2F black powder, cannon fuse and PVC pipe can all be obtained in a very short amount of time, if you were so inclined.
Was buying reloading supplies when I was 15, never got asked for ID. That may have changed, I’m not 15 any more.
My point being that it took time to assemble an whole lot of items, even in a relative short amount of time, it took effort to cut the plastic pipes and assemble them.
Don't know if he tried them out before hand but I know I would have a difficult time (but not impossible to create) a collection of such weaponry but my folks or my brothers would find out some of "my evil plans".
And I lived on a large farm with lots of buildings to hide the objects needed to create such mayhem
Of course I had two caring parents and brothers who could be assholes but did care about my general welfare when he wasn't threatening it.
Could I have done it? Maybe but no law could have prevented what a pair of attentive parents could have done in just the course of being good parents.