All I THINK I know is that if you handload, you should only load bullets designed for .454 type pressure as the softer ones can actually increase pressures and not shoot well. Or so I've read.
A guy I met at he range had the .460, .500, and .50 ML barrels in 20". He loves 'em. I didn't get to shoot his but I did heft it and it was very handy.