A lower is not registered. Also, while some Knight Armament lowers are named, unless it is a semi-auto firearm, it does not apply. Such a lower which is a single shot, bolt action, pump action, etc. would not be banned, but it could cause you problems.
If you moved from another state, you would not be required to report it, unlike handguns. If it was a semi-auto rifle, then it might be banned and illegal to have in CA.
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