The fixed mag can easialy be removed. Just pull out the trigger group then pull out the fixed mag, then reinsert the trigger group and viola, you are ready to use those types of removable mags. Just be wary, as I have read many complaints about various brands of mags jamming, that the only ones I buy are the 20 round Tapco mags. They haven't jammed on me yet and get great reviews form other shooters.
Changing from fixed to removable mags is so simple that I did it out at the range yesterday to burn through a couple of loaded mags, then I put the fixed one back in for the stripper clips. Only tool you need is a bullet to push the pin down.
