Full story at http://www.crpa.org/_e/page/1597/mr01_18_2011.htm but short version is that the ban on mail order sales and all sorts of goofy storage and record keeping requirements were struck down as unconstitutional on account of “vagueness.”
The sticking point being that it is impossible to figure out what “handgun ammunition” means, so the law has been thrown out before it was supposed to go into effect on 1 February, 2011.
That is the good news.
The bad news is that it is very easy to fix by changing “handgun ammunition” to “all ammunition” and the vagueness problem is fixed and people are worse off than before.
Given the chronic tendency of the California Legislature to do stupid things, that “fix” is their very likely solution to a non-problem that would be best addressed by repealing the first version.