Does anyone know if the 10mm mag can be used in either a 9mm or .38 super P220? Just curious if it would work without a bleep load of modification or 'just plain NO!'. Thanks!

I was able to check mine a few minutes ago. The magazines have the same dimensions overall.

Mine had the heel magazine release, but I have no reason to believe they would move the side mag release button.

FWIW, I was using the magazines that shipped with the earliest of 10mm P220s while cleaning a P220 from 1984 chambered in 9mm Steyr.

It should work fine.