Para Mags
I recently had the same question about whether or not a 13 round mag would work in my Para Carry 12 (it's made for a 12 round mag). I went ahead and bought a Mec-Gar 13 round magazine and it fits just fine. There is, of course, an excess of magazine sticking out of the bottom of the grip. I made a plastic covering to fit around the excess part of the mag. I would say that the same would be true of your .40 caliber.
