The violent crime control and law enforcement act of 1974 made what activity a federal crime?

The correct answer is Juvenile possession of handgun ammunition

Basically, you could buy ammunition even if you were a kid in time before 1974. You wouldn't be able to buy a weapon, but you would be able to buy ammo, so kids would steal guns from their parents and buy ammo cheaply since it's available in any bigger store and then they would do various things with the loaded guns.