Check out this video from FN USA from January 2012 (try to ignore the speaker, he sucks):
The magazine is one of the "new" T8.1 magazines- look closely when the speaker removes the magazine, you can see the slots going all the way through.
EDIT: It also has a magazine bumper (to protect the mag if you should eject and drop it).
Interestingly enough, the FN303P's product page says the mags only hold six shots (maybe because the rounds are heavier, they need a stiffer spring?) and, it says the gun has a "stainless steel firing engine".