cowards who would be deterred by an armed response. And yet so many intend to commit suicide on their own or by cop that it seems foolish to propose that fear of return-fire could've deterred the bulk of them.
But folks seem to ignore the notion that this class of terrorist appears to avoid anything that doesn't involve arming themselves through retail.
Yes, the political terrorists prove that innovation and home labs will find a way around a retail ban. But if we just eliminate the lazy and unimaginative misanthrope from grabbing a terrorist weapon with their skittles, maybe it might do something.
An added incentive, is the likelihood that the alternative requires a degree of competence which has caused many a would be murderer to blow themselves up. ( Not a bad end even if it does rattle next door neighbor Dustin Hoffman. )