Max capacity, irregardless of what the gun will hold, is 10 in the magazine and 1 in the chamber. I load my first magazine with 11 the rest with 10. That way you don't have to mess with a "BARNEY MAG". Be sure and clear that with your Range Officer or Match Director first.
I'm pretty sure you can use any high capacity mags as long as they are loaded to 10 rounds.
I am the Christian Conservative that CNN warned you about!!