the 10 round limit is on a Tubular magazine if you ordered this one with the Box mag it should be legal budsgunshop.com/product_info.php/products_id/100883 I would check with the local ffl where you were having it shipped to be sure budsgunshop.com/feeds/state_reg/california_restrictions.pdf

Matthew, you are fine Sir. i have checked all of Buds 590's and the magazine is a 10rd magazine and would be an 11rd shotgun with one round in the chamber. California only counts the magazine capacity and not the plus one in the chamber. If this were not true, you could not buy a 10rd magazine handgun that can hold 11rds with one round in the chamber. Cheers and you and yours stay safe!