All rifles in CA must have a minimum 16" barrel length, whether or not they are AWs, semiautos or bolt guns, etc.
Barrels shorter than 16" are short-barreled rifles (SBRs) and require special Federal permission/tax stamp - but more importantly are also essentially illegal in CA without special permission which you'll never get (just like machineguns, etc.) Bottom line, you can't have an SBR in CA.
IIRC, I believe there's a 26" min overall length for rifles too.
But in CA, any semiautomatic rifle with an overall length less than 30" is considered an assault weapon - regardless of features, regardless of presence/absence of detachable magazine.
As for pistol, don't try it. Even if you have a receiver that ATF allows to be considered a pistol since it was not built into a rifle yet ("once a rifle, always a rifle") it's illegal to build untested/unapproved 'unsafe handguns'. You can't make your own handguns in CA with the exception of certain single-action revolvers and, starting 2006, certain single-shot pistols - otherwise you've violated PC 12125.
Bill Wiese
San Jose CA