If one is crazy enough to want to kill 6 people at a school, dying themselves in the process, there are easier and cheaper (and probably less painful) ways.
When I was a teen, we kids almost all had guns, and certainly our parents did, and security was minimal. Basically, if my P’s were away, I could have at any time easily picked the lock or broken down the door to the room where Dad kept his guns. I hardly think that if I’m gonna go kill some people, the threat of Dad being mad that I broke into his den would have any influence to stop me.
Firearms were a lot cheaper then, too, and there were no checks at all.
“Availability” isn’t the problem here.
you’re talking to a troll