I don't think they give a rat's patootie what size is the standard.
They simply want to pass legislation that an X amount of shells is not acceptable in that scattergun.
Then they will simply tweak for less and less capacity, until only single shot shooters will be tolerated, then only muzzle loaders.They simply wish to remove firearms from people like....you!
I know. I'm just not getting the hang of this "stand down and let the hoodies have it" thing, and they're not happy about that.