The 15 and the 17 round are standard for the full size there is also a 20 I believe that extends a little below the standard VP9 or P30 grip. The SK will run the longer mags but there is no plastic adapter that I am aware of. I don’t know if HK or someone makes a spacer - they might, no doubt it would be extra. Nice pistol I like the optic ready version but the optic plate is extra.