Unless you can prove the mags are pre-ban, you run the risk of illegal "importation or possession". Even with good proof, some LEO's would seize them anyway, just because.
I would leave them home if you can.
Obviously no one plans to get stopped, etc. Some people here do use their brains, but some don't, they just "do policy" as blindly as some TSA screeners. And some LEOs are quite uninformed about the intricacies of CA gun laws, what really is legal.
