California has a ban on 30 round standard capacity magazines (which they dishonestly call "high capacity").

But, if you have a an AR15 in .50 Beowulf caliber, then that same magazine holds 10 rounds, and is a 10 round magazine.  Even if you could put 30 rounds into it in 5.56mm.  So, call it a ".50 Beowulf magazine," and it's legal.  Call it an "AR15 magazine" and it's not. Even if it's the same magazine.

If you are not a professional in this field, and pass a law, we who are professionals will find a way around it, and will.

Because fuck you, that's why.