I would advise you to call the CA DOJs office and talk to them. Most of the state's gun laws do not apply to non-residents. You can't carry, and can't bring in "assault weapons" either, but the prohibition on hi-cap mags doesn't apply. The hi-cap mag restriction only applies to residents of CA, not visitors. I found this out by calling the DOJ and speaking with them. I have standard mags for all of my guns here and have taken them to ranges and such as well. Even though I have been stationed here for 3+ years, I'm still just a visitor by California's legal standards. The guys at the DOJ are very helpful and willing to answer any questions you have. I have an e-mail around here somewhere from them detailing what I could/couldn't do.

Bill

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US Marine, 16 years+