As was already said above by other posters: For a normal AR, the easiest path is to remove any forward grip, flash hider or other "evil feature", and replace the pistol grip with a fin grip that doesn't allow the thumb to be wrapped around it. If you insist on keeping the pistol grip, you need to get one of the mag locks that requires opening the action to reload the gun.
No magazines >10 rounds are allowed at all (with tiny exceptions for rimfire tube magazines on lever actions). Do not bring them into the state.
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... and reload ammo instead of mail order due to THAT new law, correct?
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You don't need to reload. You can go to any gun store and buy ammo there; there is some extra paperwork (fundamentally a background check), but ammo is widely available. Even some Walmart stores still stock and sell ammo (fewer than before, but some still do).
You can also get an 03FFL (the federal curio and relic collector license) plus a California CoE (an annual permanent background check that includes fingerprinting), and that allows you to mail-order ammo directly to your house. Or you can have mail order companies ship to a local gun store, and then pick it up there (with the background check done on the spot, for a fee). Not all ammo dealers are willing to participate in either of those, and few gun stores are willing to accept mail-order shipments for stuff they have in stock.
In a nutshell, ammo is still widely available, but it got more expensive (except for what Walmart happens to carry) and more hassle to buy.