CA Laws are complicated but there is a way to legally use large cap mags. It breaks down like this:
There are three ways to get an AR in CA:
1)
Registered Assault Weapon - You had it before Y2000, registered it before Y2001. No new registrations so if you don't already have one of these you're not getting one. Can be configured as evilly as any free-state rifle, and will appear quite normal.
The next two ways apply only to receivers that are not on the "List" of evil brands/models, hence they are called Off-List Lowers or OLL:
2)
Fixed Magazine - All the evil features, except you have a 10 round mag limit (for appearance you can use a 30 rounder blocked internally for 10 rounds), magazine can only be removed through the use of a tool, law says a bullet is a tool, hence the various "Bullet Buttons" that have been invented and marketed, each design more ingenious than the last. Despite being limited to 10 round mags these also can look exactly like a free state rifle.
3)
Featureless - no evil features, not even the pistol grip, but you get to use legally-owned large capacity mags and drop them with your finger. There are four products on the market right now to address the pistol grip issue, the latest is the Exile Machine Hammerhead Stock Adapter / Grip. These rifles while they can shoot large cap mags currently look somewhat different from a free state rifle, due to the pistol grip issue. Efforts are always underway to try to make these look as close as possible to a free state rifle but it's a challenge to get around the pistol grip. Some shooters are even using adjustable stocks that are riveted or pinned so they can't adjust.
Here's a really good site to interactively help you determine if your evil rifle is legal in CA:
http://calnra.com/cgi-bin/flowchart.cgi
Exile Machine is working on a half dozen additional CA-compliance products. We're targeting Featureless right now because there's room there for growth, and the ability to use 30-rounders is appealing to customers. Eventually we'll have products for both Fixed Mag and Featureless. Ultimately we hope the whole damn CA Assault Weapons laws get stricken from the books and we can get back to doing what we do best, manufacturing nylon curtain rods.