On how lower courts interperet "Common Use"
For example, the Glock 19 (Compact 9mm) pistol is one of the most common if not THE most common handgun on the planet.
It holds 15 rounds out of the box.
Some possible interpretations:
9mm compact firearms are in common use, therefore banning that type of firearm is unconstitutional, but "Arms" applies to weapons, not their component parts, so the mag ban is OK.
The most common defensive weapon in the world comes with 15 rounds. Therefore the mag ban is unconstitutional.
The largest mag capacity of the most commonly used type of pistols is 19 (Springfield XDM 9mm), therefore a mag ban is constitutional, but the most restrictive it can be is 19 for handguns, and 30 (standard capacity) for rifles.
Then, there is the additional complication with this law that you can posess a 10 round mag, but may not load more than 7 in the magazine. Could that be interpreted as a reasonable restriction, because they aren't banning the gun, just how it is used.
This case will be very interesting.
I suspect if it is found constitutional it will end up adjudicated in 2nd circuit, where it will be in conflict with other Federal Appellate Rulings. Eventually, it will get to SCOTUS where they will rule on the matter and set a framework for "Reasonable"
The other thing that is interesting is that it is a civil action. Nobody has been CRIMINALLY charged, and it is a criminal statute.
I am pretty sure, since this law has many other flaws, that it will be changed before this issue ever sees the inside of a courtroom.
The last thing Cuomo wants is to have even the 10 round mag ban thrown out.
Additionally, as noted in another thread, NYS Supreme Court is a trial court. They can only consider matters of law particular to the case. If they find the law unconstitutional, another action would need to be brought RE: the other law, absent an appeal.