Say I had an AR-15 that was converted to .22LR with a Ciener kit, and I had to move to Kalifornia, would it be legal or not? SB 23 mentions *centerfire* rifles as evil, not rimfire. This is probably a much beaten question, but I am very curious...

I'd like to know the answer to that myself, and I live here. Several ideas have been tossed around...

I think the .22 mod would have to be permanently installed. With a dedicated .22LR upper that could be as easy as tack welding the front takedown pin so the upper can't be removed, but you could still open it up for cleaning by pushing out the rear takedown pin. A .223 barrel with a Ciener kit might be a gray area because technically you could still use centerfire ammo with it.

Another option would be to permanently fix the .22LR mag in place (ala FAB10) to get rid of that evil feature.

IIRC, someone wrote CA DOJ and asked these questions, but DOJ's answer was vague. They basically said to read the law or ask local law enforcement, which is pretty much their pat answer to any clarification questions. You might write DOJ and see if they give you a better answer.

DOJ would want to examine the upper and lower before making a determination.  The upper is not the problem as it is just a component, it's the lower you would have the problem with as it's a .223 lower, was made as such and will always be one.  

Finish an 80% lower and you can stamp it .22LR or anything you like.