Here's a video from the National Shooting Sports Foundation (NSSF) that makes the case that bans on high capacity magazines are illegal.
They base this on the concept of items in common use cannot be banned.
They cite there are (conservatively) ONE BILLION (that's 'BILLION' with a 'B') high capacity magazines in just the CIVILIAN community.
The video is a bit under 9 minutes and pretty easy to watch.
https://www.youtube.com/watch?v=MIAZjItWsoE