You’re really getting into semantics there. Yes they’re banning rifles (or probably just firearms, though I don’t want to see what a pistol firing this would do it’d be a dumb thing to leave out). Because we regulate firearms not ammunition.
The thing is the standardized dimensions of this caliber, as in the dimensions of both the bullet and the barrels and chambers that safely fit it. Were designed and set before that was the federal maximum. And without regard to it. The barrels did not become .50 across the top of the rifling to qualify, it qualified as is. I don’t think there is any difference in how that is measured for these vs anything else.
It was not designed with any regard to a federal standard, or defeating it. It was designed, and when the federal standard came along it qualified. And there it stays.
It is very common for a bullet to be very slightly wider in diameter than the barrel it goes into. Specifically for it to engage the rifling properly.
You’ve got it backwards. The bullet is not able to fit in the barrel despite being larger, it has to be larger to fit the barrel. And people do not pursue these because they are bigger than the regulation allows by a quarter millimeter.
People pursue them because they are the biggest thing allowed. They were not created to be the biggest thing allowed.
Reclassifying them federally on the basis of that .01" difference is something people have proposed for restricting these without the difficulty of legislation. And broadly changing the way we measure bore, or looking at the ammo or chamber instead of the barrel has been as well. States are using that standard in part as the basis for their bans, and that is to some extent useful to prevent people from making a near identical round with a different name.
But crossing that line does not neccisarily ban it federally. It simply makes it something you need a federal fire arms license and tax stamp for, those are open to civilians. It is more restricted, but such things are still available and legal on the federal level.
Frankly that hasn’t really be a particularly fruitful avenue for restricting things, and that .01" isn’t going to result in a round that’s any less powerful. The danger here isn’t exactly how wide that bullet is, but the Jesus god look at that dude’s face level of powder behind it. The specific bans some states have adopted are better, they can’t simply be rolled back by a shift in administration. But there probably needs to be some other, broader metric here beyond that. Like powder charge, bullet weight. An overall lower cap in diameter.
Similar to how we hear about the complications around which bit of a gun is legally the controlled part. And how a shift in that within regulatory agencies could change things without pushing a law through. It might tweak some stuff on certain edge cases. But what works a hell of a lot better in other countries is controlling, serializing, and restricting/registering more parts of the gun.
The problem here is the regulatory framework that allowed this. Not that some one found an end round on something effective.