AR-15 22 Conversion Legal?

Am new to the AR world and have a question. Are the various 22LR conversion uppers (not the Ciener type bolt replacements...)legal in Calif? I have read that various interpretations of the (old) AWB allow 22LR uppers mated to pre-ban lowers and since it is a rim-fire weapon it was exempt from the AWB anyway.... Can anyone explain please?[?]