R50 stands for Rifle 50 Rounds, in complementing contrast to the P50, the pistol version of the same platform.  The CA version, however, ships with a 10 round magazine. 

Federal law requires firearms to be shipped to FFL Dealers. If you do not specify the name and shipping address of your dealer, your order will be delayed. Federal law requires that you be 21 years of age or older to purchase a handgun, frame or receiver. To purchase a shotgun or rifle, you must be 18 years of age or older. 18 U.S.C. Section 922(b)(1).

Note about our photos:
While we make every effort to ensure that our product photos are accurate, manufacturers occasionally change the design of components such as triggers, sights, or magazines without notice. Also, modifications to the firearm or component may be required in order to meet specific state compliance requirements. While we make every effort to accurately describe and illustrate the item you are going to receive, there may be visual differences on various components that do not affect functionality.

WARNING  Cancer and Reproductive Harm  www.P65Warnings.ca.gov