If you are moving to Califonia, you can bring a .50 caliber rifle into the state, but first you have to get a permit for it from the Department of Justice. The law states that you have to turn the rifle over to an FFL Dealer while the paperwork is processed. Personally, I would not do that, because if, for some reason, you were denied the permit, then there is the possiblity you would not get your rifle back. I would keep the rifle out of state until I got the permit. That way if you were denied the permit, you could make arrangements to store the rifle out of state or sell it. I would contact DOJ prior to moving into the state and have the permit in hand BEFORE the move. Here is the section of the law relating to .50 caliber rifles:
4) A person moving into this state, otherwise in lawful possession of a .50 BMG rifle, shall do one of the following:
(A) Prior to bringing the .50 BMG rifle into this state, that person shall first obtain a permit from the Department of Justice in the same manner as specified in Article 3 (commencing with Section 12230) of Chapter 2.
(B) The person shall cause the .50 BMG rifle to be delivered to a licensed gun dealer, as defined in subdivision (c) of Section 12290 in this state in accordance with Chapter 44 (commencing with Section 921) of Title 18 of the United States Code and the regulations issued pursuant thereto. If the person obtains a permit from the Department of Justice in the same manner as specified in Article 3 (commencing with Section 12230) of Chapter 2, the dealer shall redeliver that .50 BMG rifle to the person. If the licensed gun dealer, as defined in subdivision (c) of Section 12290 is prohibited from delivering the .50 caliber BMG rifle to a person pursuant to this paragraph, the dealer shall dispose of the .50 BMG rifle as allowed by this chapter.
(c) A person who has registered an assault weapon or registered a .50 BMG rifle under this section may possess it only under any of the following conditions unless a permit allowing additional uses is first obtained under Section 12286:
(1) At that person's residence, place of business, or other property owned by that person, or on property owned by another with the owner's express permission.
(2) While on the premises of a target range of a public or private club or organization organized for the purpose of practicing shooting at targets.
(3) While on a target range that holds a regulatory or business license for the purpose of practicing shooting at that target range.
(4) While on the premises of a shooting club which is licensed pursuant to the Fish and Game Code.
(5) While attending any exhibition, display, or educational project which is about firearms and which is sponsored by, conducted under the auspices of, or approved by a law enforcement agency or a nationally or state recognized entity that fosters proficiency in, or promotes education about, firearms.
(6) While on publicly owned land if the possession and use of a firearm described in Section 12276,12276.1, or 12278, is specifically permitted by the managing agency of the land.
(7) While transporting the assault weapon or .50 BMG rifle between any of the places mentioned in this subdivision, or to any licensed gun dealer, as defined in subdivision (c) of Section 12290, for servicing or repair pursuant to subdivision (b) of Section 12290, if the assault weapon is transported as required by Section 12026.1.
This is the link to the DOJ site relating to Assault Weapons:
caag.state.ca.us/firearms/dwcl/12275.htm