IIRC, what happened is the DOJ added certain SKS rifles to the list of AWs, and then gave owners 90 days to register them. Following the registration, they were sued by HCI I believe, who stated the 90 day extension was illegal. The DOJ lost and everyone who registered their SKS during that period was required to give it up. This didn't cause a huge stir because the SKS was not real popular. Had they tried that with the AR15, it would have been an interesting outcome (even they aren't that stupid).
This new bill seems to be modeled after RR89, but based on caliber, not model.
But it's still BS. They force you to register, which means you cannot pass it on to your kids when you die and at the same time do not allow you to own 50 BMG ammo.
So, you can keep it but you can't shoot it in California.
They can stick it up their collective arses.