I would politely disagree, it's entirely about one of the most basic issues in the constitution. It's not about a "right to buy" it's about the right to bear.
There is a specific constitutional amendment regarding the rights of the people to bear arms, some would argue that that right would include relatively unfettered access to ammunition.
Until that argument goes all the way to the Supreme court, you'll have stuff like this going on.
If a store is having it's inventory stolen, shouldn't the steps taken to alleviate that be their responsibility, not the government's?
OK, without "sand in the eyes" and all that, let me take you through the thinking of this legislation. I don't like it at all, however, I do have the ability to see more than one side to an argument - it helps you understand why and how to disagree if you fully understand what the other argument is all about.
Let's assume three things.
1) You have a non-law abiding citizen who has a gun. OK, they are a criminal, we know that and they should not have the gun in the first place. See sentence one.
2) Let's also assume that you have a place with a quantity of ammunition suitable for a variety of weapons of many kinds. Let's call this place a gun shop, but it could be a Wal-Mart or a bait shop, depending on where you are in the USA.
3) Let's assume that this non-law abiding person has access to ample quantities of cash, from any number of sources, none legal.
Now, when you or I buy a gun, we fill out the form, we do the background check, and we get our gun. No big deal. I do it all the time.
Every year, there's a list of ding-dongs who have criminal records who get caught with this trivial step. I find the whole process a little silly, but what it does it it keeps those who definitely can't buy a gun (legally) out of the stores (and onto the streets, which is a whole bigger issue that we should not take up here).
Now the same guy comes into the store, a place where if he was to try to buy any guns, he'd trip the background check...but he wants to buy 1,000 rounds of .45 ACP. Forget stealing it - he wants to buy it. What, exactly, does a guy who is not legally able to own or handle a gun need 1,000 rounds of ammo for?
And that's the path of reasoning that led to this law.
Now, the problem is, of course, that they really aren't concerned in the least with people who are legally buying ammo for their hobby, for their club, or for their personal self-defense.
While this is a defective law, the logic behind it is consistent.
There must be better ways to get to the same ends - reducing ammo getting to people who should not need it.