Or when they simply ban possession of ALL "hi-cap" mags instead of post ban ones.
I'm guessing that if they enact such a law, the penalty will be 5 years for each "illegal" magazine.
For many Americans, that would mean literally decades or centuries in a federal prison.
When faced with such a choice, some Americans will hand over their magazines to the JBTs. Others will presume that if they're going to get 100 years in jail anyway, they might as well "live it up" from 300 yards away.
Banning 11+ round "Hi capacity" mags would be a cheap and easy back door way to effectively ban semi autos.
Like you said, that's when the 300 yard voting might begin.