Gary, Nothing is done to the mag well or the rifle to limit size of magazine you can use. The magazine will take as large of magazine as they make for it.

Gary, Paul is not totally correct. If you bought your standard or large capacity magazines during the freedom week period and had the receipt no problem with those magazines.

You could physically put a 100 round drum mag in an a rifle thats CA compliant and it would still function, if you were caught doing so you could face potential felony charges that could lose you the right to own any firearms moving forward, and I believe that California specifically you can be charged criminally for just possessing a magazine that holds more then 10 rounds ( you don't have to be using it in a rifle or handgun just having it on your person is considered illegal contraband)