Looking at the exploded diagram, 13 rounds might be a bit optimistic with the stock floorplate. It doesn't seem to have much more 'follower' size than my MKII, but I could very well be incorrect (I actually hope I am)GonzoP22-1 said:4. Mag looks VERY easy to mod to 13 to 15 rounds (just need to dremel out the little cutout on the side deeper. Strong type spring, too. A slightly extended floorplate (ala the Wilson mags on a 1911) and you can probably easily get to 16 rounds.