It is legal to get a G36 conversion in Ca, SL8's too. If there is not a bullet button or raddlock or any other device that requires a tool to remove the mag then it has cannot be shipped complete. The serialized receiver has to go FFL to FFL. Typically what happens is once you get the money the receiver portion is shipped to the FFL the upper in this case and all other items are shipped directly to the buyer. You might want to let them know they need to cough up some extra cash for shipping if done that way, you shouldn't get stuck with it. If you are shipping any mag over 10rds it has to be sent disassembled in rebuild kit form. Not sure if you have ever seen a website from Ca selling a mag that says "G36 10/30" for example. Basically that is a mag that was a 30rd mag but has been modified to only hold ten rounds. Sounds silly, but it is life for some. If it has the single stack magwell or double stack is really irellevant. Kind of funny in Ca you can buy a HK41 but not a HK91, just because the 91 is banned by name. If you have any other questions feel free to ask or PM me. I really should get with xfilterx and make a FAQ for this!