Howdy Mas, first off-Thank You for all your shared information over the years. You have been a constant in my appreciation for pro opinions over the years. My question is about those 2 calibers: What's the biggest difference in these 2? I'll be possibly putting a conversion barrel into a G21 for the Super.40 and was wondering a little about it's history, as well as the 400 Corbon. Don't hear much about these. Thanks again.