I found a California compliant Sig 516 online and I believe the only additional feature California requires that NJ doesn't is a "bullet Button" to release the magazine. 

 

If I buy this gun -- Can it easily be converted back to standard magazine release?

 

Other then coming with a 10 round mag is there anything else I should know about a California complaint gun?

 

Thanks, Rich 

The answer is: it depends.  Some OEMs stake the maglock and it's much harder to remove.  I don't know if Sig is one of those since it seems they don't ship CA-compliant rifles from their factory.  I say this because I have tons of 516 and 716 rifles come through my hands for CA dealers who buy them from Sig and have them shipped to me to have the maglocks installed prior to shipping them on to them in CA.

You could always call Sig directly and ask the question > 603-772-2302

Thanks for the response. I'm not going to be ordering a CA gun, after some additional reading the stock is adjustable and it's equipped with a flash suppressor. I didn't realize that was legal in CA. 

Stock can be disabled and an muzzle brake can be pinned and welded on like most AR rifles