Limit the amount of bullets that citizens can buy each year. People have a right to protect themselves, but there is no need to stock up enough bullets to go on a shooting rampage.
Limit the amount of bullets to 10 per year, for each type of gun. There is no way a person needs to use more than 10 bullets per year to protect themselves.
For hunters, limit the number of bullets used to the average number of bullets used on one hunting trip. Require hunters to buy bullets before each trip, prohibiting them from stocking up.
For shooting ranges, require that a person buy their bullets at the range. They would receive enough bullets for target practice, and would have to turn in and get refunded for the bullets they do not use.