You wouldn't buy case-quantities of ammunition in the first place.
Seriously.
A few years ago, I read a report on crooks and guns, which contained the following interesting bits:
1) Criminals are frequently arrested with guns that are NOT loaded to capacity. And it isn't because they just fired a few shots while committing a crime.
2) Criminals are frequently arrested with guns containing mismatched cartridges.
3) Criminals rarely practice with their weapons. This may explain their abysmal marksmanship.
4) Criminals are frequently arrested with guns that are in poor condition.
From this it is clear that attempts to limit the purchase of large quantities of ammunition are aimed at citizens, not criminals.
It sounds like the criminals are generally low I.Q. if some of them can’t even figure out to match the ammunition caliber with the gun. Not too surprising. But the proposed legislation we know has nothing to do with restricting the activities of criminals.