Unfortunately, there are nine justices on the Supreme Court who have the final authority on what is and is not constitutional, and none of us are one of them. So it does not make a hoot in hades what we think. And the SCOTUS and other Federal courts have made no ruling on magazine capacity other than they can be regulated.
The judiciary issues opinions. It’s up to the executive and ultimately us whether or not to give those opinions the legitimacy of the force of law.