>>720363983
You may be thinking of the Port Arthur Massacre.
tl;dr, one guy had a schizo breakdown, killed his parents, hopped in the car, drove down to Port Arthur, and just started shooting motherfuckers.
Right after, the government enacted strict gun control laws (yes, you CAN still get a gun here, americans, but "I don't feel safe" and "I just like guns lol" isn't a legit reason to get one), and also offered a "Gun Buyback", where you could take literally any gun into a handin location and get paid cash upfront for it, no matter how old, busted, jank, or handmade the gun was.
Some biker gangs made absolute fucking bank off it by handing in all their shitty popguns and slamlocks they'd built.
https://en.wikipedia.org/wiki/Port_Arthur_massacre_(Australia)