IIRC the law says it has to fit in a box 130x180mm, the P17M13 is 175x135mm, so it ought to be too high to be a "muu ase", right? I've tried to verify it and so far it seems to hold up, the HK P17M13 should not fit in the magic box, I would like some verification to know for sure though.
Kiitos paljon!
EDIT: as you can see with this photoshop, the box is not big enough to contain it, too high, doesn't matter how you swing the box, it's a very close call though.

I understand there is also another box of 140x190mm but that should be for revolvers only?