RE: rifle ballistics on 500 S&W?
Most of the guys on the NEF site that have chronograph ed them, claim they don't get much velocity increase with the 22 Inch Handi Rifle. I think they are pretty much loaded to their potential in the 10 inch revolvers.
A friend of mine has one in a custom built Encore and took a very large Alaskan Brown Bear with it. I believe he used the 375 Grain X bullet. One Shot.
In a rifle, I don't see it offering anything that you can't achieve with the 450 Marlin or hand loaded 45-70.