I've never used an MGM barrel. One member on this forum had a Encore .460 MGM barrel and was having a devil of a time finding a load (handloading) that would group well - but that may not have been the fault of the barrel.
Instead of .44 mag, one option for you would be to use a factory 20" .460 barrel and load it with .454 Casul ammo. If I recall correctly, Indiana law on case length wouldn't allow the full .460 ammo but would allow .454 Casul. This would give you the added benefit of greater shooting distance (I'm thinking maybe even 50 yds more effective range).