If I remember correctly, the 10 has a spacer. Use the spacer on thin walls. Don't use on thick walls. There documentation is usually pretty solid, I'd download their Quick Start Guide to determine what thickness doesn't need the spacer.
Anyone want to trade an MP10 + cash for an MP40w? I have a new 38g that I think might be too small for even a dialed-down mp40. Sorry to bomb the thread..........