I don't know all the details, but as I understand it, California has a whitelist of firearms that are allowed to be purchased. If the firearms is not on the list, it is not legal to purchase. It goes by model number, so a manufacturer makes the slightest change to a firearm and create a new model number for it, then the new model number has to go through the whole process of being re-submitted to be approved. Which I also understand requires providing samples and going through testing the manufacturer has to pay for, its lengthy and beuracratic. On top of that, like good little anti-gunners, they will play games and find some excuse not to approve a new firearm despite their be absolutely no reason not to approve it.
The whole premise of this was gun safety, as they refuse to approve new models with improved safety and force owner to purchase older used models with less safety.
To the OP, doesn't California have a website to check the handgun roster? Can't you simply look up the make/model and see if its legal to purchase or not? Or is California so bad, they play "I have a secret" with the firearms they allow you to purchase.