These days, gun control proponents are thrilled. They’ve successfully pressured credit card companies to change how they code gun stores, ostensibly so they can track “suspicious” purchases and thwart mass shootings.

We said before that this wouldn’t work. We’ve said it since, too.

Now, Visa is saying it.

Visa Inc. warned a new system that gun-control advocates are saying will limit mass shootings might not have the desired effect.

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The problem, Visa says, is when it processes transactions for any merchant it doesn’t have access to data showing what products consumers are actually buying. That means the network and its banking partners would have no idea if a consumer is buying an automatic rifle or safety equipment at these stores.

“We have no visibility into what items a consumer is purchasing — this is true irrespective of which MCC applies to a merchant,” Visa said in a statement on its website. Many are “advocating the use of MCCs to track gun sales as a potential tool in combating gun violence. That’s not what merchant codes are designed for, nor should they be.”

Now, Visa has gone along with this anyway, but they’re right about how it won’t actually accomplish anything.

What’s more, most “gun stores” aren’t pure gun stores. They often sell other sporting goods, such as supplies for hunting, fishing, or camping. So any data gets even more muddied by that.

However, I think proponents of the measure know it won’t work and precisely why. This is just the first step in a longer process that will likely involve pressuring companies to track individual products.

I’m not sure the companies would be willing to go that far.

Yet even if they were, I’m not sure it would do anything then, either.

Visa and its competitors are well-versed in how people use credit cards for illegal purposes. Financial companies know how to look for financial crimes. They know what the patterns of behavior are and know when to alert the authorities.

So far, we haven’t seen any mechanisms by which Visa or another company could identify a suspicious firearm sale. After all, most mass shooters have precisely one gun that they use. How can someone buying a gun in and of itself be suspicious when thousands are bought every day and there are nowhere near that many shootings?

At the end of the day, though, the fact that Visa is telling people that this isn’t going to work is particularly telling. We know it won’t do what proponents are saying and now even one of the companies tasked with tracking this information is saying it won’t do what they’re saying.

You’d think that they’d get the message, but proponents of this measure aren’t interested in listening to it.

My prediction is that we’re not likely to see any appreciable difference in the frequency of mass shootings as understood by most of the country. It won’t make much of a difference at all.

Yet I also figure they’ll use that not as a case of getting it wrong, but instead use that failure as evidence they haven’t gone far enough.