I live in Calif, and am up on current Calif law. Technically and I say technically it is legal to ship high capacity magazine parts into Calif.
The reason behind the law allowing import of mag parts into Calif. is If one of your legally owned mag breaks you can buy parts to fix it.
The problem I see is when a party inside Calif asks you to send ALL the parts of a mag to him. I would not do that just because I would imagine the fellow may just put the parts together.
If it was just a follower, base plate or spring I would not hesitate to send the part.
A complete mag dissembled although TECHNICALLY legal I would NOT send here. Just not worth the risk.
Here is the code pertinent to "large capacity" ( over 10 rounds) magazines in Calif:
Penal Code 12020 (a)
Prohibited activity
(2) Commencing January 1, 2000, manufactures or causes to be
manufactured, imports into the state, keeps for sale, or offers or
exposes for sale, or who gives, or lends, any large-capacity
magazine. (felony)
Allowed usages
19) The sale of, giving of, lending of, importation into this
state of, or purchase of, any large-capacity magazine to or by any
federal, state, county, city and county, or city agency that is
charged with the enforcement of any law, for use by agency employees
in the discharge of their official duties whether on or off duty, and
where the use is authorized by the agency and is within the course
and scope of their duties.
(20) The sale to, lending to, transfer to, purchase by, receipt
of, or importation into this state of, a large-capacity magazine by a
sworn peace officer as defined in Chapter 4.5 (commencing with
Section 830) of Title 3 of Part 2 who is authorized to carry a
firearm in the course and scope of his or her duties.
(21) The sale or purchase of any large-capacity magazine to or by
a person licensed pursuant to Section 12071.
(22) The loan of a lawfully possessed large-capacity magazine
between two individuals if all of the following conditions are met:
(A) The person being loaned the large-capacity magazine is not
prohibited by Section 12021, 12021.1, or 12101 of this code or
Section 8100 or 8103 of the Welfare and Institutions Code from
possessing firearms or ammunition.
(B) The loan of the large-capacity magazine occurs at a place or
location where the possession of the large-capacity magazine is not
otherwise prohibited and the person who lends the large-capacity
magazine remains in the accessible vicinity of the person to whom the
large-capacity magazine is loaned.
(23) The importation of a large-capacity magazine by a person who
lawfully possessed the large-capacity magazine in the state prior to
January 1, 2000, lawfully took it out of the state, and is returning
to the state with the large-capacity magazine previously lawfully
possessed in the state.
(24) The lending or giving of any large-capacity magazine to a
person licensed pursuant to Section 12071, or to a gunsmith, for the
purposes of maintenance, repair, or modification of that
large-capacity magazine.
(25) The return to its owner of any large-capacity magazine by a
person specified in paragraph (24).
(26) The importation into this state of, or sale of, any
large-capacity magazine by a person who has been issued a permit to
engage in those activities pursuant to Section 12079, when those
activities are in accordance with the terms and conditions of that
permit.
(27) The sale of, giving of, lending of, importation into this
state of, or purchase of, any large-capacity magazine, to or by
entities that operate armored vehicle businesses pursuant to the laws
of this state.
(28) The lending of large-capacity magazines by the entities
specified in paragraph (27) to their authorized employees, while in
the course and scope of their employment for purposes that pertain to
the entity's armored vehicle business.
(29) The return of those large-capacity magazines to those
entities specified in paragraph (27) by those employees specified in
paragraph (28).
(30) (A) The manufacture of a large-capacity magazine for any
federal, state, county, city and county, or city agency that is
charged with the enforcement of any law, for use by agency employees
in the discharge of their official duties whether on or off duty, and
where the use is authorized by the agency and is within the course
and scope of their duties.
(B) The manufacture of a large-capacity magazine for use by a
sworn peace officer as defined in Chapter 4.5 (commencing with
Section 830) of Title 3 of Part 2 who is authorized to carry a
firearm in the course and scope of his or her duties.
(C) The manufacture of a large-capacity magazine for export or for
sale to government agencies or the military pursuant to applicable
federal regulations.
(31) The loan of a large-capacity magazine for use solely as a
prop for a motion picture, television, or video production.
(32) The purchase of a large-capacity magazine by the holder of a
special weapons permit issued pursuant to Section 12095, 12230,
12250, 12286, or 12305, for any of the following purposes:
(A) For use solely as a prop for a motion picture, television, or
video production.
(B) For export pursuant to federal regulations.
(C) For resale to law enforcement agencies, government agencies,
or the military, pursuant to applicable federal regulations.